Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jatchley on April 29, 2021, 05:10:42 pm
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So I have Vibrosonic on my bench right now. Early 70s “100w” one. Looks exactly like a MV twin reverb inside. So I was told it has a popping sound. So I thought ok maybe a dirty pot or bad tube. Had a look around first... tightened up safety ground since it was only finger tight. snipped the death cap. Looks to have been recapped with spragues on the board.. and kemets(450v) in the doghouse. I checked all the resistors inside the chassis and all were within a few ohm or dead on with the schematic. and then I fired it up. Heard the popping. Sounded like arcing to me. Turned it off... I take 3 steps away to unplug it from the wall and as I’m reaching for the plug POW a filter cap exploded. The very last 22uf (node D) And since I left the doghouse off it shot back and shattered reverb driver tube (or somehow this tube exploded too) And it sprayed some fluid on my bench that smelled. Sounded like a gun and scared me half to death. What’s crazy to me tho is that it popped while it was draining? My plan is to entirely strip the filter cap board and get a look underneath to make sure it’s not conducting or shorting there... and a friend told me to check the PT CT so I’ll probably remove the entire PT as well and check all primaries and secondary’s. I also plan on rewiring the whole b+line for node D. Prolly just gonna redo the whole power supply and b+ tree. Any advice on more things to check would be great.
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I'd just fix what's broke before doing all that other stuff.
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Oh I forgot to mention. The fuse didn’t blow either.
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Sometimes it just as simple as the cap failed. Not always an exciting story hidden under the board.
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Ope major overlook on my part but the first 2 caps were the wrong value (22uf not 80uf) and wired in series backwards. I saw they were in series and just assumed it was the right way around. Would that blow up a cap further down the line since it’s voltage rating was doubled? I’m just replacing all the filter caps just to make sure if any of the others are damaged.
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Wow Jatchley! That was a real dramatic way to let the smoke out :laugh:
Trust you're safe, no glass shrapnel wounds.
Make sure you use alcohol and clean away ALL that electrolyte from the E-Caps and you might need a little dose of alcohol yourself (Schnapps that is).
Be the truth known, I suspect we all have created our own electrolytic cap explosions when we were younger, but we learnt. (At least I have been a victim of myself, earlier on :l2:)
Kind Regards
Mirek
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the electrolyte is corrosive - pull the board and neutralize it.
--pete