Princeton Reverb clone with 12" speaker?

[tubeswell]

After intermittently chugging away at this for some months I still can't get rid of the aforementioned hum. I re-did the ground to a brass plate ground exactly like the BFPR layout, then I tried the split ground - hoffman style with seperate pre-amp filter cap grounded with the pre-amp, and now I tried a bus wire split ground. elevated heater then no elevated heater. Heater with CT ground, and heater with 2 x 100R grounds. Every time I've got the same symptoms. Hummy until about 5 on the vol dial, when it goes quiet, then hummy again as you turn it past 6.

I never have this problem with my own scratch-built amps. I wondering now whether its a bad cap can or something.

[JoeM]

Are you sure it's power supply hum? Weird effect, your volume control is almost acting like a hum balance control. Two stages with the hum out of phase, and turning up the volume control balances the hum so it nulls out? Bad heater connection somewhere?

[axpro]

I just finished my PRinceton HP varient today as well. aside from an exploding cap and afaulty copper cap rectifier, it's pretty cool. sounds good, reverb is noisy, but i need to work out a few lead dress issues. When i originally tested the chassis and did my burn-in test, i had it through a marshall 4-12 (i think it had a crap speaker... not my cab) and the bass sounded too farty. I pulled the cathode bypass cap in the first stage,a nd it was a little better.

With the Weber Speaker it is pretty good though! I do need to clean up the lead dress a bit, and I want to sh ield a few runs to cut back more on noise.

Then just find and eliminate the reverb hum.

AND

find a way to deepen the trem a touch and slow it down a bit.

Otherwise, s'allright!

Sounds GREAT with my PRS singlecut mutt and my OCD.

[Bruce / Mission Amps]

After intermittently chugging away at this for some months I still can't get rid of the aforementioned hum. I re-did the ground to a brass plate ground exactly like the BFPR layout, then I tried the split ground - hoffman style with seperate pre-amp filter cap grounded with the pre-amp, and now I tried a bus wire split ground. elevated heater then no elevated heater. Heater with CT ground, and heater with 2 x 100R grounds. Every time I've got the same symptoms. Hummy until about 5 on the vol dial, when it goes quiet, then hummy again as you turn it past 6.

I never have this problem with my own scratch-built amps. I wondering now whether its a bad cap can or something.

I had an amp that did this to me for a few days of off and on head scratching and it turned out to be a bad volume pot... I would have never figured that until I got frustrated and broke the grounded lug off and then needing to replace it.
Also had one that did this until I replaced the Alpha reverb pot with a lower value one... yup, it reduced the reverb a little bit at high reverb levels but the hum was less then 1/2 as loud.

[tubeswell]

After thinking about what you were saying about hum-balance Joe, I went back and looked every thing over again and found it! - input jack wiring. I sorted that out and now it doesn't do the hum-balance trick with the vol anymore - its just a plain ol' hummer.

which narrows it down a bit

[JoeM]

After I had my Princeton baffle cut for a 12", I put an EVM 12L in. The amp was humming so I figured it was time for a re-cap, but even after that there was no change. Found out it only hummed when the amp was in the cab, the proximity of the huge magnet on the EV was causing the PI tube to hum somehow, all I needed to do to fix was use a different tube.

[tubeswell]

Just a conclusion to this chapter - I re-did the layout with my own board and separated the caps and put in the locally made PT. THis was up an running just over a month ago and with no hum whatsoever. funny that

[el1psey]

hey, i just built this kit and put it in a homemade 12" combo cab with a tone tubby ceramic 12. sounds great, loud as hell. the switches and jacks are fine, the pots seem cheap, but they work. the Chinese 6V6s that came with the kit look seriously cheap; there is some kind of glue or caulk looking stuff squeezing out around the base of the tube that smelled like burning plastic when it got hot. the glass is painted black like they are hiding something. they sounded good, but i replaced them with JJ's to avoid the smell. i added a master volume, and replaced the 25mf bypass cap on the first gain stage with a 2.2mf because the bass was overbearing. i also raised the plate voltage on the PI, and converted the PI to fixed bias, which greatly improved clean headroom and sound, IMHO. (thanks Bruce, for the tip on using a 4m7 bias feed resistor!! it made my clipping nice and symmetric on the scope.)

[Casey4s]

I think these BFPRs sound teriffic with a 12" speaker. I built one a couple of years ago, although not a kit, and I used a 12" Alnico speaker and love the tone. I also added a Mid control, a presence control and speed & mix for the reverb, to mine for a bit more flexability. It's the amp in my avatar.

[frankeg]

Tubeswell, happy to hear you solved your hum problem. I wonder if you didn't have a faulty cap can. I've heard that is a more common problem these days.

elipsey, Where did you insert your master volume? Also, did you change the standard 1meg resistor on the PI?