Johnson Valiant Project

Discussion in 'Amateur Radio' started by W6MQI, Nov 22, 2016.

  1. W6MQI

    W6MQI Member

    Here's some pictures of my next project a Johnson Valiant which appears factory built some of the pictures show all the tube sockets pop riveted in place maybe someone can tell me I'm full of it on this assumption. Anyway need to order new caps, and do some cleaning might do some simple mods like the 18k resistor in the VFO, 150v zener in place of the 0A2. Any ideas on how to best to take some of the load off the drive pot would be appreciated.

  2. W5HRO

    W5HRO Administrator

    I had a Valiant back in the early 90's and went through the whole thing and more than once and there are a few key weak links and several things that should be done.

    Weak Links

    1. The 18K VFO Resistor

    2. VHF Parasitic Filter

    3. Modulation Transformer

    4. Caps on accessory socket to gnd

    Mods that should be done

    Leave the 0A2 tube in there and replace the 18K dropping resistor, but mount it underneath the chassis and not inside of the VFO compartment. The VFO tube is in there with the 0A2 anyway so it won’t make any difference, but the resistor should be relocated outside of the VFO compartment..

    Also remove that little VHF parasitic pi-network filter at the base of the plate choke and just use one single HV .001uF cap at the base of it to ground instead.

    Don’t use 866A’s either, use 3B28’s or solid state out those with diodes, but leave all the other tube rectifiers and tube regulators in there.

    As for the audio section that long mic cable going to the back of the chassis is a really stupid thing Johnson did on all of the transmitters. Remove the front panel and the plate switch and install a 3 conductor 1/4" phono jack there instead to where you will have a very short cable going to the 12AX7. That will make the biggest difference in the way the audio will sound when it’s turned up. You can see all of the shielding and filtering they used trying to get the interference out of the audio. That long dried-up cable running from the 12AX7 to the back is a big problem and its acts like an antenna that picks up everything in there. Installing a new mic jack on the front instead is the best option. Then you can just relocate the plate switch on the back where the mic jack was.

    Remove the first stage of the 12AX7's cathode from ground and add a 680-ohm resistor with a 10uF bypass cap across it to ground. Then add a 10uF bypass cap to ground across the other 680-ohm to ground on the second stage. Then add 10uF bypass caps to ground across all of the other cathode resistors to ground on the rest of the stages. I think the last stage already has one, but replace it with a new one. Note: Don’t unground the first stage of the 12AX7 unless you have eliminated that long dried-up mic cable running to the back first otherwise you will start picking up a lot of noise in the audio. Again, that cable is a problem.

    Now, the modulation transformer was always a problem in the Valiant’s so I would add the 3-diode negative peak limiter in there just to be safe, but there really isn’t much else you can do about it other than to maybe also do the shunt modification to take the DC load of it’s secondary, but then you have to increase the voltage on the two modulators tubes a little to compensate and that's a whole other supply modification.

    Anyway, if the modulation transformer craps out it craps out and you just have to replace it. If that did happen one of the old methods was to just stick a bigger modulation transformer in there were the stock one and the two 6146 tubes are then plug 811A’s in the 866A’s sockets and use them to modulate the three 6146’s instead. Then there was also a direct replacement from one of the old Collins military transmitters, but those are probly long gone by now. It was a grey square looking transformer.

    As far as modifying the rest of the audio stages like removing the clipper and little reactor, etc. I don’t recommend doing those since you still have the old stock modulation transformer in there. I would leave those in tack to be safe. You don’t really want to beef it up with the old transformer still in there. The mods I mentioned will be fine though and will greatly improve the overall audio quality and the sound, etc.

    The other problem too are the filters soldered to the pins of the octal accessory socket on the back. They tend to arc during modulation when the caps start to leak. You really don’t need the filters there anyway, but you can leave the coils. Just clip all of the caps there going to ground and remove them. Then move the coils around to make sure none of them are shorting and that there is enough space between all of the connections.

    Other than that yes, all of the electrolytics need to be replaced. There may be a few more items, but those are the main ones that I can remember off the top of my head. I pretty much know that transmitter inside and out.

    Oh, on 40-meters on up the VFO does tend to jump around so when you take it apart you might re-solder all of the component connections. Another thing that would be good is to also DC regulate the VFO tube filament.
  3. W6MQI

    W6MQI Member

    Whats accomplished doing all this?

    Yes there is one funny how Johnson didn't note these as electrolytic caps on the schematic.

    Planning on switching over to 3B28's. A few years back I picked up an unfinished Valiant kit lots of parts missing, but brand new set of tubes never used, plus a pristine cabinet not sure what I'll do with it yet. I now have two sets of 866 tubes one large set, and a smaller version seems a shame to not use them better safe then sorry though. Maybe I can sell them to some audiophile that thinks it neat to watch his tubes glow blue during audio peaks.

    The more I look this Valiant over I'm wondering if it was ever used there's absolutely no indication of excess heat on any parts especially inside the VFO it looks brand new. The 18k Chernobyl resistor was only 2-3% off value with no discoloring. All the wiring is in great shape no baked wires anywhere so it looks to be an easy restoration.

    Read this on W8JI site might give this a try. Some people swear by using diode strings, and others say total BS I still need to learn what this negative peak thing is all about there's so many differing ideas out there hard to know whats right from wrong.

  4. W5HRO

    W5HRO Administrator

    Bypassed stages are better. I said to just add the 680-ohm to ground on the first stage that way it equals the same as the second stage, but it's really best to make both of them around 1.8K to 2.2K max. I was just telling you a way that will keep it simple, because you might want to use that 600-ohm (680) input for something. Anyway, what it does is improve the audio quality. Non bypassed audio stages suck.

    That's the whole point, they were never there, it's a mod.

    I've seen all of that before and only agree with bits and pieces of what he has on his webpages.

    The whole point is the Valiant’s modulation transformer is undersized and most are usually blown or have been replaced when you find them. It's one of the major weak links in the transmitter and Valiant’s like yours that still have the old stock modulation transformer intact are rare. Just add the 3-diode negative peak limiter in there to protect it. You can probably just tap off the LV supply to set its baseline just above ground a little. Just use my improved circuit with the 2 resistors instead of one and it will protect the diodes. Diodes in series will work. You can also add 10K resisters across each diode as well as the main two if you want and it will still work.

    If you really want to protect the transformer more then you would have to do the shunt modification to remove the DC load off of its secondary, but you have do an extensive HV supply modification to get the voltage up on the two 6146's in the modulator. They have to be raised up above the three tubes in the RF final. That's something other hams miss and they wind up with even less modulation than they had before.

    Anyway, I know there's two or three other articles on the web about modifying the Valiant, but none of those hams went through and did the stuff I did to mine and really modified and used it just like others once did.

    The bottom line is the Valiant is a PITA and they made a big mistake using 3 tubes in the RF final. The only way to get the modulation up to 100% and maybe peak a little over on the positive side without changing tubes and etc. is to completely saturate the speech amp to the driver stage. You don't want to do that though with the old stock modulation transformer still in there. The one I had came with the Collins replacement that was pulled from an old military set and I had Peter Dahl build me a new direct Johnson replacement.
  5. W6MQI

    W6MQI Member

    Is this the one your talking about?

  6. W5HRO

    W5HRO Administrator

    No, this is the one below. Also, run the Valiant's plate current at 300mA max and never at 330mA. It will help protect that transformer's secondary. I ran mine right at 300mA which is what most people do. Some even do only 280mA max.


    Anyway, the HV supply usually runs hotter than 600V. I think mine ran around 680V, but I had solid state sticks in there, but if you use 600V @ 300mA you get 2K. If you use the 330mA for the calculation you get 1.8K. So, an RFPA load ohms of 2K is what you want. Either find like two 20W 4K resistors for the limiter or use like two sets of four 5W to 10W 10K resistors in parallel. Then feed its input with enough DC voltage to raise its baseline just above ground so the negative peak won't ever start to turn the three 6146's off during modulation thus protecting the modulation transformer. Should be somewhere around 60V.

    P.S. The resistors can be a little smaller wattage because they are not going to get hot with the baseline only raised just above ground with the Valiant's level of modulation, but I always use bigger ones just so it is more robust. I would make each section handle at least 40W to be safe.
  7. W6MQI

    W6MQI Member

    I emailed Mark Mercer at Hammond about this transformer it's available through Digikey 4 week lead time. Did a search on Digikey web site nothing came up so I emailed Steve.Dahl@digikey to find out if I need to order direct through him or not. Steve was a contact Mark gave me at Digikey.

    EFJ P/N 22.1285, SNC P/N P2998
    PR) 840 VCT @ 0.212A CCS (7300 OHMS P-P)
    S1) 450 VCT @ 0.300A CCS (2100 OHMS RF PA)

    DM) HT = 3.750 WT = 3.125 DT = 3.625 MD = 2.500 MW = 2.500
    PRICE) $190.00 Plus S&H FOB Buffalo, NY WEIGHT) 5 LBS
  8. W5HRO

    W5HRO Administrator

    Hopefully that is right, but it's not the same one he built for me back around 1990/91. The Valiant's Modulation transformer has two secondary windings, not one. The one he built for me had S1 and S2. It looks like someone on down the road after me converted it to one winding with the center tap. If those are AC voltages then it is correct. If they are DC it is wrong and they misunderstood the specs.

    In the transmitter the transformer had both of the secondary windings connected in series, but still. Again, hopefully they didn't make a mistake when they converted it to a single secondary because if they did it won't work. Most of Peters specs used AC voltages and currents which was the correct way and it always threw some hams off because they thought they were DC. Then he started using a mixture of both AC and DC in the specs because of it.
  9. W6MQI

    W6MQI Member

    A while back ER was selling some modulation transformers for one of the Johnson rigs I guess it was a one time group purchase, but I can't find any ER magazines around here to look.
  10. W6MQI

    W6MQI Member

    I just looked at the transformer in the radio and yes there are 7 wires not 6 like their spec sheet shows sounds like another email is needed. I would assume the voltage is RMS I always thought all transformers were spec at RMS, but what do I know. The Valiant schematic only shows 6 wires 3 pri, 3 sec what's with that? Does the center tap on the sec side have two wires S1, S2?
  11. W5HRO

    W5HRO Administrator

    The secondary has 4 wires (two windings) but in the transmitter they were connected in series so it acted as one winding with a center tap. The new Peter Dahl being sold by Hammond may be correct. If so they just modified the original design and made the secondary one winding. The original Peter Dahl though had the 4 wires like the original stock Johnson transformer.
  12. W5HRO

    W5HRO Administrator

  13. W6MQI

    W6MQI Member

    Bag of capacitors came yesterday and the 3B28's are on their way. Did some posting on some other sites to find out about that Hammond modulation xmfr nobody really new anything about it. What's funny is I emailed Hammond again to get more info and they were sort of clueless on the wiring of the new xmfr vs the old design so that though up a red flag for me. I did find this guy for $155.00 he will rewire my xmfr with the correct wiring, better insulation on the wire along with insulation paper he also apparently does a better job of dip and baking than the factory did. Now do I pull my good stock xmfr out and send it for rewiring for piece of mind or roll the dice with the stock xmfr?
  14. W6MQI

    W6MQI Member

    Are those copper enamel coils L31-L36 really needed? I've got two right in my way where I would like to install a fuse holder. Seems like I remember reading somewhere those coils are pretty much useless.
  15. W5HRO

    W5HRO Administrator

    You mean the ones that connect to the primaries of the two main transformers with the .005uF caps between them to ground? You can remove those, but replace the .005uF caps to ground with some better surge protection caps instead. That's what I did with mine years ago. Just eliminate the coils and use better surge caps instead.

    Just don't forget to cut those bypass caps to ground loose at that accessory socket. Those lines connect to the modulator’s output and those caps leak and also restrict the highs when you modulate. That socket was for using the Valiant to modulate an external amp like in the Desk KW and those filters were always a problem.

    P.S. Radio Shack use to sell a pair of AC line surge caps in a package years ago and they were cheap and worked great. That's one of the downsides of the Shack's demise. A few of those key reliable easy to get items we took for granted are now gone forever.
  16. W6MQI

    W6MQI Member

    I was planning on using Y2 caps in place of the .005 caps that are there now on the primary lines.

    Was planning on doing this.

    Just got done testing all the meter shunts for meter accuracy used a power supply and various resistor values depending on which shunt I was checking. I was surprised to see all the meter positions were almost on the money might still change out those wire shunts to a more modern low resistance resistor though.

    I don't think this Valiant was ever used or very little anyway everything inside seems to be in really great shape almost new like.
  17. W5HRO

    W5HRO Administrator

    Hey, I searched around because I also wanted to remind you about the VHF parasitic filter I mentioned. You may or may not have already seen this, but below is what you also need to eliminate. The bottom line is you only need a single .001uF cap to ground at the base of the plate choke. The only thing that little pi-network filter does is restrict the audio response when you modulate and in time it will burn up like in the pic below. The other thing about the Valiant is that it puts out bad spurs in the 200Mc range no matter what you do and there is no way to stop it. I forget the exact frequencies in which it happens, but it’s somewhere around 200Mc on up. It has something to do with the 3 tubes in the RF final and their impedance and the capacitive coupling from the 5763 RF driver stage.

  18. W6MQI

    W6MQI Member

    I just left one of the original .01 caps in place , and now that I think about it I believe I forgot to attach the bottom of plate choke L11 to R16.
  19. NewWave

    NewWave Member

    For me it looks strange of course, but looking really nice at the same time.
    All parts are still clean after so many years..

    At home i use sometimes an old Kenwood TS 140S Who's working stable again after replacement
    the Eprom socket on the exciter board.
  20. W6MQI

    W6MQI Member

    After reading about your transmitters I feel a little impotent with my little pip squeak Valiant what I lack in size I make up in quantity though.
  21. NewWave

    NewWave Member

    More Power is not always the right way, but sometimes it's helpful during conditions or so.
    But a small transmitter like yours is easy to put it quickly on air on almost all places.
    I have to carry a 100 KG power supply first... :icon_crazy:
    And believe me, that you have a greater range during conditions as you might think, even with low power.:surprised:

    In Holland we have some people who use ONE (1) Watt only and receive (audio) emails from almost whole Europe.. Good Modulation and a the right antenna is more important as a strong carrier !!
  22. W5HRO

    W5HRO Administrator

    I would just replace that one .01uF with a 2kV to 4kV ,001uF cap. When you modulate that .01uF 1.5kV cap will restrict the audio response a little, but a .01uF is the max you would even want there. A .001uF will just work better and if that's one of the original .01uF 1.5kV caps that was in there then it's probably already leaking. A 600V transmitter with 100% modulation is 1200V and the Valiants ran hotter than 600V anyway. Those 1500V caps were too small and borderlined from the very beginning.

    P.S. Do you have a spectrum analyzer or a modern 220Mc transceiver (1.25-meters)? My ham neighbor down the street back in Tulsa use to listen to me on his 220 rig on SSB (no AM mode) when I was on the Valiant because the spurs were so high :icon_angel: Back in 1950's Johnson probably never even knew the Valiants were doing that and there wouldn't have been anyway to stop it even if they did know other than to redesign the whole PA section.
  23. W6MQI

    W6MQI Member

    Well I'm screwed went to power up the Valiant today and nada, nothing, zip turns out the power switch is porked CRAP!!! in order to replace the switch the front panel needs to come off think I would rather have a tooth pulled instead.:twisted: Last time I pulled a panel on a Ranger the very thin bakelite VFO coupler broke that made my day. Also need to find a tool to remove those knurled nuts on the switches pliers just don't cut it, they always slip followed by loud cursing from either scratching to panel or pinching my finger in the pliers jaw. Anyway that's the latest getting ready to make a large purchase from Mouser for ART-13 power supply parts I may switch over to the ART-13 for awhile, and put the Valiant on the back burner.
  24. W5HRO

    W5HRO Administrator

    Put a 1/4" 3-conductor mic jack on the front where the plate switch is anyway like I suggested since the front panel must come off. Actually, the panel on the Valiants are not that difficult to take off. It’s one of the easier one of the Johnson's to do.

    Also, get an orange bottle of that Nu Finish liquid car polish and polish up the panel before putting it back on. Two coats works best. You will be surprised at how well it will look after doing that. It doesn't have any abrasives in it that will rub the silkscreen off.

  25. W6MQI

    W6MQI Member