Metropoulos Forum

Hello  all. I just finished wiring up my amp and I'm having trouble with it. I would greatly appreciate any help you can give me.  

I'm not getting any sound out of channel 2. Channel 1 works. 

I wired up an input jack to alligator clips. It Worked on V1 pin 7 but not on pin 2. V2 pin 2 worked as did the wiper on the treble pot. 

I am biasing using a bias meter. I get no reading at idle. When I pass signal through the amp, the meter registers amperage. 

Any ideas?  Again, thank you for any help. 

Two problems.

One on the wiring of the input/grid wire of V1a or to mixers and the other probably biased to cold at the moment.

Need info on build, parts, spec and some pictures..............

Hey Neil,
Thanks for the help.

I am building a 1986. Marstran 1202-118 power transformer, marstran 784-139 output transformer, marstran c1999 choke. I turned the bias pot completely clockwise and still no bias meter reading at idle.

Normally a 220k bias feed resistor for that PT,

Suggest you pick up the bias feed direct off one of the HT lugs on the PT, not the rectifier (those rectifers are so and so s to solder to!).

Check your joints on channel two (chopstick if needed to see if you have a dry one!).

Check your bias ground

How does channel 1 sound? Clips?

Is the bias feed resistor the 150k i currently have in there at the corner of the board? I loosely followed George metro's layout.

I was able to solder to the rectifier. I roughed it up pretty good with a dremmel.

Could my problem with channel 2 be a bad .022 capacitor?

The bias is grounded. I checked for continuity with my multimeter. Channel 1 sounds a little thin to my ear. I'm not really set up for recordings right now.

Ok,
I got my bias straight.

I started out by shocking the hell out of myself. I then swapped out the 150k for a 220k resistor. That got me into the right range. Now I'm dealing the second channel.

One at a time, I swapped out the first .022 cap, the 220uf and 820 resistor, preamp tubes, andthe volume pot. Still doesnt work. The input jacks are wired correctly.

Im building the bass circuit. I tied together pins 3 and 8 on the first tube socket. Is this correct?

V1 readings are
Pin 1: 162
Pin 3: 1.3
Pin 4: 3.08
Pin 5: 3.08
Pin 6: 170
Pin 8: 1.3
Pin 9: 3.08

Post a pic of the input jack wiring too.

It's a little blurry. I can try to get another picture if u can make this out. These are the jacks for the second channel.

The input jacks and V1 voltages look okay.

If you haven't already, check continuity of channel 2 signal path:
- from channel 2 input jacks to 68k grid resistors
- from grid resistors to V1 pin 2
- from pot side of first coupling cap to channel 2 volume pot lug 1
- from channel 2 volume pot lug 2 to mixer resistor

Also, make sure V1 pin holders are tight (pins 1 and 2). The problem has to be before the wire from the mixers to V2 pin 2 so it shouldn't be too hard to find.

Very frustrating. Everything looks and tests to be wired correctly. I'll try again tomorrow. Ill probably replace the v1 socket.

I had a similar problem with an amp that was fine, then when I secured the board to the chassis, no sound.
In my case the nut in the middle of the board by the first coupling cap pinched and shorted the underside buss wire when I cranked it down.
Might be the problem.