Monkeymatic Acetone Princeton

[xtian]

I'm rebuilding this funky Japansese Acetone BASE-3 as a Princeton AA964.

[Blackburn]

Looks like fun!

[xtian]

What's the best, single switch mod for this circuit? V1 cathode bypass? NFB? Tone stack lift?

[printer2]

Depends what you need. If you want a cleaner signal switch out a bypass capacitor (for example), If you want the amp to be a little more dirty switch out the NFB.

[Blackburn]

For pre switching, that tone stack lift sounds pretty cool. Cathode bypass switches are alright, but I'd rather have a DPDT doing something along with a bypass cap, to increase its effect. You're good to go for the stock Princeton setup with depth and speed knobs already there. BF Princeton trem is to die for. Make that thing wiggle!

[xtian]

Q: How to 2mm eyelets work on 3mm G10?

A: Great, if you drill the back of the board, too!

[David Root]

A worthy effort! Frugality is good!

[David Root]

Sorry, double post.

[xtian]

Finished, and working very well, except that I have low output. Perhaps 70%. And this is with no NFB. Should definitely be louder.

Voltages look good, compared to the AA964 schematic (in general, I'm 10% higher). Except my cathodyne inverter voltages are not OK. Fender schematic is difficult to read. Is V2, pin 8 (cathode) supposed to be 65v or 6.5v? Merlin says the grid (pin 7) should be around 50v. My voltages are:

pin 6: 313vdc
pin 7: 6.94
pin 8: 11.3

Everything sounds great. No buzz, very low hum, bias trem works great.

JJ 6V6 have 422 on plates, and are biased at 0.023mA.

Just low output, as I said, like 7 out of 10.

Please help me figure out what's up with my cathodyne inverter.

[cbass]

Congrats.Cool old amp .Nice lookin build.
I think that piv 7 on the PI should be around 50voltsPin 8 is low to probably where the problem lies.ht double check the resistor values around it.

I built a Princeton reverbish type thing into an old univox amp.That I never though would be worth nothin.Now I see the prices steadily increasing its bringing close to 500 bucks now.

I trird every mod there is to that circuit and decded it sounded best pretty much stock.I think I used 2.2uf bypass caps and added a grid stopper to the PI

[xtian]

OK, I'm mostly stupid, but not all the way. I put in 5K6 load resistors instead of 56K. My space shuttle would have blown up on launch...

But now that I've fixed that, the amp sounds almost exactly the same! Not loud enough! Voltages look better on the cathodyne, but not perfect (259 plate, 29 grid, 82 cathode).

I put 1v p-p sine wave on the input, and turned up the volume until just before output distorts. I get 65v p-p going into the grids of the 6V6's, but only 20v p-p at the output into an 7R7 load. According to P = V^2 / R (converting 20v p-p gives me 7v RMS) this gives me about 6.4 watts at the output, which matches what I'm hearing.

But but but! My 6V6's are dissipating around 18 watts combined total, aren't they? 440v on the plates, 0.023mV across 1R resistors at the cathodes.

Could this mean the OT (it's the Japanese original) is a crappy POS?

[xtian]

Halp? Wondering if I should order a new OT.

[xtian]

Anyone? Haloo?

[martin manning]

Idle plate dissipation has very little to do with output power. How about measuring the impedance ratio of the OT and see what you get?

[Richie]

If your going to pull up the feedback resistor, ground the cathode resistor and bypass cap tail end. Don't go through the 47ohm resistor. This will make a slight bump up in it. What does the OT read?