Smoke get in your eyes

[KB2WIG]

A most curious crap out.
 The Platters would understand, but I'm quandering. In my experience, when the smoke comes out, a 'lectronic part is smoked. Well, this Viking 2 is letting out a wee bit 'o smoke, but keeps on modulating. I can't find a schorched or burnt or even a suspicious looking part. By the time I finish with the Jesus stick, the only parts that are warm are the tubes. If I keep the mic controll around 2, and don't speak too loud, no smoke comes out.

The wisps seem to hang about the mod tubes. Wierd. Oh well, it was nice fer a few days.

klc

[Steve - K4HX]

Keep running it. It will make itself obvious eventually.

[K1JJ]

Is there a potentiometer in the vicinity?  They can let out smoke but the insides stay hidden... up to a point.

No luck?  Next, take the rig out of the case and fire it  up.  Put it on its side with a mirror behind it.  Put the lights off - dark room.  Key and talk and it will show itself like a ghoul in the night.

T

[K4RT]

If you have a digital camera that can shoot video you might set it on the bench so it captures the mod section and maybe it will catch where the smoke is coming from.

I will soon be using my digital camera for such a purpose.  A couple weeks back I fired up my Apache and heard a pop and saw a flash in the speech/modulator section underneath the modulator tubes, but I was not positioned to see what flashed & popped. Using a small dental mirror and flashlight I'm unable to see any visible evidence of a damaged component in that section and all components are relatively near spec, except an open .2 ohm 1 watt precision resistor between pin 2 of both mod tubes and HV power supply. I don't see any visible damage to that resistor's exterior. I know a capacitor can pop when it fails but I've never heard of a failing resistor doing that.  A misplaced VFO enclosure screw was nestled in some nearby wires near a terminal strip, so maybe that screw shorted something. On Friday, all tubes were removed and all tested good.

The screw has been put back into the VFO enclosure and I'll replace the .2 ohm resistor and try again, but this time with the camera set up to -hopefully- capture what happens.

73,
Brad

[KL7OF]

Run it in the dark

[KB2WIG]

I'm running in the dark......


She's been on her side, normal side up, and up side down. I've tried the romantic mood lighting. Brad,the video cam, that's a great idea. If only I could find my cheep camera tripod

Yes Steve, That I know fer sure. I think I'll get on 3875 and maybee do an atomic yeah-a-low.

Tom, there's a  pot for the klamp tube right near the mod tubes... maybee here.


klc

[KB2WIG]

The plate cap/conductor on one of the mod tubes is smokin. And inside, there were parts of a 22 ohm resistor.


klc

[Opcom]

"were" being the operative! hard to blow that but maybe it all started with a bad connection!

Got pics?

[W3RSW]

Ooh, the dreaded parasitic suppressor?  Apparently the 22ohm was doing its work. Hopefully a replacement won't blow again. Makes you happy when you find these zorches.

[WQ9E]

Sometimes those resistors just drift up in value and as the heat builds the problem is exacerbated until they finally reach the smoke point, your experience with it happening during longer transmissions with higher modulation level points to this cause.  I had to replace the resistors in one of the V2 transmitters that came across my bench.

I would replace both of these resistors AND check both tubes just to make sure that both are equally healthy.  If your tube checker doesn't handle this variety try them one at a time in the transmitter just to make sure they are drawing equal idle current.

[KB2WIG]

"  Got pics? "

Yes, I do. Now I just have to find the appropriate cable to load them on the computor.

"Ooh, the dreaded parasitic suppressor?'

Ahhh Yes, the supressor. Not 'suppressors' but supressor. There was only one, and that one was hidden by a insulating sleeve at the plate cap. The other plate cap didn't have anything attacked, other than the lead. When I soldered in the new resistors, I noticed that the  plate cap had the "plug like" end of a resistor attached. Evidently, the resistor craped out, and rather than spending the $0.04 to replace it, the op soldered the lead directly to the plate cap. Nice work if you can get it (and you can get it if u want).


"drift up in value"  Yes they do.
 
"...try them one at a time in the transmitter just to make sure they are drawing equal idle current. "   Yes, I will.  Not having a tube checker, I'll use the pull method.  

It is interesting that the coil/resistor suppressors on the 6146s' are mounted about 3/4 inch away from the tube. Some of this may be attributed to the fact its higer voltage and also RF. But the mod supressors are hidden inside the insulating 'boot'. I had no idea that they were there. I didn't even know that they were missing.

I'll post a few pics for future generations.

Thanks guys.

klc

[WQ9E]

The early Viking II (and all of the Viking 1 ) transmitters did not have these resistors.  They were added as part of "Mod B" issued by the factory and the entire modification improved the low frequency audio response and negated the need to observe modulator plate cap phasing to avoid oscillation.

You can find this document on edebris in the Viking 1 directory:  http://bama.edebris.com/manuals/johnson/viking1/mods

[flintstone mop]

play some AC/DC music on 3885 and that will let more smoke out.

[KB2WIG]

" play some AC/DC music ..."


Actually, I'd like to try Ravel's Boléro. That baby would light up the 807s.


klc