Princeton reverb bad distortion

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JoshBernstein
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Princeton reverb bad distortion

Post by JoshBernstein »

Hi everyone,
A while back i built a princeton reverb off a mojo fiberboard. The clean is gorgeous, but the drive is absolutely horrendous. When its on the edge of breakup theres just a small amount of really sweet sounding overdrive, but as i turn the amp up it just gets buzzy and blatty and disgusting. Rolling off the treble and bass controls doesnt seem to effect it very much. Ive tried it through a couple different cabs and it occurs with all of them.

Im using a heyboer power tranny salvaged from an old champ build, classictone output tranny, heyboer reverb tranny, amperex bugle boy in v1, sylvania 12au7 in v2, rca 12ax7 for v3 and v4. Power valves and rectifier are new production jj. Reverb tank is a belton 3 spring tank. Speaker is a 10" jupiter ceramic.

Here are some pics and a voltage chart
Thanks!
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Last edited by JoshBernstein on Thu Jul 13, 2017 2:41 am, edited 1 time in total.
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JoshBernstein
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Re: Princeton reverb bad distortion

Post by JoshBernstein »

Voltage chart
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frankdrebin
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Re: Princeton reverb bad distortion

Post by frankdrebin »

286v on pin 4 sounds pretty wrong to me, I'd check out what's going on between that and the rectifier output.

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sluckey
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Re: Princeton reverb bad distortion

Post by sluckey »

V5 and V6 pin 4 voltage is way too low. Should be almost the same as pin 3. You have used a 15K resistor where a 1K resistor should be used for B+ screen node. Put a 1K on the board and see if that doesn't improve things. See pic...
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Stevem
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Re: Princeton reverb bad distortion

Post by Stevem »

A 12ax7 used for the PI will drive the shit out of the outputs way too early!
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JoshBernstein
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Re: Princeton reverb bad distortion

Post by JoshBernstein »

sluckey wrote: Thu Jul 13, 2017 7:18 am V5 and V6 pin 4 voltage is way too low. Should be almost the same as pin 3. You have used a 15K resistor where a 1K resistor should be used for B+ screen node. Put a 1K on the board and see if that doesn't improve things. See pic...
Okay, definitely will swap that out, i cant believe i missed it!
Stevem wrote: Thu Jul 13, 2017 10:49 am A 12ax7 used for the PI will drive the shit out of the outputs way too early!
What would you reccomend for the pi in that case? I have a few phillips 12at7's laying around if that would be better.

Thanks!
-Josh
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JoshBernstein
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Re: Princeton reverb bad distortion

Post by JoshBernstein »

sluckey wrote: Thu Jul 13, 2017 7:18 am V5 and V6 pin 4 voltage is way too low. Should be almost the same as pin 3. You have used a 15K resistor where a 1K resistor should be used for B+ screen node. Put a 1K on the board and see if that doesn't improve things. See pic...
Okay, definitely will swap that out, i cant believe i missed it!
Stevem wrote: Thu Jul 13, 2017 10:49 am A 12ax7 used for the PI will drive the shit out of the outputs way too early!
What would you reccomend for the pi in that case? I have a few phillips 12at7's laying around if that would be better. But wont this effect the trem oscillator as its the other triode of that tube?

Thanks!
-Josh
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Stevem
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Re: Princeton reverb bad distortion

Post by Stevem »

Sorry, I forgot the Princtons do use all 12ax7 tubes!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Deric
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Re: Princeton reverb bad distortion

Post by Deric »

Once your voltages are sorted out...

Adding a very large (470k - 1M) grid stopper to the phase inverter can do wonders for the overdrive/distortion when cranked.
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didit
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Re: Princeton reverb bad distortion

Post by didit »

Past success moving PI B+ supply up to the "320V" node on the AA1164 schematic. Grid resistors on the PI and 6V6s improves it, as already suggested. And increasing PI load from 56K to 75K or even 100K also cleans up.

12AX7 works for me.

Google cathodyne PI. Some good reading.

Best .. Ian
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