Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ash Telecaster on February 10, 2025, 06:37:13 am
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Hi Everyone!
I finished wiring up my High Power Princeton Reverb.
I used the Hoffman Princeton Reverb turret board in a Weber 6a14hp High Power Princeton. I probably bit off way more than I can chew but it seemed like a good idea at the time.
I strum the guitar, turn on the amp, lights up, hear the guitar, starts quiet, sounds good, quickly increases in volume, then way too much volume, then way way way too much volume, then super loud bassy buzz.....crap, turn it off quick. All this happens in about 10 seconds.
Any thoughts on what the problem might be?
Thanks
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Probably wired up something wrong.
He's a great way to double check your build;
https://el34world.com/Forum/index.php?topic=17701.msg178630#msg178630
And please post a schematic, not layout drawing, and any high res photos of the inside/gut shots of the amp.
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+1 on what Willabe says.
It is helpful if you post a schematic and photos of your build.
It could be as simple as switching the brown and blue wires of your output transformer -- I'm not saying that is what it is, but that is a frequent issue on startup.
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Thank you, I'll upload across several posts.
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Gut shots
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Gut shots
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Gut shots
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I really appreciate you guys taking the time to look at this. Admittedly I am a rank amateur and it shows. However, I have learned so much from this already. I plan on gutting this and doing it again better but I really want to know what I messed up first, if possible.
I don't really care for those cloth wires. There is probably a way to use them neatly but they were a problem for me. Got wax, or whatever, all over the place, would fray at the ends, etc. Are they in any way superior? Or it is just a matter of being period correct?
I tried running the leads up the turret hole and hooking it at the top. This created a weak point at the bottom of the hole and several of the leads broke off. You can see I ran a new lead across the top. I'm going to just wind them around the post next time. Work that will last is more important than pretty.
My soldering ability got so much better as I went a long. I checked each one to make sure the connection was solid but too much solder, sloppy result, etc. I can do better on the next run.
I definitely need a better plan for soldering the tube sockets. I have some ideas on that but I will probably buy a couple just to practice on.
Lastly, it was a mistake trying to do a hybrid design at this stage of my development. There were points that really had me scratching my head. I sketched my moves out before making them but I don't know enough yet to avoid mistakes with any certainty.
And thanks for the link. I'm checking that out now.
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turn on the amp
did you do this step 1st without power tubes so you could verify the bias voltage at the PA tubes??
IF Not, start there, make sure the voltage is at the tube side of the sockets, post reading
IF so and it was good; disconnect the NFB at the speaker n bring back up, better?
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turn on the amp
did you do this step 1st without power tubes so you could verify the bias voltage at the PA tubes??
IF Not, start there, make sure the voltage is at the tube side of the sockets, post reading
IF so and it was good; disconnect the NFB at the speaker n bring back up, better?
It reads -37 on both tubes.
Its probably okay I think you're a genius. It is working now.
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It is working now.
working WITHOUT NFB?? with NFB? or setting bias??
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I didn't touch the bias. I just disconnected the NFB.
Now the amp sounds pretty nice! The tremolo sounds great. The reverb doesn't work.
The amp is loud, it breaks up around 4 though. I wouldn't mind more head room but not unhappy with it either.
I don't notice any noise from a lack of NFB. Using a Tele with single coils. Still want to figure out why the NFB failed. You helped me narrow it down from EVERYTHING to that!
Definitely interested in any other suggestions you have.
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swap the primary leads on the OT (the ones that run to the PA tubes plates)
verify it still works
re-connect the NFB and report.
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swap the primary leads on the OT (the ones that run to the PA tubes plates)
verify it still works
re-connect the NFB and report.
SUCCESS. IT WORKED!
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Can the negative voltage be made more negative. With -37v the 6l6gc might be pretty hot bias.
Is there a way to measure the power tube current, like bias probe or 1 ohm resistors.
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1 ohm resistors.
any builder should install these as a "best practice" (cathode to ground, one "under" each PA tube)
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Not only does it work but it is louder and has more clean headroom!
Muchas Gracias Senior! I am grateful for you help.
Now the effects don't work ...but I can already see something really stupid I did there. So maybe not as hard to fix.
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Tremolo is working. I forgot I had the foot switch plugged in....duh.
Edit: Reverb isn't working. I'm taking it apart and rewiring it. If I plug either lead from the reverb tank to the "output" jack, I can hear the clank when I tap the tank. No instrument signal makes it to the tank.
Thanks again for all your help!
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If I plug either lead from the reverb tank to the "output" jack, I can hear the clank when I tap the tank. No instrument signal makes it to the tank.
That tells you it's the verb tank driver. Your getting signal from the verb return tube.
If I plug either lead from the reverb tank to the "output" jack,
Why are you doing that? Just plug the correct leads to the correct jacks.
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Thanks Willabe,
Why are you doing that? Just plug the correct leads to the correct jacks.
I tried both because I wasn't 100% clear on if it was (output -> input) or (input -> input).
I thought (output -> input) made the most sense but thought I would try both to cover all bases.
That tells you it's the verb tank driver. Your getting signal from the verb return tube.
Thanks, I'm checking that out, appreciate the help!
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I rewired the reverb and now it is working too!!! Woohoo!
Now I just need to figure out the bias. The tremolo seems a little weak and I've read where that can be a bias issue.
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Just wanted to say thanks again to you guys who took the time, especially Shooter!
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I rewired the reverb and now it is working too!!! Woohoo!
Now I just need to figure out the bias. The tremolo seems a little weak and I've read where that can be a bias issue.
There isn't enough wiggle for the 6L6s--this circuit is designed for the 6V6s of the original. You can try replacing the 1M resistor off the plate of the oscillator with a lower value like 470k, but replacing the cathode network with an LED has done the trick for me on 6L6 equipped Princeton type amps.
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Here's trem mods for more trem/deeper trem and slower trem from Sluckey.
Start with #4 the Red LED 1st. Probably enough as stratomaster said.
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Hey thanks!!!!
I will give that a try!
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as long as the solder is flowing, see reply #15