The AM Forum

Hello all. I appreciate the help/comments on my VFO problems that I am having on my othet Valiant. This question is on another viking valiant that I have picked up. I replaced the power supply caps right out of the gate, but I still brought it up on a variac. Everything looked spiffy until I flipped the transmit switch. One of the 866 sockets ( changed these to 3B's) sockets fired off to ground. Replaced that. Then had a voltage burn accross a terminal strip that the 866 cap leads came off of. Replaced that and the cap leads also with hi-voltage wiring. This rig is factory wired, but it has had a little tinkering done. Some caps replaced and someone put a 3 wire cord on it, but no fuse. I am using the variac and it is fused, but I will change that. Anyway, after all that rambling, here is the problem. I have drive on all bands, plenty. I can hear the vfo in a receiver, no problem. The meter shows about 275 mils of plate current, but only about 5 watts out, and I cannot dip or load the finals at all, on any band. (btw the low voltage regulators fire on switching to AM). I cannot see any burned areas on switches or obvious cooked parts, but if the mica caps or the "special" cap is cooked, will that stop the rig from loading up???? Thanks for any help....Al/W8FAX

Al,

It could be the fixed loading caps although I have never seen them all go out at once so normally you will see differing levels of plate current (and malfunction) when the coarse loading is set to different ranges.  Ditto the additional caps used for some of the lower bands for the plate tune control.

Try tuning up on 10 meters but be careful because if the neutralization isn't set properly this will get flaky.  Normally on 10 meters the coarse loading is set to 10 and this takes the fixed loading caps out of the picture and on 10 the additional fixed caps in parallel with the tune cap are also removed.  If it still is showing the same 275 mil plate current with no dip then the fixed caps aren't the problem (or at least aren't the only problem).

Does the plate current not vary significantly with grid drive?  Have the filter caps in the bias supply been replaced?

Hi..I appreciate your help. Yes...the plate is current is about the same on 10 meters and there is only a very slight dip when moving the final cap. The plate current will vary all the way down to zero if the drive pot is moved. Plenty of drive (on the meter) And also, all power supply caps have been changed out....AL/W8FAX

it's behaving like there's zero loading capacitance.

Make sure that the mechanical selector under the chassis is in the right position.  The block can slip on the shaft and then, it wont tune up.

The loading section on the valiant is complete junk.  It will be a constant source of trouble if you change bands often.  If there is trouble the contacts then get damaged very easy and arc.  I suggest you take an old tooth brush and contact cleaner  or deoxit and scrub the wafers at the "rivits" to make sure there are no carbon tracks. Tenson all the contacts also.  Then replace the special loading cap with small doorknobs. One side right to the chassis, The other with wire up to the loading switch. problem solved forever.

C

Hey Al,

   Put an ohm meter from the center pin of the output
SO-239 to the "Tank Side" of the Plate Blocking cap.
Should read close to "Zero" in all settings.That rear
section of the "Band" switch is "Toastable"

73 & GL

/Dan

OK. I have taken my deoxit pencil and reall worked over the band switches. I can see no traces of arcing with my "super eyeball" mag glasses. I have plenty of grid drive on all bands. I am able to get about 50 watts on 20 and 15, but way less on the other bands. I swapped out the plate choke, bypass doorknob and the small ceramic bypass caps on the bottom of the choke. I swapped with a Valiant that is known to work. The plate current never reaches more than about 300 mils, if that. I also noticed that the modulator at rest current is zero, but that is another problem. Duhhhh.........10 cents a pound??

Ed..I tried the ohm reading and it is zero on all bands....AL/W8FAX

  Hey Al,


         Man, that Sux.

  If you have one of them "High Falutin" DMM's
with a freq counter/"C" readings here is what
you should expect.  The mention of "Residual"
is the amount of "Pf" my meter reads tweens
the leads.

Are you reading these at the same place?? (coax center to tank)?? I have a cap meter, but I am seeing no change at this measurement point, other than my leads jumping some...

Insert Quote
Are you reading these at the same place?? (coax center to tank)?"

  Well loading caps are in "Parallel" with ant. jack. I measure
coax center to chassis..

/Dan

  Hoose Ed?

Yeah...long day. Any way with my spiffy cap meter, I am not getting anywhere near your readings. In some cases moving the switch has no change in readings. Changing bands effects it too, but not much. .  I do see a swing with moving the fine coupling cap so at least I know that is working. At least its hooked up lol. The "rotary" block is locking in tight when I move it by hand and seems to be doing what is supposed to do. Is it possible that the "special cap" is cooked??

Before going further can you set the Clamper tube adjust and try again?  Its a simple procedure in the manual.

In the SSB mode you should have the resting current on the meter.

Next. Key up and measure the Screen voltage at the finals.  If its off, then the power will be low and you wont ever be able to load it up.  I think its supposed to be 125 to 150 but check the manual.

After this,  Pull two finals and try to load each one at a time.  Each one should do 125 MA like a Ranger. Set Grid drive at 2.5 MA for a single tube...   Measure power output. Should be 60 watts each or so.  If you have bad finals, You can find them this way.  Make sure the unused plate caps are not going to hit anything...

I am kind of thinking that something else is going on here..

C

As was indicated , check the clamp tube, it's adjustment, and also check the screen voltages. Check all the tube socket voltages, chart on page 31; page 32 has resistance measurement chart.

Hey Al,

    That "Goofy" Cap has 3 sections, 1200pf 900pf and
600pf. There is another fixed 300pf in there and the
variable is also 300 pf. Set the variable to full mesh
and read the pF's at the output jack. You can almost
calculate which cap(s) are bad. Don't even have to
pull that Heavy Motha' out of the case.

    A check of the Screen Voltage to the PA is also
easy to do. A check of the PA bias is also easy to
do. Some Valiant 's had 2 pots on the right side of the
chassis. one for MOD Bias and 1 for PA bias. Since
you do have drive you could just "Pull" the 6AQ5
Clamp tube as a quick test.  The "Bias Supply"
can also be problematic.

73

/Dan

OK...so far...checked resistance per manual. All pretty close except one. Bad resistor solder or57, which is in series with the bias set pot R62. Was not able to set bias to -52 volts per manual, only sometimes. After re welding, bias could be set and would stay there.
Pulled clamp tube and plate pinned as expected. Readjusted that per manual. Kinda touchy and just have to find the "spot" so it doesnt take off on any band.
Also replaced buffer tube 6cl6 which appeared to be gassy. I thought I had replaced this earlier. Maybe not, or a bum tube.
Installed fuse and new line cord.
Replaced clamper tube 6al5 with new tube....just because. Re adjusted clamp pot.
All the finals checked OK.
Can now load to about 140/ 150 watts. Loading is still a little hinky and course loading not working the same as on my other Valiant. I still suspect that special cap. A word about that. Early on I could not get anything to load. I loosened the screw that holds it together and re tightened. Not sure why (loose/bad connection) but the cap readings were now changing with the coarse loading switch measured at the ant connector. Was not able to get that before.
I still think it is not loading exactly correctly, but at least its making some watts.
Moved to mod section. The pot on the side,r61, had been doped up with some magical crap to keep it from turning. Finally got it loose and was able to set the resting current on the modulator. Replaced all the tubes in mod section including 6146's with known good tubes. However, audio sounds like crap and now I noticed some arcing on one of the bakelite strips where the HV goes to the mod 6146's. This is the third tie strip I have found that has arced.
Question...what voltage rating do you fellers use when you replace the layered mica cap?? I am gonna do that sooner or later.
Anyway, onward. Thanks for a ll the help so far. Still aint done, but gonna ease off a couple of days....AL/W8FAX

Al,

Instead of following the manual instructions I find it easier to set the control so it does not provide clamping action, load the final to normal rated input (on CW) with normal drive, and then adjust the clamp control to the point just shy of where it causes a drop in plate current.  This provides proper clamp action without reducing input.

It is unusual to find so many arcing strips.  Does it look like someone has been in there spraying cleaner/lubricant or some household cleaner?  Many household cleaners leave a conductive residue when they dry and if there is evidence of this you may need to go back in with a proper cleaner.  I have had to use electrical motor commutator cleaner on a couple of radios to remove the residue from previous owners' cleanup attempts.  It does a good job of cutting through grease and grime and evaporates without leaving a conductive residue but keep it away from dials, decals, and other such cosmetic items.  If sprayed around shaft bearings you will need to add a couple of drops of synthetic oil when finished.

Improper cleaners can easily cause corrosion around ground connections and it would be worthwhile to loosen and then properly tighten all such connections in the final area.

I cant tell. Someone before me changed the main supply caps and a couple of others. I did the rest. One of the strips that arced had been soldered on. But the other two did not appear to have been disturbed. It does seem kinda strange. The underside IS really clean compared to the rest of the rig...who knows. I dont understand how a rig could have so many problems at once. I can see the load caps, or power supply, or modulator, etc etc, but I dont see how all could go at once??
Does anyone know if the pots on the side for setting bias and mod current is a newer modification that Johnson did, or were the older rigs the ones with pots?? Thanks...Al/W8FAX

Al,

The bias network change was a running change for later production and it was published as a service note for owners who wanted to make the change.  It was a required change if you planned to use the Johnson 6N2 transmitter with the Valiant (the Valiant supplied all operating voltages)  in order that the Valiant modulator bias would be independent of the final drive level.

Either version works fine but the dual pot version is far easier to adjust.

 Glad to hear your making good progress Al!
I don't know anyone who has just 1 Valiant.

73

/Dan

I have two. One was built from a kit and the other is factory wired. I like these old rigs but dont understand their operation very well as far as technical. I am learning tho' for sure. AND I appreciate all the help. Saves on hair pulling (relevant to quantity) and just giving up. My other Valiant was running great, but has developed a severe VFO problem. One at a time...lol....AL/W8FAX

OK. Now have about 150 watts out on 40 meters and more on bands below that. CW mode. I believe I have got all the arcing and sparking problems fixed until the next fire. Audio...I have checked the ohm as per manual and seem to be in the ball park on the tubes. The ohms check per the manual I have not got yet, as the wires are old and only one or two resemble the colors in the manual. The mod transformer is wired a little different than my other rig. This one also has the pots on the side, and my other one does not. However, the audio on this rig sounds very raspy and unclear. I also have to run the audio control up pretty hi to get the meter to start kicking. I changed out the audio section tubes with known good tubes and swapped the 6146's also. I am going to hook up the scope shortly and peek at it. Ant suggestions before I start digging??? Thanks...Al/W8FAX

Did you replace the cathode bypass caps in the audio section?  If those are open or down on capacity that will reduce audio gain dramatically.

No..I did not...not yet. I just had it on the scope and it is hard to explain the wave form. NOT sinusoidal, and I cannot get modulation up to get "beads???" on the wave form either. Meter swings plenty but....here we go again....

Replace the 10uf bypass cap on the audio driver and see if that helps.

OK..I replaced the cathode cap (10 mfd). Had to go get one from the trusty surplus store. It made no change at all. I guess next is to look at voltages on the tubes and transformer? Ohms check out seemed to be OK, some up a little and some down a little. I get modulation but have to have mod control up pretty hi and the audio is very "raspy" for a word. The scope is a weird shape also and as best I can tell only reaches about 50% modulation or so. Increasing the audio swings the mod current way too high, as expected, but does not help the raspyness. Is it possible that the driver or mod transformer is defective?? It seems if one or the other was open or shorted that I would see it on the meter or scope, but dont know myself....also rechecked the bias on the modulator...OK. Swapped tubes again, including the rectifiers in the low voltage section, as these are the only tubes left that have not been replaced. Also tried another set of 6146's in the mod, but no change there either. Al/W8FAX

Check to make sure the clipper control isn't the problem, that raspy sound would happen if the clipper circuit is operating at full clipping.

Using your scope trace through the audio section and see where the problem starts.

Don't forget that the metering resistor (particularly in a kit built Valiant) could be way off so measure the actual cathode current of the modulator tubes with your DMM.

Alright...the score so far. I injected a 1000 hz sig at the mike input and started the checking with my scope. I found one cap that had sig on one side, but weird on the otherside, but still passing, just reshaping somehow??? Cap # C83. I was getting a nice sig out of the 12AX7, but further down the line it went to crap. After I changed that little cap it cleaned up. However, the sig coming out of the mod xfrmr was not good either. What I found was that it would be good at first when turning on B+, but would soon go to crap. The 22 ohm resistor in one of the 6146 mod tubes was heating up and changing value rapidly. I just caught this by chance because when it was cool it checked OK. When I replaced the HV wire to the caps (due to arcing underneath on a term strip) I had pushed some heat shrink over it. It got hot enuff to shrink the shrink. I did not have another 22 ohm resistor, but I did have a 32. I put it in there and guess what. The mod sig output on the scope cleaned right up. Applying voice looked good also. I got a quick check from W9T on 80meters and he said it sounded good. The audio input knob still seems a little high to me, but that is only compared to the other valiant I have. I hope that this should at least get things under control for this rig. I still have to open the VFO and see if the meltdown resistor has been changed. Also...the keying waveform looks good, and the leading edge is not real sharp. I also think I will start a search for door knobs to replace the layered mica in there. I really want to thank everyone who pitched in help and comments on this project. When I first brought it up and saw all the arcing and sparking I never thought it would ever work...but it does. Plus I learned some stuff too......Al/W8FAX

One other comment...the cathode cap that was suggested to get changed may have been bad, but changing it showed no change since the problem(s) were elsewhere...prolly a sum total thing??...lol...Al/W8FAX

Well, I have been on the air now quite a bit, and so far so good. Good audio reports and no drifting or chirping on CW, no arcs and sparks or smoke. I rcvd and appreciate the audio recording from Jim, KJ9T. I felt it was pretty much done until I can round up some caps to replace the band caps and layered mica cap, so I put it back in it's cabinet. A sure sign of optimism because that is not fun either. Thanks for the help everyone, now on to the next Valiant that I have.
One question....I have seen pros and cons about this, but what is the consensus these days of removing all the little coils that were meant to be TVI traps I think, and just wire up straight??? I do not see much use for them now. Thanks again....Al/W8FAX

Al,

  Unless you are a purist I would remove them. There are several reasons why this is a good idea.

1. They are not needed in today's RF environment.
2. It is questionable that they even did what they were intended to do.
3. Other rigs of the era, like Collins, used simple capacitive filtering.
4. There have been stories of the open enameled wire chokes shorting and causing damage.
5. Johnson went way overboard putting these LC filters on pilot lights, even the lights that
went through the long tube to the jewel on the front panel. 

See the September 2011 ER page 28 Ranger article for an analysis of this and a better replacement should you decide to not completely eliminate them. I used the ferrite LC suggested there on the AC line, Mic PTT, and CW key lines as well as the meter leads in my Ranger. All others I completely eliminated. Even that was probably overkill.

The recommended replacement is an Amidon FB-776301 with 2 turns of Teflon and a .1 cap.  I used more turns  (like 6-8) and a smaller cap except on the AC line.

Doug