Johnson Valiant

[W2VW]

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.

[ke7trp]

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

[KM1H]

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

[ke7trp]

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

C

[WA5VGO]

Only a few volts on mine.

Darrell

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

C

[The Slab Bacon]

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  

[W3RSW]

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.

[WA1GFZ]

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

[The Slab Bacon]

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.

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!!

[The Slab Bacon]

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

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

[ke7trp]

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

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  

[WBear2GCR]

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

[WA1GFZ]

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

[ke7trp]

Good point from a guy with "perfect" audio

C

[W2VW]

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

[WA1GFZ]

agree Dave.

[The Slab Bacon]

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

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!

[VE3AJM]

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

[Jim, W5JO]

If you want to have fun with the Valiant and get more out of it and try different things to optimize performance..why not?

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

[W2VW]

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

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.
 

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.

[Ed/KB1HYS]

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]

[W2VW]

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.   

[w4bfs]

........
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

[W2VW]

........
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...........

[The Slab Bacon]

[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.

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.