Johnson Valiant Modifications

JOHNSON VALIANT MODIFICATIONS

THE RF STAGE AND POWER SUPPLY REGULATION

Low level and driver stages, clipper and filter; inverse feedback

UPDATE 1/14/2017: "Johnson Viking Valiant Mods by WA1HLR & Using correct P-T156 or 124B Hammond transformer".

This web page is a blog about the process I used to make the E. F. Johnson Valiant into the transmitter I wanted it to be. I make no apologies whatsoever for its rambling nature. You may learn something from the engineering analysis and thought process, if you take the time to read it. This most certainly is NOT a one page, modification sheet. A radio of this complexity cannot be analyzed in one page. In ALL cases I have attempted to give credit to the sources I used to improve my Valiant. These authors include W8JI and WA1HLR. If I failed to note you as a source, please send me an email and I will credit you. I provide a link to the source material, so that you can decide if you want to use those ideas in your work. I got a LOT of questions on Timtron's work. I have photos and a schematic showing exactly how to do those mods. I do not rip off someone else's work. Accordingly, I have moved the part of my article employing the WA1HLR modifications (posted on amfone) to its own page: JohnsonValiant5.html.

There is a lot of confusion resulting from the choice of whether to keep the original Valiant audio configuration (single ended driver stage) with minor mods (W8JI and WA1HLR) or using the extensive mods PUSH PULL DRIVER STAGE contained on my site. I get a lot of inquiries about the WA1HLR Valiant mods; Tim provides a good written description of how to improve your Valiant. I used his mods and added my own. I provide in the link above, photos and schematics which include his mods, to clarify some ambiguities in the written information. I recommend you do ALL of the Johnson Valiant Modifications by WA1HLR FIRST; THEN replace the Johnson Valiant Driver Transformer with the P-T156 or P-T156 or the Hammond 124B. This will take you a LONG way. My full replacement with a push pull audio driver circuit is a huge job, and will make smaller but significant improvements, should you care to go to all the extra work, as a "level 2 modification".

WA1HLR says: "The anemic modulator has all it can do to reach 100% modulation. The audio quality is that of two dixie cups and a string." This is substantially the fault of the stock Johnson Valiant Audio Driver Transformer.

About the stock Johnson Valiant Driver Transformer, Chuck Felton, a well known professional restorer of classic equipment, states: "It is the worst thing you could have after a clipper; it's trash." You gotta love a man who calls it the way it is.

ADDITIONAL NOTE: If you want to do any of the mods like the W8JI or the TimTron mods and keep the single-ended stock 12AU7 paralleled configuration, consider the P-T156 or Hammond 124B. The 124A is more like the original Valiant or other Johnson rig driver interstage, but for the small increase in price, buy the 124B and get better than original performance. The P-T156 works well, and only costs $16.

If your Ranger, Viking II, Valiant, or other Johnson Transmitter burns out an audio interstage transformer, this is the replacement that works perfect and fits the original bolt hole pattern. It also would be perfect for a DX100 or Heathkit Apache.

This is a true high fidelity transformer. Read the specs at: http://www.hammondmfg.com/124.htm.

This section continues the discussion of the Valiant modifications that I have been working on for the last year. This discussion refers to the schematics on this page showing the mods. I make no attempt to be concise here, and ramble a lot about design details. Refer to the original EFJ schematics and my drawings and photos as you read this article. Skip the article and look at the schematics.

This modification does not show on the front or above the chassis and operates all components within manufacturer specs. It tunes up the way the stock rig should as described in the original EFJ manual. A trapezoid display of the modulation pattern is textbook perfect for linearity when done. Largest cost item is the driver transformer, which is about $25. Another mod transformer and 811s and other blasting and drilling might provide marginally better performance, but why not get a clean chassis and equipment rack and just start over your way instead of modifying this rig?

I make reference to other people's work in this article. I researched what others were doing as I was developing my plan of action, just as you are looking my ideas over. Nothing here is meant to denigrate their designs. I looked at their choices, and made different choices for myself. I offer the reasoning for why I departed from those prior articles. It is not throwing rocks at someone else's work. Everyone has their own solution; just because they differ does not mean that one or more of the approaches is wrong. I present my reasoning here, and the alternatives to my approach; you are free to explore options. I hope you will find something useful.

The parentage of my final version Valiant is as follows: nothing of the "East Coast" mods survives. The RF stage, modulator output stage, and VR tube modifications closely parallel the work of WA1HLR as posted on line. We all owe Tim a lot both for the information he shares freely with others as well as the preservation of the art and science of classic AM radio. The fixes for flaws like the drive pot also come from him. From the grids of the 6146 modulators to the line or mike input, I wanted a better driver transformer, so all the rest of the design work is mine.

The three 6146s in the RF stage are to be standard 6146s, not 6146B. These are reserved for the modulator, as detailed in the first article explaining why the Valiant strains to obtain sufficient audio power to fully modulate the RF stage. How Johnson missed the correct biasing of the RF finals is beyond me. Running three 6146Bs in the RF deck does not provide a worthwhile increase in power and it DOES increase the DC flowing in the modulation transformer for only 20% more, not a good idea. You CAN run 6146Bs in the final at standard 6146 ratings. The neutralization and bias will work just fine, if you follow the correct procedures in EFJ manual. You WILL benefit from higher plate dissipation safety factor with the B version. Getting full power from paralleled finals depends on good matching of the tubes, and this gives you some wiggle room. As I note elsewhere, not all radios tolerate this substitution well, especially compact SSB radios. The 6146A has more emission and tolerates low filament voltage better than the standard 6146, but has the same plate dissipation specs.

The design shown here has about 8.2 mA per tube screen current at +180 V. This is less than the EFJ design and is closer to the tube designer's figures shown below. You may want to increase the screen resistor more. This shows good trapezoid pattern and does not over stress the 6AQ5 clamper. The grid bias is obtained more from grid leak than the original EFJ design, which makes better linearity in the RF stage under modulation. It is critical to note that the Valiant One calls for 50 mA resting current on the RF finals in SSB mode. The Valiant 2 calls for 100 mA. WA1HLR recommends 100 mA per a conversation we had on the air. Use 100 mA as it is a lower fixed bias voltage, allowing the grid leak resistor to do its job properly.

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If you have not done it yet, update the bias pots to the newer configuration, not the old style slider power resistor style in the Valiant One. You can drill small holes in the outer case to allow bias adjustment to compensate for tube aging without removing the cover as shown above. Use the online resources to compare the two configurations. I may include a drawing on this page also. Updating it is not difficult at all. I adjust Resting Modulator current to 55 to 60 mA. I found the 80 mA figure does not measurably help with linearity and only causes unnecessary heat and stress on the 6146Bs. Others differ and say to run them hot. I try to keep things as cool as possible so that if the current drifts up, I do not have to take immediate action to prevent China Syndrome.

Intermittent Commercial and Amateur Service (ICAS ratings) PER TUBE. Multiply by 3 to get the Valiant Numbers.

STANDARD 6146 OR 6146A SPECIFICATIONS (Class C Plate Modulated Telephony)

GE TRANSMITTING TUBE MANUAL, 1955 Radio Amateur's Handbook, RCA TT-5

Plate Voltage: 600

Screen Voltage: 150 (Maximum screen power 2 or 3 W depending on who you ask).

Grid Voltage: -87 (Some hams like -100 to -120V)

Plate Current: 112.5 mA

Screen Current: 7.8 mA to 12 mA

Grid Current: 3.4 mA EFJ says 3.0 mA, which I use. ( CCS says do not exceed 3.5 max in RCA TT-5 manual. ICAS says DO NOT EVER EXCEED 4 MA!)

I PERSONALLY RECOMMEND OPERATING GRID CURRENT AT WELL BELOW ICAS AT 3 MA PER TUBE OR 9 MA ON THE VALIANT FOR LONG TUBE LIFE.

Plate input power: 67.5 W Max

Power Output: 52 W approx.

Efficiency: 77%

Timtron attributes premature tube failure to excessive SCREEN grid current and wattage. The EFJ design seems to push the limit on this.

W8JI makes no observation on this point. He does not specify the resting current setting and uses a 10K grid leak resistor.

The tube handbook maximum grid leak resistor is 27K for class C stages.

My experience has been that a higher value of grid leak resistor is less tolerant of 6146s that exhibit negative grid current in standby.

I found Tim's approach to achieve the best balance between good linearity and tube life, and follow it generally here.

Excessive grid drive or plate dissipation from off resonance operation and the like eventually results in the grid meter deflecting below zero when in the CW mode and unkeyed with the plate voltage applied. Once this occurs, the 6146 has been irreparably damaged.

You might be able to get some more use from it in an application that has very low grid circuit resistance, such as the modulator. I have not verified if they are OK in this case. The abuse of tubes does not result in either worthwhile S meter readings or marginal audio improvements on receive.

Adjust RF plate resting current to 100 mA in SSB. Adjust clamper per EFJ manual.

Tune up in CW for:

3 X 3 = 8.5 to 9 mA grid MAXIMUM. NEVER EXCEED 12 MA!!!!

3 X 110 mA = 330 mA plate

Plate voltage about 630 V in Valiant. Remember the screen current is included in the displayed plate current as measured in the Valiant since it is Cathode current.

This is conservative and allows a little wiggle room for mismatched 6146s in the RF stage.

Approximate RF output power is measured at 150 W as EFJ specifies. I experienced no loss of power from raising the screen resistor value.

Modulator resting current set to 55 to 60 mA. Peak modulation may peg the meter now due to increased power. Average may run 165 mA. But use a scope. Your neighbors on the band will appreciate it.

MODULATOR OUTPUT STAGE CONSIDERATIONS

VERY VERY IMPORTANT!!! DO NOT TEST THE MODULATOR FOR EXTENDED PERIODS AT FULL OUTPUT! Use a signal that keeps the modulator plate meter below 100 to 125 mA. The tubes and other components are not designed for continuous sine wave output at maximum levels. The modulator will operate perfectly safely with normal speech waveforms, even with heavy compression or clipping. You can run frequency response curves at lower levels and still get good data. If you run high level tests, such as 100% modulation tests with a trapezoid pattern, limit them to a few seconds maximum, and allow adequate time for cooling. If at any time, any of the plates of the 6146s show any color, STOP IMMEDIATELY.

The example you may be familiar with is that of, say, an Ameritron AL811. You may safely operate it at 500 watts on intermittent waveforms. You must reduce drive till the output falls off if you intend to use it in RTTY or full carrier AM. This precaution is of the same nature, to observe the AVERAGE power restrictions.

NEVER operate the modulator power stage without the RF power amplifier operating and properly tuned. The RF stage is a resistive load to the modulator and without it, the modulation transformer will be instantly destroyed. Most people are used to integrated AM rigs with all the necessary circuitry supplied. In the instance of an Eico 720 transmitter and 730 modulator, two separate units, the mod transformer sometimes is destroyed by people unaware of this precaution.

I include these warnings to those who might be new to the AM technology to apprise them of the fundamentals, so that they may avoid hard lessons.

I added negative cycle loading. The modulator originally did not develop enough power to endanger the modulation transformer by forcing the level to exceed 0% negative peaks. Now the transformer may drive the final to less than zero volts on the plate, causing it to shut down (its a diode for this purpose). Without the approximate 2K load of the RF final, voltages soar and the modulator transformer or components may arc. The rig I have originally DID arc to the point that it required an extra set of standoffs to attach the transformer leads with sufficient insulation. The negative cycle loading consists of sufficient 1N4007 diodes (for Peak Inverse Voltage Rating) and a 2K resistor which is switched in by them to continue loading the transformer. See the arcs and sparks discussion I posted.

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I had a whole discussion of high level splatter filtering that I removed from this article. It may be a separate article in the future. There are lots of risks to the components of the Valiant by messing around with this technique. There is a technique to testing frequency response of mod transformers or splatter filters at low levels with resistive loads to simulate the tubes. I got what I wanted without using a high level splatter filter.

The low level clipper can be built out of more common parts. If you mess up the design, it probably won't destroy anything. It still limits splatter, a good thing. You do not constantly have to ride the gain and stare at the scope to keep your audio from hitting the baseline. The mistake people make employing the clipper is to run it at 25 dB clipping to obtain more punch. What they get is fuzzy distorted hard to understand audio. Using 3 to 6 dB will not be noticed. Properly adjusted, the clipper prevents splatter. The LC filter in a pi network configuration blocks harmonics generated during clipping and undesired high frequencies from passing to the power stage. This prevents excessive bandwidth. Even the external audio chain in my design enters before the LC filter. In the microphone input amplifier, a small capacitor across the level control and a small capacitor across the phase inverter aid in the suppression of excessive bandwidth. Additional shunt capacitance is across the modulation transformer to limit excessive bandwidth, as discussed in this article. It is shown on the schematics.

If you wish to omit the clipper or even the filter, I have provided points on the drawing where the deletion of the undesired components and the use of an appropriate coupling capacitor will get you to the version YOU want. What you will wind up with is a transmitter that has the RF final biased correctly, and a real class AB2 modulator with a low distortion driver that will do about 50 Hz to 8 KHz if you remove the band limiting components. I leave it to you to customize the final product to your preference. You might be able to eliminate the extra 6AV6 also. I will leave that up to you. To connect the mike preamp stages (12AX7) to the driver stage directly, attach point "X" to point "A" or "B" with a capacitor and resistor of appropriate value and rating. If you remove the clipper, you can use the front panel clipping control for a level control for the outboard audio from the line input, if you wish. The capacitor should be selected for appropriate low frequency response. The series resistor should be selected to avoid over driving the following stages. I have provided approximate AC and DC voltages on the schematic for guidance. These levels were obtained with the front panel controls set for nominal correct operation: about 9 o'clock for audio and full clockwise for the clipping to avoid interaction during testing. In operation, it will be about 10 o'clock with the resistor values shown. Use a scope to set it properly.

I mounted the upper frequency limiting capacitors near J8 on an existing terminal strip. That way it is easy to swap values as you do performance tests. You might want to put them inside the J8 mating plug, so that you can switch them around for varying operating conditions. This capacitor "builds out" the modulation transformer as is commonly done in those days. NOTE: high voltage is present on J8; use good construction techniques and for safety sake, be sure that the metal cap on the plug is insulated from all wiring and components. I may post something that shows how to do select capacitors to "build out" the mod transformer without having high voltage on the transformer. But it is in the 1950s handbooks, if you wish to research that.

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The terminal strip that wires to the mod transformer are shown below for your use. This information is not directly in the Valiant manual; it takes a while to dig it out and verify it. You will need it if you are testing the transformer with power off. Unplug the tubes and use the 6146 plate caps with a signal generator and a simulated plate impedance resistor(s), driving it push pull with a center tap to chassis ground to keep things modeled properly. Unplug J8 and monitor the output with a proper low power resistive load (about 2K or 630 volts divided by 330 mA) to simulate the RF stage. Adjust the capacitor values and sweep the frequency to observe the effect of the test values on the terminal strip nearest J8. Be sure to account for the capacitors in the other side of J8 and in the RF stage near the big plate RF choke in the final compartment. There is no risk to the components or safety hazard by doing this "power off" testing. Once you have settled on a value that does not generate unwanted resonance peaks that might damage things, solder the test capacitor on the terminal strip and reassemble things and do a "power on" test to verify your work. Use a scope as well as a receiver with a narrow filter to check your splatter while transmitting into a dummy load. The original EFJ values are totally safe. I opened it up very slightly but did not exceed 3500 cycles. I do not recommend values that are smaller than those on my schematics or in Tim's article.

The first entry is the terminal nearest the front panel. The last entry is the terminal nearest the back panel.

Yellow to RF plates

Red-Yellow and Green sort of center tap of transformer to J8 (to use Valiant to drive an external modulator grids)

Green-Yellow to HV B+ via J8

Red to Modulator HV B+

Brown to Modulator Plate

Blue to other Modulator Plate

The 6146B modulator screens need a series resistor of about 270 ohms and changes to the regulator tubes to reduce audio energy present at the screen. There is a 10 to 20 uF capacitor to stabilize the screen voltage and a 330 ohm resistor to prevent the VR tubes from motorboating in and out of ignition (called relaxation oscillation). I adopted this fix and found it reduced distortion at drive levels in excess of 70% modulation just as he said. See the schematics for the wiring details. See the photos for the mechanical details. This is a key modification that is absolutely essential to the proper operation of the whole system described in this article.

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PROBLEMS WITH ARCS AND SPARKS

This problem is why I did not do the extra mods in the "East Coast" version to increase the modulator B+ to 1000V. Perhaps if I had done those mods and they worked without flashing over, I would never have gone this route. As is stated in WA1HLR's article, you have to do the whole set of modifications in any article to get the performance increase expected; half way just does not cut it. I failed to do that in the case of the “East Coast” mods and did not get 100% modulation without distortion. Maybe you can get a HiPot tester on loan from a friendly electrician to determine if your rig will tolerate the higher B+. Of the five Valiants that have crossed my workbench, none of them appeared up to the task.

Here is why the high voltage power supply has problems with the 866 filament wiring and high voltage choke wiring.

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Even the terminal strip for the modulator windings can arc. This shows an added standoff to correct that situation.

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Take a look at the separate article with pictures of the previous damage inside an unmodified Valiant, and you will understand why I did not proceed with mods posted on the net. People have done the “East Coast” mods successfully with the high B+ mod implemented and experienced no problems, so decide for yourself what you want to do with your radio. Inspect carefully for any arc points in the radio before doing any mods. I include pics of arcing on the terminal strip for the filaments of the 866. Also, the wiring for the HV plate filter choke are insulated with additional sleeving. There is another terminal strip near the LV fuse for the 866 filaments which can cause trouble. Sleeving may be required on the 2.5 VAC filament wires into the LV transformer. The 4 pin sockets may arc. (The Viking 2 is notorious for this, and all that is required is to put insulating spacers and ¼ inch longer mounting screws on the sockets for the 5R4s.) Replace the 866s with 3B28 tubes to avoid mercury warmup issues with resulting flashover upon application of HV power. I have commercial solid state replacements in my rig. The modulator transformer terminal strip is a possible problem. Ceramic standoffs help. The back panel jumper connector J8 is a possible problem. All these potential problems are the reason I did not attempt the “East Coast” mods that raise the HV B+ to 1000 V on the modulator.

Some people have had success with this approach, but looking at the wiring harness and all these known failure points, I sought another solution. This one worked out OK for me. Look it over, and see if it will work for you. A new $25 driver transformer goes a long way toward improved performance. This one makes full modulation and decent frequency response without exceeding ICAS tube ratings or risking failure of old wiring due to “hot rodding” the HV power supply.

INSTRUMENTATION IDEAS

I added a sample point for the modulated B+ to feed the horizontal deflection of my monitor scope. This allows the RF to be on the vertical deflection for a trapezoid pattern as shown in some of the 50s handbooks. At the completion of these modifications, I got a perfect textbook pattern. It is a lot easier to judge a straight line on the side of a triangle than guessing at a peak of a speech pattern for linearity. You can strive for linearity in the audio system and fail to get the RF biasing correct and wind up with distortion that is hard for a receiving station to characterize. Circuit constants shown are good to below 100 Hz for the sample circuit. The modulated high voltage sample comes out to an RCA jack just below the SSB jack. Its hard to find a spot to mount anything on the back apron without ruining a harness. All my instrumentation is located here. Before you add a trapezoid test point, be sure to read all the article here about it and observe proper electrical safety procedures to avoid equipment damage and shock hazard. If you do not have training or experience with tubes and high voltage, do not attempt any of the modifications described here.

I disconnected the SSB drive input wire from S4 and the 100 ohm resistors and placed the loose wire end near the grid tank coils. Insulate the end and anchor it with tie wraps so it does not short into anything. I connect an external frequency counter to the back panel jack to spot on frequency with this signal without actually putting a signal on the air.

You will see in the photos that I have not retained the original meter shunts. I began my career in a calibration lab. So I check and often remove or trim the values of the original shunts if they are not accurate to 5%. The wire shunts EFJ uses do not lend themselves to calibration well, and are nearly impossible to solder to. Copious amounts of flux and heat are required. Generally they are way off calibration. My rig on RF plate was over 20% off. The Grid meter reading was also way off calibration. Due to the common availability of accurate low value resistors these days, I have no reservation about hacking these out and ditching them for better calibration. It is very difficult to directly measure the low ohm resistors. The end result of accurate current readings is easy to achieve without specialized four lead ohm meters. I was unable to convince a friend to do it this way after lengthy discussion. I suspect he got inferior results and wasted much time the other way. A small variable supply or 12 volt supply and variable resistor are all that is needed to get the panel meter to 1% if you wish using a modern digital meter. These tests are done with the Valiant unplugged from the AC power. Simulate the current in the circuit with a power supply with a digital milliameter and current limiting resistor in the lead and observe the panel meter. The Valiant should be in the normal horizontal position to avoid gravity effects on the Valiant panel meter. This is really important to do before you attempt any modifications. Think about it. If your plate meter reads high, and your output power is low, are you really running rated input power? Bad data does not help you tune up your rig properly.

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If the panel meter reads lower than the digital meter used to calibrate it, a resistor must be inserted in series with the multiplier resistor in the Valiant. This is pretty straightforward. Increase the value of the Valiant resistor by 1% if it reads 1% low.

If the meter reads higher than the digital calibration meter, a shunt resistor is required across the existing resistor to reduce its value.

Here are some helpful rule of thumb approximations if the meter reads high:

If the meter reads 20% high, put a shunt resistor across the multiplier resistor 5 times the value of the multiplier resistor and the panel meter.

If the meter reads 10% high, put a shunt resistor across the multiplier resistor 10 times the value of the multiplier resistor and the panel meter.

If the meter reads 5% high, put a shunt resistor across the multiplier resistor 20 times the value of the multiplier resistor and the panel meter.

If the meter reads 2% high, put a shunt resistor across the multiplier resistor 50 times the value of the multiplier resistor and the panel meter.

If the meter reads 1% high, put a shunt resistor across the multiplier resistor 100 times the value of the multiplier resistor and the panel meter.

This process can be done repetitively to approach the value with higher and higher shunt calibration resistors until you get as close as you wish.

If you need to fix the RF plate or Modulator multiplier resistors, the best way is to hack out the original resistance wire loop and replace them with a real precision resistor which is cheap and commonly available. Get one slightly higher than the 0.404 or 0.202 ohm values specified by EFJ for the RF and Modulator Plate Current shunts and trim them down by the methods shown above.

This process is explained in detail, along with the proper mathematics in the separate article on this page regarding meter calibration.

THE DRIVER TRANSFORMER

The key element to this whole modification is this sweet little driver transformer, the 20A14, that is still available off the shelf. Most modifications try to cope with the limitations of the original driver transformer. I do not. Turns ratio is one to three step up, full primary to full secondary. A Thordarson design, it does not exhibit the nasty 100 KHz region peaks and resulting phase shifts the stock EFJ transformer has. These high frequency peaks complicate stability in an inverse feedback loop. In early hi-fi designs, knowledgeable engineers soon distinguished themselves in the community by doing their homework on the transformer design. No amount of inverse feedback can fully correct the flaws of a crappy transformer. The 20A14 bolts up to the same holes the original EFJ transformer uses! An insulator may be required on the frame to keep it from shorting out the terminal strips below it on the chassis. You will have to excuse me while I rave about the beautiful specs of this transformer. The primary is better than 20 Henries. The secondary is an astonishing more than 200 Henries! (The stock EFJ driver transformer is only 1 Henry on the primary and just under 10 Henries on the secondary.) Wow!!!!! No wonder the low end response of the 20A14 is so fantastic! When you get done with your modifications, run a 500 Hz square wave from the line input and you will see what I mean.

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OK sorry, I wore the markings off the exclamation point on my keyboard. I did compare (and reject) an alternative 20D89 transformer, also available off the shelf. It measured 1 Henry on the primary and about 11 Henries on the secondary. I considered it briefly because it is push pull plates to push pull grids. It fell far short of the 20A14. The iron is almost exactly the size of the EFJ stock transformer, so the inductances are about the same. There is little cost difference between the 20A14 and the inferior 20D89. Notice how much bigger the 20A14 is. It is sort of like being too rich or too thin. You never can move enough air through an RF amp or have too much iron in your transformer.

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Also, the secondary of the 20A14 is two separate windings. You might be curious about this. Old Buzzardly designs in the 1950s handbooks allowed a complex inverse feedback loop inside the power stage by feeding energy from one tube plate to the opposite tube grid with a resistor from the transformer return side to ground or bias. This configuration resembles the neutralization of an old school plug in coil push pull triode RF amplifier. This would be a dynamite way to reduce the distortion generated in the modulator power stage, except for one thing. Due to the resistance in the grid return, and the need for grid current for class AB2, it won't work right. Bummer. However, if you cannot find any more 2A3's to drive your 811s, you CAN use this scheme with a pair of pentode connected class AB1 6L6s and this 20A14 transformer and get the low output impedance drive for the 811s! More to come........

Some people recommend using the 20A14 driver replacement transformer I have as a step DOWN. This looks good on the surface to obtain a lower drive impedance for the modulator grids for AB2. If you look at the load line drawing on the tube characteristic curves I made, it shows that the 12BH7 is out of limit on plate dissipation and nonlinear. Hooked up as a step UP, it works correctly. I used feedback around the audio system from the output of the driver to grids and sent it back earlier in the audio chain just after the Low Pass Filter. This results in the desired low impedance in the driver, which is essential to achieving class AB2 which draws grid current in the 6146B. Again, a magic incantation I learned from an ancient wizard: “Inverse feedback reduces gain, noise, distortion and OUTPUT IMPEDANCE and raises input impedance.” Grid current can be drawn without excessive distortion from the driver stage with the inverse feedback the way I did it. Due to the low impedance of my design, I only needed 270K swamping resistance across the secondary of the driver transformer. Tim uses a lower resistance to load the stock driver transformer to tame some of the nasty supersonic peak and swamp out the load variations of the grid current. This replacement transformer is only $25 and is commonly available from multiple distributors. This also allows a push pull stage, eliminating second harmonic energy from the driver distortion. The driver stage is the ONLY stage that uses a cathode bypass capacitor. The low frequency response using a 1000 uF capacitor across 2K is sufficient to pass even low frequency energy from severe over adjustment of the clipper stage without canting of the waveform.

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I wanted to maintain the clipper function. You may debate the wisdom of this, as I discuss later. It is essential to retain the excellent low frequency response provided by this 20A14 transformer to prevent canting of the low frequency square waves coming out of the clipper if you wish to enjoy the full benefit of its operation. When using low level speech clipping, it is essential to reduce excess low frequency response in the stages preceding the clipper and get the stages following the clipper as close to DC coupled as possible. This criterion is generally NOT observed in transmitters of this era such as the Apache. The Apache uses coupling capacitors and a driver transformer which are inadequate to use the clipper properly, causing its “scratchy Apache” sound. The clipper, which is an exact copy of a circuit in Terman Radio Engineer's Handbook, is not the cause of the problems at all. Heathkit's defective implementation is the true culprit. When using the line input with outboard audio chains, you will appreciate the 20A14, which CAN drive the 6146Bs into full class AB2 and still have good frequency response without running 1000V on the plates of the 6146 modulators.

Here is the stock audio before modifications.

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Here is the completed work with the small added clipper board.

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Many people remove the clipper from their rig. They lose the over modulation protection afforded by the limiter. It is better to make the limiter work right. My design does that. The limiter (clipper) is solid state diodes on a small circuit board. This frees the socket used for the 6AL5 for a 6AV6 amplifier tube for impedance matching and gain and circuit design flexibility. I found that increasing the resistance of the pot and another resistor noticeably improved the waveform in the limiter. While the Johnson values are the same as common handbook circuits, I found my mine seemed to work better. Driving it hard makes clean looking square waves. The original circuit looks terrible and depends on later filtering to reduce that. W8JI leaves the clipper in and recommends shorting one of the diodes with a capacitor if you want to only limit the negative peaks and allow upward modulation to 130%. How he achieves this upward modulation percentage without work on the output stage to make it work in AB2 or gets low distortion output escapes me. I felt that 3 to 6 dB of gain compression would provide better average modulation level punch than the asymmetrical modulation, which vintage receivers do not tolerate well. Synchronous detection will love the upward peaks. Everyone has their own solution; just because they differ does not mean that one or more of the approaches is wrong. I present my reasoning here, and the alternatives to my approach; you are free to explore options. In practice, no one seems to complain about smaller levels of clipping. It just prevents splatter. Once you exceed 10 dB, people do not like the sound for casual local ragchewing, but it does help some in bad conditions. 18 to 24 dB will likely get you a “military sound” audio report, and the EFJ manual tells you that. Excessive use of clipping or any nonlinear compression techniques causes "intermodulation distortion", a gravelly sound. This results from harmonics and mixing products between all the fundamentals and harmonics contained in the original voice signal. I am sure that you have heard over processed SSB stations, especially trying for a contest mode signal. Even properly done, it gets the job done, but not nice for rag chews. Exercise common sense and moderation in all things. If you do not want to use the clipping function, turn down the gain control, don't hack it out.

Refer to my article on splatter.

For more authoritative information on frequency range for voice communication and optimum clipping levels, consult the Radiotron Designer's Handbook. It is out of print, but you can find a copy for about $30. It is definitely a good resource.

AUDIO BANDWIDTH CONSIDERATIONS

If you want more high frequency response, adjust the values of the modulator secondary shunt capacitors as well as the small cap across the phase inverter. My values were checked out by a local friend with a flex radio and show an upper limit of 3.5 KHz “on the air”. Vintage receivers like the HQ170 and 180 as well as the SX100 and 101 are not likely to hear much higher than that. You can tap into an HQ170 or 180 at the 2^nd IF of 455 KHz and get a hi-fi signal under good conditions, but that is another story. Under optimum conditions, with no band crowding, you can get away with running a wider signal. One option is to put an “old school” high level pi network LC splatter filter in a box mounted to the back of the Valiant cabinet plugged into J8. A second standard plug with only jumpers would be on hand to allow wider bandwidth. Use adequate insulation and safety precautions. These are deadly voltages and may contribute to arcing problems as I discuss in this article. I may write this option up later, or get back to me if you have success with it. You could also mount the capacitors used to “build out” the mod transformer in the J8 mating plug, possibly with multiple plugs available for quickly adjusting the high frequency response of the system.

All other stages in the audio chain have unbypassed cathode resistors. This results in low distortion from each stage owing to the inverse feedback from this configuration. Distortion in each 12AX7 stage can exceed 2% without inverse feedback. Most designs I have seen employ cathode bypass capacitors, which do not take advantage of this improvement in the low level stages. This approach has lower distortion and noise resulting from the inverse feedback. A magic incantation I learned from an ancient wizard: “Inverse feedback, reduces gain, noise, distortion and output impedance and raises input impedance.” Use the 12AX7 as I show with no cathode bypass capacitors. It has more than enough gain with a good microphone.

If you want more lows from the preamp, increase the two coupling caps from 0.002 uF to 0.0033 or 0.005 or even 0.01 uF for the second stage cap. Keeping the first stage capacitor smaller and the second stage capacitor adjusting larger adds some warmth lows but still retains some presence rise that helps brighten the audio and increase intelligibility. Remember, if you employ the clipper, it will sound muddy if you run a lot of low frequencies through it. The values shown worked OK for my voice and my Dee Ten Four mike, without hum in the output. The important tradeoff is that if you run excessive low frequency energy through the clipper circuit and crank it, the intermodulation distortion increases and destroys intelligibility and sounds gravelly. Do not exceed 10 dB of clipping ever. If you really want wider bandwidth, you should use the line input anyway. I have both available and adapt my use to prevailing band conditions.

Many recommend a 10 Meg resistor in the mike circuit. I found that hum was excessive in my rig with a D104 and higher values, so I stuck with a 3.3 Meg and smaller coupling capacitors, especially in the input stage. Encasing the resistor in shielding is said to help. Use shrink sleeve to cover the resistor and cover it with grounded braid. I do not have a deep voice, so I did not need to have extreme low end performance in my solution. Experiment with the two 0.002 uF coupling capacitors in the 12AX7 stage to add lows. The mike wire passes by the filter choke and transformer, and is in a harness bundled with AC wiring. Possibly using DC filaments in the audio section would help, but I did not try it. I considered removing the MAN – PTT switch and placing the mike connector there at one point. This rig had a custom paint job. It made no sense to compromise its appearance. I have made no changes above chassis that detract from its appearance.

The best way to avoid this entire problem is to use the W8JI D104 FET mod to drive the Valiant with a low impedance, which eliminates hum and frequency loss. http://www.w8ji.com/d104_to_low_impedance.htm

The driver transformer will carry a lot of lows, but remember that the output modulator iron is not designed for this and a lot of current flows in the winding trying to produce those frequencies. When I had feedback that contained the output modulator transformer, I noticed frightening amounts of plate current trying to maintain a flat frequency response for the lows. Keep this in mind if you use the line input jack. It wants to see about 0.5 to 1 V of audio.

Extensive square wave testing resulted in the values in the feedback network and B+ decoupling capacitors.

OTHER REPAIRS AND MODIFICATIONS

All the power supply filters were beefed up. In addition, the Bias and Low B+ supplies were solid stated. Many people claim to reduce transformer heating by just slapping a solid state diode in place of a high vacuum rectifier. True, you save the filament current. However, you get very high peak charging currents owing to not accounting for the effective series resistance of the the tube diode. This causes excess heating of the power transformer to the high peak currents. The DC output voltages are all out of spec high. Often this damages the marginal drive control pot and the Chernobyl Resistor in the VFO. Avoid this. In the circuit diagrams, I provide the correct forward drop as calculated from the RCA tube manual data. Examine the process as explained there and you can create your own solid state replacements for high vacuum rectifier tubes of any type, the right way. Later, I may provide a separate file of vacuum tube rectifier replacements as I develop them.

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The green power indicator is not very bright. I provide a #47 bulb replacement LED in the schematic section. The average value of 0.318 times the peak value comes from circuit theory and is used in common older VOM circuits to calibrate their AC ranges when employing a half wave rectifier for an analog meter. You can use this same technique, with adjustment to the resistor value, in other applications. If you use something other than the Radio Shack LED specified on the schematic, you will be able to adjust the resistor for your part using the math on the schematic. In addition, the Radio Shack 276-0024 LED has a 130 degree viewing angle and might work well to illuminate the VFO dial if properly mounted; I did not try it yet. It also may find a home in my HQ180. Look at the schematics and calculations and you will see how to do it.

I also replaced the internal Low Voltage and Filament Transformer fuse with a fuse holder that is accessible from outside the cabinet. A tube saver thermistor and a Metal Oxide Varistor (MOV) complete the AC line improvements. This affords some protection from surges and start up current. You can also use the 5 volt rectifier winding to reduce the primary voltage to the low voltage transformer. The winding for the 866s is only 2.5 volts and not worth the trouble of stealing it. Also, the commercial solid state replacements for the 866s behaved very strangely without the filament voltage. I suspect they use the filament winding with an scr type circuit to fire the rectifiers at zero crossing. This seems to result in no "thump" when the plate supply is first turned on. I did not pursue it further. Two essential guidelines I operate by: "If it ain't broke, don't fix it. If you tinker with something long enough, you will break it." The whole high voltage section, including the 2.5 V filament winding is something better left alone if possible. Use 3B28s to replace the 866s. They have very low forward drop and work great.

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I retained the original fuse plug, but I run a hefty ground lead to the cabinet and am aware of the risks. Putting a fuse in the neutral of the AC line is not a good idea without a good ground on the rig. Finding a place to mount the proper AC fuse for the rig is problematic. I may revisit this in the future, if I can find a spot on the rear apron. In that case, a three wire grounding plug is going to be installed. You can mount the fuse holder where the SSB input is, but I use that for my frequency counter.

If you have not done it, replace the Chernobyl Resistor in the VFO. This is the 18K carbon resistor in the screen and regulator circuit, R3. I do not recommend removing the VFO from the rig due to possible damage to the unobtainium VFO shaft coupling. I have a pictorial tutorial showing how to remove the side panel near the VR tubes and mount the new wire wound resistor below the chassis on a terminal strip held by the VFO mounting screws. Don't make it harder than it is. See my expanded article on the VFO.

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Before you reassemble the transmitter into the cabinet, there a three more VFO related items you must correct. This appies to the Valiant and the Ranger, or any other E. F. Johnson transmitter with an internal VFO.

First, you must properly ground the Plate Tuning capacitor for the final amplifier. The metal shaft for tuning passes right by the VFO. On 40 meters, all the RF stages operate on the output RF frequency, or as we call it, "straight through". This results in the VFO frequency changing or "pulling" from the frequency you set in zero beat mode at low power. The fix is very simple: replace the fiber washers between the Plate Tuning capacitor and the metal chasis with metal washers of the same thickness. This idea comes from W8JI. https://www.w8ji.com/johnson_vfo_chirp_jump.htm He shows in photos exactly how to do this. It is a very simple modification that you should do while you are in there. I left the buss wire in place and grounded the capacitor directly with the washers and it worked for me.

A second improvement you can do to get the "spot" frequency to match the transmit frequency is to put a jumper wire on the "spot" switch. This wire should key the exciter stages (with the Plate Power switch OFF). I do not have the schematic on how to do this, but if you trace the wiring, it is clear. The "spot" switch only keys the VFO as wired from the factory. You have to wire it so it keys the exciter stages as well, just as it would do it if you pressed a key plugged into the key jack.

This modification works by having the same load on the VFO as it would during transmit.

The third important fix is in the alignment of L17. You probably have to recalibrate the VFO, since you disturbed its wiring while replacing the Cherynobl resistor. You should also go through the rest of the alignment process. One source, I think WA2QIX, I cannot remember who, found that L17 should be unscrewed all the way up instead of peaked for maximum drive. Adjusting by this method cures the VFO FMing during modulation. If your signal is observed on an SDR or spectrum analyzer, it will have non symettrical side bands. That should not happen with proper AM. This simple L17 alignment tip will reduce FM or phase modulation, cleaning up your signal.

I have also heard from multiple correspondents that adjusting L17 all the way to the top also reduces chirp in the E. F. Johnson Valiant. Besides curing the FM on top of AM problem, this apparently is a proper fix for some sort of loading problem. Perhaps if the VFO were located outside the transmitter cabinet as it is in the Viking II, this problem might not be as severe.

WA1HLR recommends placing a 5K 5 to 10 Watt wire wound resistor in the LV B+ side of the drive control R51. I strongly recommend this along with the rectifier design included in the schematics to avoid excessive power supply voltage. He recommends another 5K in the ground return side. I found that 160 Meter drive could not be reduced to spec with this value. Maybe my tubes were newer and had more gain. Try a lower value fixed resistor if that is your problem. My rig arrived blowing fuses due to a bad drive pot shorting the B+ to ground. I did not have a 25K pot in my junk box. I used a 20K pot with 22K in the B+ end and no resistor in the ground end, and it worked fine for me. Drive was OK on 10 and 15 meters with this configuration. I super glued the extra resistor to the back of the pot as shown in the photos so it was not just flopping around trying to short out. Timtron is correct in pointing out this chronic problem; I just had to improvise with what I had in stock. If your drive pot has not yet failed, do this before it does. As an exercise, do the math. The pot is running at its full 4 Watt rating under ideal conditions in the stock Valiant. With high line voltage or improperly done solid state power supply, it gets worse.

Refer to this page: Drive Control.

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Removing a bad drive pot or clipper control comes with its own problems. There is a nut between the front panel and an L bracket mounting the control. This allowed the rig to be operated without a front panel for testing. To avoid removing the front panel and the extra labor and risk (to the VFO drive), I use the following technique. Remove the knob and front panel nut and washer. Remove the low level tubes from the modulator near the control. Remove the wiring from the control. If the control cannot be unscrewed from the back easily, grasp it firmly with pliers (its bad anyway, so crushing it slightly won't matter). Use a thin screwdriver to keep the captive nut turning as you back the control out. Slide an old short pencil in the front of the hole to keep the nut from falling down inside as you remove the bad control. To keep the nut in place, insert the new control as you withdraw the pencil. You can either allow the old nut to remain or remove it and replace it with a flat washer. Something is needed as a spacer to avoid dimpling the front panel when you tighten the front nut as you reassemble the rig.

RF TANK CIRCUIT MODIFICATIONS AND REPAIRS

One important thing that I do for the RF deck: SOLDER the connections in the plate tank coils. The screws may loosen and all hell can break loose intermittently if you do not. An excessive amount of solder is not required. See the picture of what I did.

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The Valiant One schematic shows a 2000 pF for C37 coupling the 6146s to the tank circuit. My Valiant One had 500 pF. The Valiant 2 uses 500 pF. WA1HLR recommends replacing the lower value with 1000 pF for better efficiency on 160 Meters. It does not seem to contribute to any condition which might cause circuit failure if you leave it as is. If you do not use 160, maybe you can leave it alone. My rig had screws mounting C37 that would not budge, so rather than breaking something, I just let it be. Maybe sometime I will solder in a 500 pF in parallel. Power output is down about 10 – 15 watts on 160. This might help it.

On the other hand, EFJ does not maintain the circuit Q properly on 160. This might account for some of the power drop off. To do it right, the 160 coil L39 would be reduced and another padder cap like C39abcd would have to be switched in. After modification, would the tuning range of the existing variable C8ab be enough to tune the whole 160 Meter band ? More modifications to the band switch and coil winding was not justified in my opinion at this point. Increasing circuit Q might improve harmonic suppression and output. If you use the Valiant on 160 with a high impedance or multiband antenna, be sure to use a tuned link or "low pass" style antenna tuner. The common C-L-C transmatches on the market are a HIGH pass, which afford no harmonic suppression.

The Valiant is in no way inferior to any other rig of its time. The Viking One and 2, DX100, and others all just throw a padder coil in to get on 160 without proper attention to circuit Q. (I put an Apache on 160 with the correct circuit Q and the addition of a 100uH coil in series with the stock grid driver coils. The Apache VFO operates on 160 and 40 and multiplies into the other bands exactly like the DX100. Incidentally, standard 6146s in class AB1 might be a good substitute for the 6CA7s in the modulator. The 6146 plate impedances might "bolt up" just fine to the stock Apache mod transformer. The 6CA7 is way outside its specs on plate voltage in the Apache, and the screen pin arcs to the plate pin on the socket and tube base as happens commonly in guitar amps. I may write all this up some day in a separate article.) None of these rigs seemed to result in OO reports when using a coax fed low impedance antenna with good SWR. Direct feed (without a tuner) of a high impedance or high SWR antenna will likely be risky, in my opinion, regardless of EFJ claims to matching 600 ohms direct from the radio.

I also put a 30K 2W resistor across the RF output terminal. If you use an antenna or tuner that does not provide a DC return, voltage can build up and destroy the output fixed mica capacitors or coarse loading switch contacts. Normally, a 2.5 mH RF choke is used in later designs after they discovered this problem which also afflicts the Viking One and Two, DX100 and Apache as well as other rigs. Self resonances can occur in RF chokes, so I just threw a resistor in to solve the problem without going into extensive testing with a grid dip meter and so on. NEVER change the settings of the band switch or coarse coupling switch at full power. Load the rig in CW mode, let up on the key, change the coarse loading, then key up and complete the adjustment using the FINE loading only. Do not just fire up in AM and let the plate meters (including the modulator) fly where they wish as you madly tweak everything. Sooner or later, something unobtainium will fry.

CONNECTOR ANNOYANCES

There are two connector annoyances that Johnson inflicts on us. First is the @#% antenna relay connector. Buy a good quality two wire extension cord to be cut in half. I put the socket end of an extension cord outside the rig and pass the wire through the AC cord grommet. Solder the wires to the "crystal socket" terminals INSIDE THE RADIO. I use the remaining plug end of the extension cord from the first step to wire the antenna relay coil. Solved.

Second is the mike connector. The LV B+ is used on the PTT circuit. If you plug a mike in with the power on, the two connections can make before the ground connection. This passes DC through the mike element, destroying it instantly. Fortunately, my grandfather worked for the Erie Railroad and could go a half hour with profanity and never repeat himself, and I have learned that method of stress relief for this sort of occasion. I use a 4 pin standard mike connector that Radio Shack stocks. This provides a good connection for the ground lead. Use BOTH of the extra pins for ground if you are paranoid, but this will make the mike incompatible with other rigs.

I also put a "catch diode" to suppress the spikes generated by the coil of the relay. The diode connects to the COIL of the relay, not any of the contacts or AC or keying circuitry. This diode only conducts briefly when you unkey the radio to "eat" the inductive field collapse. The BANDED end (cathode) points to the + supply side. The anode goes to the PTT side of the coil, which is grounded by the plate switch or the mike PTT line. Use a meter to double check the wiring in your radio matches mine. This is not completely necessary, but reduces sparking on the mike's PTT contacts. It would be better to rectify some of the filament supply and use a low voltage relay.

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OTHER ITEMS YOU MAY WANT TO ADDRESS

A low voltage relay, or better yet, a solid state relay for the plate transformer primary and a transistor to drive the exciter keying would be even better. If you do this, be sure to retain the safety links in the VR tube sockets to prevent activation of the HV B+ with the VR tubes unplugged or you may regret it. Your will to modify and parts supply will govern whether you want to pursue this.

The keying line is in excess of 200 volts can bite you or destroy your keyer. Adapting the circuit to be more like the common Johnson modification to the Ranger, which has lower keying voltage, might be a good idea. Alternatively, a high voltage transistor to isolate the key jack might be another approach. The later keyer in the Ranger used lower bias voltage. You can reverse connect a 12 Volt filament transformer from Radio Shack or your junk box to get the lower bias voltage for the keyer.

I also put a wire jumper on SW4A mode switch. This allows the morse key on the rig to key the exciter stages in all modes. You now can spot with your crystals or the VFO. It allows me to use my frequency counter without putting a signal on the air. It saves wear and tear on the VFO-crystal switch or AM-CW-SSB switch just to get on frequency. If there is any jumper on the J2 Key socket to short the connector when no key is plugged in, remove it or the circuit will always be closed.

I set a large muffin fan above the finals to cool the cabinet. Some cushioning prevents cabinet scratches. Not as effective as cutting a 4 inch hole in the back, but it does not damage the unit as a collectible. I also put some small pieces of wood under the feet to raise the cabinet for more airflow into the bottom chassis. Long "Old Buzzard" transmissions still leave things nice and cool.

One of the high wattage 12K resistors is just flopping on its leads. Normally this hangs off one of the unused tube socket pins of the 866 rectifier. Mount it to the chassis, but use insulating washers. Or add a terminal strip.

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Heat sink plate caps help, see the pics. These are designed for transistors, but they seem to work well on the tubes too. The larger commercial plate caps of massive aluminum are nice, but they should be painted black for best dissipation. Also, the crowding around the RF choke and copper strap makes them difficult to fit. Even these small heat sinks make the plate seal noticeably cooler after a long transmission.

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At the expense of being concise, I included some thoughts on ideas that I discarded. This is to save you the frustration of trying them out and finding out they do not work, the same as I did.

Everyone has their own solution; just because they differ does not mean that one or more of the approaches is wrong. I appreciate them taking the time to put their ideas out there to help others. They risk someone disparaging their work when they do, but do it anyway. I present my reasoning here, and the alternatives to my approach; you are free to explore options. By explaining my methods, even if you do not do any modifications, it may provide some ideas to begin your own work. I hope you found something useful.