Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: martinman on February 12, 2023, 08:33:23 pm
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I just finished a 6v6 plexi build - my first build where I really took my time and assembled things. I read through the schematic and tried to understand as much as I could. When I powered up, I checked all the voltages at the major locations in at ABCDE on the board and all the tube pins via the schematics -- all spot on. Nice!
I put a guitar cable in the input - put my finger over the other end, fire it up, and all I hear is a faint high pitch buzzing coming from the transformer OT when everything is dimed. Nothing, not even a peep out of the speaker.
I'm going to dive in again tomorrow with a fresh set of eyes... Been at this most of the day.
It's the standard classictone 18w OT
Orange, Green, Yellow to their respective taps.
Feedback from board to Green 8Ohm tap.
Switch output to output jack to tip
Black common from OT to output jack (Switch & Ground)
The only thing that I've modified is that I went with only 1 output jack. I'm going to use the other hole for a NFB mod.
Any quick thoughts?
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Hrm… ok, it’s probably not the switch wiring…. Gotta be something else.
I’ll double check the voltages and post tomorrow.
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I put a guitar cable in the input - put my finger over the other end, fire it up, and all I hear is a faint high pitch buzzing coming from the transformer OT when everything is dimed. Nothing, not even a peep out of the speaker.
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I strongly suggest not to do that, as you may be putting the OT under enormous stress and risk wrecking it.
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Any quick thoughts?
Yes, the first time I used an impedance selector I mis-wired it.
Not sayin' that you made this same mistake, but there is something about those switches that is counterintuitive . . . at least for me.
Pictures really help.
PDF is right, but you already knew that . . .
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Here are some pics. They're really difficult to capture, beacuase (like the dummy I am), i wired it before i actually installed it. Live and learn.
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You are using shorting jacks on the speaker output.
NEVER do that. Ditch those jacks and use Switchcraft #11 instead.
Edit: I should have said "Don't use them, if you are going to have more than one output jack". Sorry about that!
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More pics of the build attached.
Voltages:
v1-DC (Expected)(Actual)
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1 - 127 133
3 - .77 .74
6 - 161 166
8 - 1.56 1.56
v2-DC
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1 - 134 131
3 - .84 .89
6 - 238 240
8 - 135 132
V3 - DC
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1 - 185 181
2- 21 21
3 - 33 34
6 - 170 177
8 - 33 34
A 402
B 401
C 278
D 240
E 225
Heaters are 3.3 VAC
All DC voltages seem to be in spec?
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You are using shorting jacks on the speaker output. NEVER do that. Ditch those jacks and use Switchcraft #11 instead.
I always use a #12A shorting jack for the main speaker jack, same as Fender. It's much safer for the OT to operate into a short circuit than it is an open circuit.
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Understood, but he will definitely have problems when he wires that second jack and only plugs in one cable. Maybe he is already aware of that though. Would it be best to use a 12A for the main speaker jack and 11 for the extension speaker jack? I guess he could also just not wire up the shunt on the second jack. Sorry to confuse things...
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Well... Problem solved.. :BangHead: :cussing:
It's the speaker cabinet itself. When I moved it one of the terminals to the speaker came loose. I just. Wow.
I read through RobRobinette's site and one of the first thing is either 1) guitar is not working or 2) speaker / cabinet is not working.
LOL. I went right to the guts of the amp.
This was such a great project - I spent almost 6 months chipping away at it and finally finished it last night in a flurry of activity before the super bowl. In my haste I skipped THE MOST basic test there is!
Lesson learned (again!).
To answer the questions about speaker jacks -- that's good info. For now I'm just going to keep 1 speaker output. With it now working, I'm going to enjoy it for a while and then look for NFB loop mods and use that second chassis hole for either a switch or pot.
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Would it be best to use a 12A for the main speaker jack and 11 for the extension speaker jack?
That's exactly what Fender did.