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Author Topic: 32V2 tank resonance and sidetone quality  (Read 6361 times)
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WG9P
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« on: October 06, 2012, 10:46:46 AM »

I'm having an unusual problem with my 32V2. The tank circuit requires constant retuning. The fixed caps in the tank have been replaced as they were junk when I got the rig and I replaced the 4D32 final with a new one. Once tuned up, the rig will make 90 watts of power but let it sit for 5 minutes and the output is nearly zero. This is somewhat band specific in that it is more prevalent on 40 meters than any other band. Once it is tuned up it will stay at 90 watts all day long. Very strange. Usually things get worse when they warm up. I will get in there with the freeze spray but would like your input based upon experience.
Like many rigs of this era, it is a beast to work on so I would like to ask for your inputs before I dig into it as I'd like to put it on the bench just once.

One more thing. The cw sidetone audio tone is just terrible on this rig. Any input from other 32V owners? thank you
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KM1H
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« Reply #1 on: October 06, 2012, 11:20:12 AM »

What happens to the grid current?

Did you replace the plate choke bypass as well as the coupling cap? Does the choke look unburnt?

Do you have a scope to watch the drive signal thru all early stages right to the PA grid?

My V2 also had some drift problems but it was primarily due to early stages with weak tubes as well as leaky caps and out of tolerance resistors including in the PTO.

Carl
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WG9P
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« Reply #2 on: October 06, 2012, 11:50:22 AM »

Hi Carl,
Yes, I did replace the plate choke bypass capacitor and the coupling cap. The choke is not burnt and in perfect condition. I do have a scope to watch the drive signals. FYI, the grid drive on the meter looks almost constant before during and after the problem manifests. It varies a bit but as you know you can drive the 4D32 with much less than what the stages can deliver.

 Perhaps it is due to soft tubes in the drive stages but it is such a PITA to take this beast off the desk and onto the bench I am reaching out for a few tips from V2 users.
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N8ETQ
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Mort


« Reply #3 on: October 06, 2012, 12:07:41 PM »


  Hi,

    There are a couple WW Resistors in the rear, below the
VR tubes. Something like 25W jobs for the screen regulator.
Maybe the screen "E" is going away.

   They were both bad in both the 32V2's I've had.

GL

/Dan
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W3RSW
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Rick & "Roosevelt"


« Reply #4 on: October 06, 2012, 07:03:40 PM »

Replace the 4d32 screen bypass cap with one rated at 1kv minimum. The actual capacitance can be anywhere from 500pf to 1000pf.  Do this even if the existing one is not the current time and heat derived thieving component .

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RICK  *W3RSW*
WG9P
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« Reply #5 on: October 06, 2012, 08:30:30 PM »

Thanks Rick. I did just as you suggested as the old 1000pf unit did appear overheated. FYI, all the wirewound resistor look good. Unfortunately i don't have a set of spare driver tubes to sub.  still searching for the culprit.
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WG9P
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« Reply #6 on: October 07, 2012, 01:13:20 AM »

Update: I replaced the 120pf cap in the last multiplier stage as thats the 7mc unique component but no joy. voltages all look good and this problem is isolated to only the 40 meter band selection. Once tuned up on the other bands the rig stays tuned. Only on the 40 meter band does the tank require retuning after being off for a while.
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W3RSW
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Rick & "Roosevelt"


« Reply #7 on: October 07, 2012, 09:00:18 AM »

You originally said that output went to zero as well as detaining. Does output stay up now and it's just 40 that detunes? 

Aren't these things just so much fun? I once had to replace the itty bitty spacers on the dreaded T/R relay. Felt like I was working on a '52 Chevy in Cuba, making my own parts.
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RICK  *W3RSW*
WG9P
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« Reply #8 on: October 07, 2012, 10:42:57 AM »

Yes, on 40 meters when the rig sits idle after tuning up to full power (90 watts) it will go to zero output unless you retune it. On the other bands it drops about 25% after being idle for a while. I am beginning to think the problem may be the capacitors in the tank circuit. After all, the grid current stays strong on all bands including 40.

About 6 months ago I replaced all the fixed caps in the tank with 20KV blue drop caps. Maybe they are from China, I cant tell. I have a brand new one that I am going to put into the tank and see if they are the culprit. Where can I get good USA made capacitors for the tank circuit, preferably with axial leads as there is just no room in that tank for mounting the stuff with 8-32 studs.

I am pretty used to plugging up the nuclear reactor cooling tank with a chocolate bar if you know what I mean. It's all part of the game working on these relics Smiley
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KM1H
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« Reply #9 on: October 07, 2012, 11:02:37 AM »

Quote
About 6 months ago I replaced all the fixed caps in the tank with 20KV blue drop caps. Maybe they are from China, I cant tell.



Hmmmm, you just said the magic word Angry

They can be replaced with 1000V micas if you can find them or even the originals if you kept them, I might have some in the junkbox you can have. At that power level those old style are overkill.

Just looked and Mouser carries the 470 at 1000V in the nice CV-19 package, that handles lots of current and a pair in series is close enough to 220pf so you can do 3 bands with one value.
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WG9P
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« Reply #10 on: October 07, 2012, 11:15:10 AM »

Hard to believe a cap rated at 20KV would crap out that quickly isn't it? I am going to have to put this on hold today as I spent all day yesterday working on it. If it is that cap in the tank then they are all going to have to go. Joy, it's so much fun working in that tight space ha hahaha!
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WG9P
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« Reply #11 on: October 07, 2012, 12:44:09 PM »

I could not keep my hands and mind off this problem. I decided to give the 32V2 one last shot today. Digging around in my jun box I found a 5KV 220pf cap to replace the "NEW" one I installed onto position 4 of the FINAL rotary switch in the tank. It is one of the old square type, 1/4 inch thick and about 1 1/4" rectangular, you know the type.

Not only did it fix the problem of needing to retune the tank all the time the RF output power has jumped up considerably. I checked all bands and in the 700 volt position (the 32V2 has a 600 V and 700 V HV selector switch) I get 140 watts on my wattmeter on 80 meters. I did not know this rig could even make that much power. On 40 I get 110 watts rf output and on 10 meters I get a solid 80 watts in CW mode, slightly higher in phone. I left the rig to cool down with (HV on but unkeyed) and when I came back and hit the key the power was exactly where I left it at 110 watts on 40 meters.

So, what did  we learn?
#1 Cheap caps suck. They may work for a while but not worth the investment as I spent an entire day zeroing in on this problem
#2 Good quality tank capacitors actually work better than the new cheap capacitors as evident in the amount of loss in the cheap ones. even when brand new I dont think I ever got more than 90 watts out of the this rig after installing those cheap blue drops rated at 20KV
#3 As an engineer and technician my gut was that the problem was in the tank circuit but did not want to believe it because of the work I had done there most recently. Go with what you know to be the truth, not what you want it to be!
#4 The cost of buying good parts is nothing compared to the aggravation of doing a job twice

Now, anyone actually own a 32vX that has a sidetone worth listening to? this is my 2nd rig. I recall that my first 32V2 back in the 1970's had a terrible pitch to it as well. Is it just the oscillator design or is it something else? THanks to everyone that contributed to helping me work out this RF problem. 73-Mike

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W3RSW
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Rick & "Roosevelt"


« Reply #12 on: October 07, 2012, 08:23:39 PM »

Great!
Persistence pays.
Makes me want to look at some of my 32V2 caps. I get 90 to 110 out of mine but think it has degraded somewhat in last 15 years.  I am running it and companion 75a2a with a power bucked 115 volt AC line.

My sidetone also sounds like a relaxation Osc. too, rather than a pure sine wave.  Haven't used it much and have pulled that tube anyway.
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RICK  *W3RSW*
KM1H
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« Reply #13 on: October 07, 2012, 09:10:31 PM »

Congrats!

 Any good tech knows not to change something just because its old, injuneers simply cant leave well enough alone. Grin

I came up the old way from Navy tech to injuneer over many decades and still have to remind myself that overanalizing has been the downfall of many Shocked

Repeat after me: "If it aint broke leave it alone" And there are lots of caveats to consider there also....do not even think of firing any BA up with old electrolytics and paper caps for one.

Cant help with the sidetone, never had the rig on CW and if I did my keyer has the tone built in.

Carl
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