Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: BigE on March 30, 2015, 08:25:07 am

Title: Ampeg V-4BH low output
Post by: BigE on March 30, 2015, 08:25:07 am

I've got an Ampeg V-4bh that suffered a fall from the cab it was sitting on.  Now there is hardly any output our of the mains.  Swapped Tubes and no change.  Chop-sticking doesn't reveal anything.  Can't see anything broken or loose.

Here are my voltages:

V1
1 - 220   6 - 218
2 - 0       7 - 0
3 - 3.7    8 - 1.8

V2
1 - 346    6 - 220
2 - 71     7 - 2.5
3 - 113   8 - 4.5

page 2 schematic:
V1:
1 - 230   6 - 270
2 - 0       7 - 50
3 - 1.7    8 - 102

v2:
1 - 281   6 - 276
2 - 0       7 - 0
3 - 15     8 - 15


Power tube voltages:
3 - 485
5 - -47
8 - 0

voltage at "bias" point in schematic is -48
+- 10v are right on
High voltage drops look OK.

Not sure where to start since I can trace signal all the way through the thing. And you do get output but you have to Max the thing to get any signal out.

Thanks in advance.

Title: Re: Ampeg V-4BH low output
Post by: shooter on March 30, 2015, 08:40:20 am

usually mechanical hits cause mechanical breaks, I'd still look for that.

Quote

I can trace signal all the way through the thing.

Listening or scoping?  I'd think either would show where the signal gets anemic

Title: Re: Ampeg V-4BH low output
Post by: BigE on March 30, 2015, 08:45:37 am

With a listener box i traced the signal.  I figured on the power tubes it would be non existant but it seemed pretty solid.