Tube Amp Archive

Just plugged in the tank. Static is still there and reverb sounds great!

The static comes through whether the tank is connected or not. I was just messing with it and realized that it only happens on the vibrato channel. I plugged into the normal channel and it sounds fine. For some reason I thought it was both, my mistake. Yeah on mojotone the tranny is only like 12 buc...

Any way to test the transformer without replacing it?

Hi everyone! Hoping somebody can help me troubleahoot this thing. The amp in question is a 65 blackface ab763 clone bought from Marsh, in kit form. The only things that veer away from the original circuit are a master volume and a 2/4/8ohm output tranny. I built this amp myself about 5 years ago and...

Ok I will do as you suggest. Thanks for the advise. Anyone know where I can get one of these c15's if I need to? It looks like a white rectangular box. Or will any cap with the same values work?

ampgeek wrote:
Soooo...170 volts AC upstream of C15 and 170 millivolts AC downstream of C15. Yes?
Dave O.

Actually its 170V on one side and 0V on the other. Reads about 174mV at the junction of c15, r7, and d1. Would this indicate that c15 is bad?

When I have it set to volts I dont get a reading. Its less than a volt. But when I stuck it into the wall socket it read fine. The only way there is any reading but zero is in millivolts. I would suspect a faulty meter as well but doesnt good reading at the wall socket confirm that it is functioning...

c15 is 170vac. Same as the standby switch like you said.

oh, and wall socket is 116vac

The only way I get a reading on pin 5 with everything turned on is if I set the mm to 2000m vdc. It starts at about 50 and then keeps climbing past 300 but by then the tubes are red hot and smoking so I shut it down. This is with the tubes in. Without tubes I get about -8 millivolts dc. On Pin 5 (g...

Well... Got a new set of tubes and more of the same. Red plating like crazy.
Anyone care to take a whack at which cap is the bias cap?

Thanks for everyones input so far.

yeah sorry i tried to delete that post after i realized but was unsuccessful

This is the correct schematic, but its hardly legible. I noticed the pcb # didnt match up on the other.

Yes switched it over to dc when i didnt get a reading but still got nothing. And its definately not supposed to be millivolts? mVDC?

I had the meter set to 200vac.

I checked the diodes earlier and they seemed fine, got a reading in one direction and infinity in the other.

I cannot get any of these measurements. they are all less than a volt.