Princeton owners, you voltages please.

EMan

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If any of you folks happen to have (any) Princeton opened up and a few spare minutes, I'd appreciate some DC votage readings.

I'm really interested in the Phase Inverter section, and would like to get the B+ to that tube section, the plate voltage, the cathode voltage, and the voltage at the junction of the 1K ohm and 56K ohm resistors in the cathode leg.

I'd accept any other voltages anyone wants to add...and you can PM me if you don't want to litter this board with numbers.

Thanks!
 

Dacious

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Sorry for the slow reply Eman, about to pull mine apart this weekend to fit a new P-T with Oz primary. I'll get you before and after. I'm running it off a 240-117volt step-down transformer at present.
 

Bluesbob

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EMan, how come you don't look on the schematics at the Field Guide? Are you trying to find out how far the tolerances have drifted over the years? I mean, on the schematic for the AA964 Princeton it reads +63.8V (I think) at that junction. I know we get more juice now out of the wall, but that number should be in the ballpark. Or am I missing something?
 

EMan

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BluesBob - I have read comments (not here) that these printed PI voltage numbers are way off. I don't necessarily believe that is the case, and am looking at getting some 'real' numbers from folks that have this particular amp.
 

Dacious

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OK, my stepdown tranny is putting in exactly 115vac measured at the convenience outlet. I'd say it's running flat out, as it's only a 67va rated transformer.

Amp is running Sovtek 5U4GB, JJ 6V6s and all EH preamps for the 12AX7s and 12AT7. Seems quite healthy.

378vdc at the first filter cap section.

182vdc at the plate pin.

50.9v at the cathode, 48.8v at the junction of the two resistors. I haven't actually measured the resistors.

As far as I can tell it's a '80 - no stamp on the tube chart, looks like original Mallory silver electro filter can and 25/25 bypass, 70/50 bias cap, blue Astron poly caps. The codes on the trannies are all EIA-606-0xx. The speaker is a Blue Fender Special Design Eminence ceramic with a 1980 date code. I thought it might have been changed, now I think it's original. Pullboost volume, no tail on Fender logo.

This is with all controls turned to zero. I think this is pulling all the voltages down.

Ah - Houston we have a problem. When I turned the controls up to ten - bingo - tubes attempted to draw 40ma ea! It blew the fuse in the stepdown twice. Dropping volume and tones back to 4-5 keeps the fuse in it @ 32ma but it's very boomy.

I'd only played it on lowish volumes and it seemed very loud for a small amp on five. I think it's maybe the bias cap is bad.

I was going to do all the caps and fit a bias adjust anyway, so I'll do all that and get the readings again.
 
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Bluesbob

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Well, something's not right...

The Field Guide gives the last year for the Princeton as '79. So I guess they're wrong about that and they can probably be wrong about the other.
 

Dacious

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This is actually a Princeton Reverb. The voltages on the rube charts are with 5 volts of the Princeton in the phase inverter.
 

EMan

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Thanks Dacious, for taking the time to post these values. I appreciate it.

I think I might get a little beefier step down transformer..67 Watts isn't much! You could get another like the one you have, and run the two in parallel.

Thanks again!
 

Dacious

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No, it was just an old stepdown I've had for ages. I have a Weber multivolt primary tranny to drop in so I can plug it straight into domestic 240v here. This is a nice-looking unit, same formers and endbells plus copper tape as the originals, but about 1/3 as high again. Looks like it was made by the original company, if the stamps on it are any indication.

I think @ 100ma 660 volts plus an extra amp on the heater and rectifier circuits there's enough beef there to power a pair of 6V6s!
 




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