The AM Forum

I just picked up a Valiant this past weekend. After replacing the electrolytics and undoing some mods for a sideband adapter it seems to work as it should. The 866's don't seem too healthy so I think I'll look for some 3b28's. I plan on doing some audio mods, although I haven't decided how far I want to take them yet.

I've read the insulation on the HV rectifier filament wiring can be insufficient on some of the Valiants. This one has cloth covered wire coming from the transformer to one of the rectifier sockets and from there it has what looks like cheap 20ga hookup wire to the next rectifier socket. I can see how that hookup wire could be a problem, but what about the cloth wire?

Solid state the HV rectifiers and remove the heater connections and never worry about it again

I'm with Frank. The whole rectifier filament wiring has to be insluated for high voltage. Even inside the transformer.
You can lose that transformer to an insulation failure.
Solid state is a proven mod.
Want pretty colors get a lava lamp.

I agree with the others, solid state the HV rectifiers.  Even with proper wiring other bad things can easily happen, for example if you bump a microphone with a locking PTT button while the Valiant is off then as soon as the LV is turned on the plate supply is also activated and although that is never a good thing it is particularly bad with MV rectifiers since the rectifier cathodes are not up to temperature.

Other standard things to check on a Valiant are to replace the bias rectifiers, the undersized VFO VR tube dropping resistor, and seriously consider not having both sides of the power cord fused.  Neutral should never be fused.

To prevent breaking the oddball insulating coupler on the VFO shaft the set screws should always be loosened prior to turning the Valiant upside down.  If the VFO tuning is not smooth, you need to clean the ball reduction drive and re-lubricate it.

Then take the extra 5 volt winding and put it in series with the LV transformer primary. Properly phased will drop the heater voltage closer to 6.3 and the transformer will operate a lot cooler

All Good advice. But, do what makes you happy, just know the risks (ie: keeping 866's looks cool but can flashover etc). I really liked the 866s, but ended up going Solid State after the filament leads arced to ground.  IF I had checked that when I recapped and repaired it, I would have run heavily insulated wires before powering it up.  (A clue that there was a problem should have been that the previous owner had installed the mains fuse holders conveniently on the front panel!!)   

Solid stating the power supplies (both Final Plate, and the audio chain HV) isn't a bad idea, put in a dropping resistor to get the volts back down to where they aught to be.  Change out the filter caps, a bit larger is good.

Audio chain changes?  Well, some folks would have you tear out the whole thing and start fresh. I've found that going through and bypassing the clipper circuit and the audio filter and changing some of the component values to optimize what you have worked pretty good.  Some folks like HiFi, which the Valiant ain't, but I don't think you need to blast the whole audio section to bits either.

Timtron has a good writeup on the Valiant audio section, http://www.amwindow.org/tech/htm/valiantbytron.htm   

You can do all or some. Your call.   

Probably the best thing about a Valiant is that they are not Rare or Unique transmitters, so you can tinker to your hearts content. 

I just changed the rilter in my V2 CDC to a choke input filter. HV I left alone. 6146s like 760 volts.

Thanks for the replies. I'll pick up some diodes and solid state the rectifiers.

I have opened up the VFO to check things out, and it looks great inside. There are no signs of scorching or damage from that resistor, but I'll go ahead and replace it with a higher wattage resistor.

I don't have any problem modifying this thing as long as I'm not drilling holes. The previous owner must have been a smoker. There is a yellow brown film all over everything, but it looks like it will clean up well.

I've read the article by Timtron, and also this one: http://www.amwindow.org/tech/htm/valiant/valiantmods.htm

I assume the latter would have better audio quality since it eliminates the driver transformer? I don't expect this thing to sound hifi, but I sure would like to make it sound a little better than it does now.

Your going to get alot of opinions on the valiant. There are alot of really knowledgable guys here.

Here is my take.  Many of this is obvious and could be a waste of time to read.  I have three valiants now.

Insulate the wires for the rectifiers. I got an idea from a member here about silicone hose. This works great.  Slip this over the lines and they will not arc.  You could still arc inside the trans but I have never had that happen.

3B28s work fine. Solid state plug ins also work great.

I would leave the regulators and screen volts alone.

Do the Mic amp hifi mods.

Change the Choke bypass caps.

If you have the small Door knob cap, Get a larger one. Some valiants had a very small sized cap here. Later, Johnson updated this to a larger cap.  I like 1000PF here.

I like the clipper.  No reason to rip it out if you are going to use a D104 ect.  I have run both ways.  I just like it functional. I am in a neighborhood and running spotlessly clean is very important to me. I use a EV636 mic and like to turn up the audio and lean back in the chair. Then I can bring that clipper in to just keep the audio from flat topping.  I get some compression and some limiting. 

Change the Grid resistor on the mic input to match the mic you are running 2meg for D104 seems fine to my ears.  5Meg works also. 

Order new Clarostat Drive control and audio control pots now and just replace them.  They will fail.  Every damn valiant I have come across or owned has a scratchy worn Audio and Driver pot. They are to small. Get higher watt units. They fit right in.  I purchased mine on Ebay and the guy sent them right out.  4 watt, 25K I think.

Do Change the VFO resistor to higher watt.

Do use a solid state plug in for the LV rectifier.  It runs hot and if that tube fails, it will take out the DC choke. This happened to me and lucky for me, my fire alarm came on to wake me up from a sunday nap.  Ever run down a hallway at full speed with a Valiant that is pouring out smoke? 

Do put a three wire cord on and Drill the hole for a proper fusing.  Valiants used the fuse plug and lots of times that cord has been replaced with NO fuses.

DO replace the Parasitic Resistors in the modulator plate cap leads.  They fail if the modulator oscilates. Just put new ones in now.

Do take a tooth brush and Deoxit to the Course loading switch and band switch and SCRUB the ceramic wafers. Any carbon tracks around the rivits WILL arc and you will have to take the thing apart gain to fix the damage.  Spray it, Soak it 15 min, Scrub away until all the contacts are nice and clean. Rotate the controls.  The reason this is a sore spot is people HOT switch the course loading control and create carbon tracks. After doing this, I never have any trouble with this major valiant sore spot.

Do Adjust and tighten the Cam arm on the bandswitch. This arm switches in capacitance. It needs Lock tight and some lube on the cam. You will see what I mean. I have had to take valiants all the way apart because I did not use lock tight and this came loose and jamed up during a band change. PITA.

Thats it. Thats all I do.  Its not a Super hifi valiant. Its just a valiant that works and sounds good.

 

Change the screen resistor in the VFO to a wire wound power resistor. It is a weak link in the design. I used a 20k 10 watter if I remember. The old resistor measured 45K but still worked. Stock value is 18k

Thanks for the help.

I just happen have a pack of 20k 10watt resistors here so one of them will end up in the VFO.

As far as the audio mods go, I'm probably going to get rid of the interstage transformer and build the phase splitter. The 6146s will get replaced with a pair of 6DQ5s.

Some other projects got in the way, but I'm back on this thing again.

On this phase inverter schematic: http://www.amwindow.org/tech/htm/valiant/audio.htm why is the audio being fed to the screens?

It is an error in the drawing.   The control grids should be connected to the phase splitter through the 510 ohm resistors, and the screens are connected to the screen supply through the 1000 ohm resistors.

Just a note on changing the VFO resistor, mount it Outside the VFO enclosure.  They get hot and can cause drift etc.  I simply mounted mine in a cable clamp on a standoff just outside the enclosure with stiff wire extending the leads.  No problems.

If you use the right size resistor it doesn't get hot. Both my 122 VFOs are quite stable with the resistor inside.
not a lot of WOPs involved here.

I think the 0A2 fails and overcurrents the resistor. Put a new one in while you are there and check compents.  I used to mount the resistor outside.  I now think that inside is the way to go for stability.  My 2cents.

C

I replaced the VFO resistor with a 20K 10W and put it inside the VFO. So far it seems to be stable.

Last night I built the phase splitter. It still needs some work, but it sounds much better. There will also be a pair of 6DQ5s going in later.

The two valiants that really stand out to me had the phase splitter mod done.  I am sure you will be happy with it Chris. 

C

The 6DQ5s are in place. I'm running 150v on the screens and idling them at about 50ma. It is still not quite making 100% positive, but it has no problem making 100% negative. Switching audio phasing made it worse. Looks like I still have more work to do, although it sounds MUCH better than stock.

Another great site for ideas and circuits to improve the audio from 100w class AM transmitters including the Johnson Valiant, is K1DEUs site.

http://www.hamelectronics.com/k1deu/pages/ham/transmitters/am/pages/universal_speech_amplifier.htm

John used 811as in the modulator, used a quasi cap input power supply modification for higher B+ voltage on the modulators and changed the audio driver to drive class B modulator grids. I would think that the 6DQ5s would also work well in those applications too.

Al

Thanks for that link Al. Interesting stuff

This thing will now do 100% positive running the final at 300ma, but it is a struggle. Has anyone run 6DQ5's at 1100v?

Thanks

Chris,

  Sounds like you have made a bunch of changes. Any chance you can collect your notes,, and sketch a schematic? If so, post it here for the gang to look at.

  In many cases when we get up around 100% modulation with vintage gear, the modulation linearity of the RF PA stage shows its ugly head. Often times the RF stage G1 bias is incorrect, or the screen grid is either over or under modulated, or modulated out of phase with the plate, etc. Your 100% upward limit could be in part due to the PEP limitation of those three RF stage 6146's for reasons just mentioned, or even due to one or more of them low on emission reserve.

Jim
WD5JKO

Hi Jim,

I built the phase splitter shown here: http://www.amwindow.org/tech/htm/valiant/audio.htm and have replaced the 6146 mod tubes with 6DQ5 by rewiring the socket and lowering the mod tube screen voltage to 150v. There wasn't much difference between the 6DQ5's and the 6146's. I tried swapping out the finals with another set and there was no change. The bias on the finals is set to -70v.

The Valiant can't modulate over 100% positive due to the modulation transformer ratio and rf and modulator on same voltage.

The 811 on higher B+ idea is one workaround.

There are 6DQ5s in the Valiant II I own. It was mod'ed by Dave, KE1AX (iirc, not sure I have the call correct today). The mod iron MAY have been changed, not sure. But it has the 3 diode limiter and definitely does over 100% positive. I have not checked the B+ on the 6DQ5s. They swing major monkey on the mod current. Assuming the mod meter is still calibrated, easy to pin the meter on peaks.

This may or may not have Heising modulation, not sure, have not traced the circuit. I only had to make some repairs and run it. The mod deck has been bulldozed and changed totally. I think HLR had a say in what was done, if I recall what I seem to think I heard back when this was all going on.

The one thing about the Valiant is DO NOT KEY IT WITHOUT A LOAD!! That will arc the rear wafer on the bandswitch, almost for certain. It does on mine, don't know about any others... I would like a wafer on the rear with contacts the size of Cincinnati!

My 2 cents worth...

                       _-_-bear

May have the autotransformer connected mod A.K.A. turbo mod.

I have three valiants.  They will all JUST hit 100% if there are solid state diodes installed in the PS.  I dont think you are going to get one much over 100 without changing the iron as has been said here already, so I think swapping the mod tubes was pointless. 

I also do not think anyone is going to notice if you now spend the time to get the valiant up over 100 percent.

What you can do if you must have more peak to carrier ratio is to simply change the screen resistor on the finals.  You can alter this so you have 100 watts of carrier and then, you will have 115 to 120 pos or so.   I like the carrier big so i have removed this mod in the one valiant that had it installed.  I dont like the idea of loading the rig down much lower then the 330ma but you can certainly do that also Chris.  Load to 275 and try it.

Another thing I want to point out is that you can adjust the grid current (drive control) so that you get max modulated positive output on your scope or PEP meter.  This has a big effect.  I recomend that you DO NOT turn the Drive control as you are keyed and or modulating the rig, If you do, You could smoke that 60 year old Drive pot.  There is a point where the Grid Drive will produce the best peak output, Leave there or back of a mil or two.

The last thing is to slowly rock the plate tuning.  On some valiant its nearly impossible to get the neutralization perfect and its likely going to produce the highest modlated output off center dip a touch.  Some have removed a plate on the Neut cap in order to get the rig better neutralized.  I see that was done on one of mine in the past. 

C

The difference between a 866A and a string of diodes is under 10V; I dont see that doing much for the modulation index.

We have covered this before with data.  Its a huge increase on the valiant carl.  The Drop is not 10 volts.

C

Only a few volts on mine.

Darrell

Wah, Wah, Wah  :'(  :'(  

 It's not just the total peak modulation percentage, but the average modulation and modulation density! !   ::)  ::)

Higher average modulation level will sound better (and louder) than just having high positive peaks. A little compression can go a long way  ;)

Frank, how ya doin' over there?
About time to fire up the WFD net on '33 now that nights are coming earlier.  I should be able to get over the mountains in about a month. 
I wish DST had never been instituted in a lot of ways.

Taking out all those stupid rectifier tubes makes room for modifications and reduces heat and transformer load.

thanks, Rick. I plan on the same, prolly a few more weeks before condx improve a little more. I fired up 2 Fridays ago and the onl one there was Ralphie. Condx were real bad!!

Frank,
         There are more recipes out there for Valiant mods than Grandpaw's secret BBQ sauce! !! !

Your 100% correct :)  Thats why I dont worry about trying to load the rig down, like you suggested in an earlier post Frank or doing the Screen resistor mod.  The johnson engineers where not dummys.. Most people rip the clipper out when run correctly about 6 to 8 DB really helps get the avg up.  I have heard many a Valiant TROMP some of the 1000 watt Carrier BC rigs run by people on this forum with all that FY%IUY$  bass cranked in :)

C

I load mine to only ~200ma plate... it may well have the turbo mod. If an when it self destructs and I have to do surgery with the belly up, this may well be discovered...

                   _-_-bear

6DQ5 should make more clean output voltage swing without distortion due to lower screen voltage.

Good point from a guy with "perfect" audio :)

C

Under loading or reducing screen voltage on a Valiant with factory connected mod iron is like putting a band aid on a gunshot wound.

agree Dave.

Depenz on how you look at it. I have loaded mine only to 275mA (about 100w out) for the last 15 years with no problemz. All I did to it was bypass the crappy clipper stage, and fatten up the coupling capz to something a little more reasonable. I run a little compression from an outboard speech processor and everyone always sez it sounds quite good!

Loading it to 360mA really saturates the undersize mod iron and killz the audio quality. No one is going to be able to hear or see the difference between 100w and 140w except in the quality of the audio.

You cant take szht and make ice cream!! A valiant is NOT a broadcash rig, so why go through all of the work to re-invent the wheel when it is already sitting there in front of you! ! ! ! !

The Valiant is a terribly under designed P.O.S. With only 650v on the plate supply, and a really undersized mod iron, you are fighting a losing battle from the beginning.

But............. with a few small mods and a little conservative operation, they are a great workhorse!

If you want to have fun with the Valiant and get more out of it and try different things to optimize performance..why not? It may or may not work out for you, but you'll gain experience at modifying a tx and the audio. That what ham radio is all about..the autotransfomer/turbo mod for the mod iron will help.

You may also have another modulation transformer with a better turns ratio/power handling capability, that would work better too.
I would triode connect the 6DQ5s in the modulator if you're going to use them, and not have to deal with screen voltage. More linear and cleaner audio from a triode. Connect the stock mod iron as an autotransformer, and change the audio driver to a single ended triode like a 6550, with a suitable new driver transformer, bypassing the low pass filter/clipper for sure, and go from there. It'll all depend on your knowledge/imagination and the available parts/iron etc that you have on hand and what you're trying to achieve with the audio.

Al VE3AJM

Why not just home brew something?  A valiant is what it is.

The problem is under loading in order to give the modulator a break is not helping.

The mod xfmr ratio is too high and a higher load impedance (less I same V) of the 6146 trio is headed in the wrong direction to provide headroom for the mudulator.

Ok, how about simply pulling one final tube out of the Valiant, A pair modulated by a pair? Then adjust the expected current values to reflect two tubes...   Sure that'll drop the output quite a bit, but you'd have a better ratio of modulator power to RF power, No?  The output network could probably still work, although not near the expected settings. 

[now donning asbestos suit]

That would only leave you with a neutralization procedure to do and zero benefit.

Taking advantage of a better ratio of modulator power to rf power requires a look at the mod transformer's ability to transfer that power.

Keeping the same final voltage and lowering the current changes the stage's load impedance and also the impedance seen by the modulator in the wrong direction. It is too high from the design and headed even higher by pulling less current.

The situation is similar for people who insist on lowering the screen voltage of a Ranger to give it less output when driving a large linear amplifier. That's the wrong way to do the job and will cost in terms of peak power and unwanted garbage products.   

Interesting ..... I may have missed this discussion .... planning to do this (variable screen V) on several projects .... could you please quantify this a bit more .... I realize by reducing screen V that this will raise both the rf and modulating impedance of the pa stage .... this reduces rf stage efficiency and unloads the modulator .... it seemed to be acceptable since modulator power required would decrease as well

I am building a series modulated ranger using the 4N150 meshfet design presented here on Amfone.net ... if lowered power out is needed then can lower pa stage plate and screen V and retain both rf and modulated impedances or can build a rf pad and throw away extra rf before the linear amp.

What drives the choices is the need to be able to tune the amplifier for best linearity at peak power ... this is generally 4X carrier power and more if asymetrical modulation is applied

Since we are talking about Valiants it is not acceptable. The Valiant needs all the help it can get with the modulator section. Anything done to improve the dynamic headroom of the modulator will pay off.

If you wish to lower output power on a Valiant use a dropping resistor in series with the final plate feed (include the feed to the screen) bypassed for audio with a suitable capacitor OR come up with a way to use the low B+ for the final instead of the high B+ but leave the high B+ on the modulator. Instant audio improvement and now a better choice to drive an AMplifier.

Some folks insist on using a pad because E.F. Jaw and Son sold one years ago. Same thinking as using a store bought dipole or a 43 foot magic vertical. If you like heating up resistors, heat one in series with the final. Again, it must be bypassed for audio.

It's wise to come up with a way to switch to full power for tuning the following linear AMplifier purposes as you say.

The Valiant is a good candidate for a low power driver since the rf section needs a lot of changes to take advantage of an improved modulator.

Of curse we could just complain the rig was not designed to do this and that and just grab another beer...........

Dave,
        I have had this same discussion with many others, many times. all that I can tell you is that with My Valiant, it works for the better. As many times as we have worked, you have heard my Valiant many times. No one has ever complained about how it sounds. When I load it to 360mA it sounds like a typical valiant, at 275mA it sounds quite good.

Under loading changes the impedance that the modulator plates see, but the turns ratio of the iron is still the same. So, lighter loading does increase the impedange that the modder plates are lookin into, but in some cases this works for the better and looks in your favor.

In extreems, too light of a load can kill a transformer, but in this case the loading on the transformer is still sufficient to suppress the transient spikes from the voice peaks.

All I know is that it works for me, and I have been running my Valiant that way for many years without any problemz.

Frank,

Another scheme which may have some merit is to put some additional voltage on the modulators.  I believe currently Johnson only puts maybe 650V on the modulator tubes.  Just adjust the static resting current accordingly for the proper class of operation. You can put quite a bit of voltage on 6146's without any issues. Many ways to do that, but a very simple way is to add a pair of HV SS diodes to the secondary of the Valiant's HV CT xmfr.  Then run those diodes into a large value filter capacitor network.  That should produce greater modulator voltage to easily permit 100% modulation.  The final supply would still utilize the choke input supply so nothing would change there.  They use just a plain hi C filter network all the time in linear amps and the modulator demands would be similar to that.  The key is to have enough C to support not only the peak modulator current but to reduce any ripple component to an acceptable level. My goal would be to keep everything inside and not any drilling and blasting.  An inrush circuit should be utilized in the primary to limit peak rectifier current at turn on due to the added Hi C cap bank.  As long as primary voltage PTT was not used the inrush circuit could be cheap and dirty with a properly rated thermistors although I prefer a relay shorting out a primary inrush resistor after the filter capacitors are charged.            

Joe, W3GMS