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Author Topic: Johnson Valiant  (Read 28853 times)
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Chris P.
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« on: April 02, 2012, 04:01:27 PM »

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?

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WA1GFZ
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« Reply #1 on: April 02, 2012, 04:15:30 PM »

Solid state the HV rectifiers and remove the heater connections and never worry about it again
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W2VW
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« Reply #2 on: April 02, 2012, 04:40:42 PM »

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.
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WQ9E
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« Reply #3 on: April 02, 2012, 06:44:34 PM »

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.
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Rodger WQ9E
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« Reply #4 on: April 02, 2012, 08:25:02 PM »

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
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Ed/KB1HYS
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« Reply #5 on: April 02, 2012, 08:26:15 PM »

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. 
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73 de Ed/KB1HYS
Happiness is Hot Tubes, Cold 807's, and warm room filling AM Sound.
 "I've spent three quarters of my life trying to figure out how to do a $50 job for $.50, the rest I spent trying to come up with the $0.50" - D. Gingery
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« Reply #6 on: April 02, 2012, 08:30:20 PM »

I just changed the rilter in my V2 CDC to a choke input filter. HV I left alone. 6146s like 760 volts.
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Chris P.
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« Reply #7 on: April 02, 2012, 08:42:15 PM »

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.

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ke7trp
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« Reply #8 on: April 03, 2012, 12:21:55 AM »

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.

 

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WA1GFZ
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« Reply #9 on: April 03, 2012, 08:28:24 AM »

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
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Chris P.
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« Reply #10 on: April 08, 2012, 08:32:42 PM »

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.
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Chris P.
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« Reply #11 on: August 26, 2012, 11:36:12 AM »

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?
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w8khk
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« Reply #12 on: August 26, 2012, 01:08:59 PM »

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.
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Rick / W8KHK  ex WB2HKX, WB4GNR
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« Reply #13 on: August 27, 2012, 02:59:20 PM »

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.
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73 de Ed/KB1HYS
Happiness is Hot Tubes, Cold 807's, and warm room filling AM Sound.
 "I've spent three quarters of my life trying to figure out how to do a $50 job for $.50, the rest I spent trying to come up with the $0.50" - D. Gingery
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« Reply #14 on: August 27, 2012, 03:16:21 PM »

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.
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ke7trp
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« Reply #15 on: August 27, 2012, 06:09:38 PM »

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
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Chris P.
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« Reply #16 on: August 27, 2012, 08:44:14 PM »

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.
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ke7trp
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« Reply #17 on: August 27, 2012, 09:27:08 PM »

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
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Chris P.
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« Reply #18 on: August 31, 2012, 02:14:43 PM »

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.
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VE3AJM
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« Reply #19 on: September 03, 2012, 07:23:25 AM »

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
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Chris P.
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« Reply #20 on: September 03, 2012, 02:46:07 PM »

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
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« Reply #21 on: September 03, 2012, 11:27:28 PM »


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
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Chris P.
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« Reply #22 on: September 04, 2012, 10:12:04 AM »

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.
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« Reply #23 on: September 04, 2012, 12:04:50 PM »

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.
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« Reply #24 on: September 04, 2012, 12:26:02 PM »


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

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_-_- bear WB2GCR                   http://www.bearlabs.com
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