Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dwp on July 29, 2010, 09:32:30 pm
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Hey somebody wants me to build them a Princeton Reverb, I have no experience with this amp. (thought it was cathode bias, is not!)
Questions please
1. Is this the perfect practice size amp for someone who wants reverb and only wants to rattle stuff sometimes?
2. do you install a variable pot type resistor set up in lieu of 22K at the Bias board, or vary the B-? (10Kpot?)
3. do you still use the combo cap can with no ill effects with common ground to preamp?
4. plus/delta anyone?
thanks in advance, information always appreciated, often adhered to, dwp
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A bunch of us did Princeton Reverb builds over the past couple of years. There's a long thread in the Archives with bnwitt's Hoffman-style layout, etc.
I built two and a SEARCH should produce build-threads with pics, schematics and layouts on both of them. Used a cap can in both (hole was already there in the chassis), but used separate filter caps on the edge of the board for the preap & PI.
"Perfect practice size amp"? Depends... It does the clean Blackface tone beautifully IMHO. Stock, it doesn't "sing" by itself (also my humble opinion). Takes pedals nicely though.
Mods to try:
Adjustable bias
25K Mid pot
Lower coupling caps between PI and power tubes
Move PI "up" one node on power rail (debatable)
Fiddle with (i.e. lower) one or more cathode bypass caps
Lots of guys mess with the tone stack cap values (.033 / .022 seems popular)
Shielded cable to reverb/tremolo pedal
A SEARCH here, on AMPAGE and/or the Fender Discussion Page will turn up lots more opinions and ideas. Maybe more than you really want - it's a very popular amp.
FWIW Weber's 10F150-T is great in this amp (more HO :wink:)
Cheers,
Chip
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Also a 'mod' I just did was to add an IRF820 source follower to the trem circuit, which (lowers the output impedance of the LFO and) makes the trem smoother and quieter than the stock BFPR trem circuit (which is just one triode and a few caps and resistors)
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1. Is this the perfect practice size amp for someone who wants reverb and only wants to rattle stuff sometimes? Yes. Also, a fine gigging amp: boost preamp gain; RAW control; 6L6; 12" speaker. Great vintage Fender clean tone; overdrive available & packs a wallop in a small package.
2. do you install a variable pot type resistor set up in lieu of 22K at the Bias board, or vary the B-? (10Kpot?) Yes. And the bias pot will allow you to bias for 6V6 ot 6L6. Have not varied B+, but that sounds like an option.
3. do you still use the combo cap can with no ill effects with common ground to preamp? Yes, my re-build was DEAD quiet.
4. plus/delta anyone? No comprende.
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The AA1164 is my favourite amp.I add a Raw control and rock out.But they are not a quiet amp unless you use a low efficiency 10" speaker.
With a 1-12 they can be very loud and punchy.
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#1 No one's said this yet, but in (IMO) it's original configuration (15W OT, 10" alnico 25w speaker) it's not loud enough to gig with in a medium sized bar (i.e. any place a Deluxe Reverb would handle) unmic'd.
#2 It's always a good idea to install an adjustable bias circuit when there's not one in a fixed bias amp.
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thanks all for the info, exactly the input I'm looking for. Will review the "search" again, I would like to convert to Hoffman board, without straining my brain would be great. Beings as how someone is requesting it, and I've never built or even played one, slight disadvantage
"Plus/Delta"....That's where you go around the room after you've just sat through a grueling, or boring, two hour new age contracting work plan meeting, or any meeting. you ask everyone to list the their opinion of things that yielded a positive outcome (plus) or the negative things (delta) so you can all strive to improve everyone's meeting experience....might even stem directly from " The Toyota Way".......
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I built one, and it really turned out great, even though I'm not a Fender guy. I did add a mid pot on the rear faceplate to lose some of the scooped the mids I didn't like. And it's hum free ( don't have a clue how I managed that)