Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: BobL on March 17, 2025, 06:29:46 pm
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Referring to the amp build in this thread:
https://el34world.com/Forum/index.php?topic=31900.0 (https://el34world.com/Forum/index.php?topic=31900.0)
It's a Princeton reverb w/ the reverb and trem deleted. It has been working great 6 months...
I have two of the same 2x12 cabs w/ different speakers, and I wanted to play this amp w/ the speakers in the other cab (P12Q vs GA SC-64s), and it seemed easier to just swap the amps themselves... and now the princeton is making zero noise.
The other amp w/ the other cab works fine. If I plug the speakers in this cab into the other amp, they also work.
I get no transformer hum, no hiss... at one point probing pin 3 on V5 I got a little bit of static, but otherwise... nothing. Fuse is not blown. Tubes warm up...
I think my voltages look ok? So strange.. Any suggestions? Thanks!
B+ Nodes:
A: 454
B: 445
C: 298
D: 233
V1:
1: 156
2: 0
3: 1.2
6: 152
7: 0
8: 1.17
V2:
1: 201
2: 0
3: 1.54
6: 234
7: 21
8: 63
V3:
1: -43.1
3: 447
4: 441
5: -43.1
6: 443
8: 24.4mv
V4:
1: -43.1
3: 447
4: 442
5: -43.1
6: 443
8: 23mv
V5 (rectifier):
2: 455
8: 455
4: 350 AC
6: 350 AC
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Seems like you may have a bad speaker cable or something like that - use your R-meter to check for DC-continuity on each cable wire
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Seems like you may have a bad speaker cable or something like that - use your R-meter to check for DC-continuity on each cable wire
Yeah, I thought of that as well, but I plugged the same cable into the other amp and it made sound without issue.
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Then check all the other connections, jacks etc
(Rule of thumb is if the amp was working fine before you modified anything, and then it wasn't working immediately afterward, it because of something you did)
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If you don't hear any hiss or hum at all with your ear up near the speakers, then it sounds to me like something came loose or is getting grounded somewhere between the power tubes and the speaker jacks. I'd double check all the wiring there.
Also, I'm considering that amp (Princeton AA1164 with reverb and trem deleted) for one of my next builds, and thinking of building it to run properly run 6L6s as well as 6V6s.
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It took me looking at this a couple of times to realize it was operating in reverse of intended. Not sure when/how this got bent, but a quick fix once it dawned on me.
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Then check all the other connections, jacks etc
(Rule of thumb is if the amp was working fine before you modified anything, and then it wasn't working immediately afterward, it because of something you did)
Yeah, definitely knew something happened when I moved it. Narrowing down what I did was where I was a little lost.
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That's one mighty bend. Hard to imagine how that happened.
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That's one mighty bend. Hard to imagine how that happened.
When I was wrestling the chassis into the cab and trying to get the bolts to all line up and get the nuts started all with just two hands, I suppose!