Valiant load caps question

[w8fax]

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

[WQ9E]

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?

[w8fax]

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

[KC2ZFA]

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

[ke7trp]

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

[N8ETQ]

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

[w8fax]

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??

[w8fax]

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

[N8ETQ]

  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.

[w8fax]

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...

[N8ETQ]

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

[N8ETQ]

  Hoose Ed?

[w8fax]

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??

[ke7trp]

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

[Pete, WA2CWA]

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.

[N8ETQ]

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

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??

[w8fax]

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

[WQ9E]

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.

[w8fax]

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

[WQ9E]

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.

[N8ETQ]

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

73

/Dan

[w8fax]

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

[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

[WQ9E]

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.

[w8fax]

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....