Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: okguitarman on November 21, 2016, 10:24:28 pm
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keep in mind I have only built a few amps. I was asked to look at this amp I was told he got it from Mojo. and was his first build.
When he tested it tubes light but no sound (none).
1. Ok, I opened it up first thing I found board is not mounted and the 2 ohm tap on output sec. was tied to ground.
2. Checking output jack joints and tip wire fell off. I thought there it is. Still no sound
3. Plastic key in base of power tube was gone said he broke it, thinks it is still good.
4. pots are all loose,tightened them up.
Would that kill output transformer 2ohm tap tied to ground.?
I swapped stage1 & tube 6 PI still no sound
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Could be a lotta, lotta things.
When you repair amps, if you take in a broken amp, there is a virtually certain possibility that it worked at one time. Those of us who have worked on amps, we have seen many Super Reverbs or Twin Reverbs or Deluxe Reverbs, all of which have many many things in common.
I used to work at a factory where electronic stuff was made. Sometimes 47 consecutive units came off the assembly line and failed initial testing. And sometimes, Consuela put that same diode in backwards 47 times. After 3 or 4, I didn't even have to look, I knew D22 was backwards. Those took 30 seconds to fix.
When you are trying to repair a kit, per your story, it NEVER worked. The difference is that you (the repairperson) have to check literally everything. Were wires soldered to the right places? Are jumpers in place? Are wires stuck through tube socket lugs or pot lugs too far and are now shorts? Are there bad solder joints? If now you throw in rotated power tubes with broken base keys, that can certainly blow stuff up and blow stuff up in ways not ordinarily encountered.
That doesn't mean it would be hard to fix it; but we who have done this can recognize certain things very fast and these things are generally not at all "hard" to deal with. But those things we recognize are for the most part 2-3-5-8 things that happen commonly in these amps that cover 95+% of all Fender faults.
I realize I'm not helping you much, but there's no great answer. It could be a hundred things, or several of a hundred things.
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Your absolutely correct. LOL dang me going to be a long night!
would the 2 ohm tap being grounded cause the output to fell? I've never seen that.
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SPEAKING of jumpers, there do not appear to be the normal "over the board" jumpers on your gut shot. Those distribute power to the entire amp and would stop it from making a peep if they weren't there. Go look in Doug's schematic library for "Super Reverb AB763 >>LAYOUT<<.
Print it out.
On that parts board, which is upside down relative to how you photographed yours, you will see generally along the top side of the parts board wires going to boxes labeled "Z", "X", "Y", and "D". Well, "Z" has to go to "Z" and "Y" to "Y" and "X" to "X" and "D" to "D".
Those wires (called jumpers) don't appear to be present on your amp and the amp will absolutely not work without ALL of them.
The 2 ohm tap being grounded frankly is NOT likely to have caused damage to the OT unless the owner left the thing on for hours and hours without it working. Normally, Fender amps DO ground the output lead if there is no speaker plug inserted into the jack. Not saying it does the amp any good but it won't blow it up, again, unless it was left on for a pretty long time. Even then, probably not.
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Ok Thank you.
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1. Ok, I opened it up first thing I found board is not mounted and the 2 ohm tap on output sec. was tied to ground.
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Would that kill output transformer 2ohm tap tied to ground.?
No. The stock Fender setup for the main speaker jack is to short the tap to ground when no speaker is plugged in. The transformer survives just fine.
At this point, assume no sound = wrong wiring, especially given the things you've found so far.