Phonoland

The fuses on both driver brds are blowing ,would replacing both sets of xtors in the amplifier solve this problem?

Thanks In Advance
Mark

Hi Mark,

Yes it could be the transistors that are blowing the fuses, do they blow straight away?

Have you checked that the transistors are in the right location on the heatsink.

Regards
Alan Hood
ami-man
UK

Hi Allan,

Thanks for the reply,no,it does not blow them right away.It begins by "frying"a resistor adjacent to the fuse.I unhooked the wiring harness from the transistors and the problem disappears,so I'm going to replace both sets of xtors and see if that cures the problem.Everything appears to be original.

Thanks again for your interest and I'll let you know how things turn out.

Mark

Alan,
Replaced both sets of xtors to no avail.I'm finding that there is 36 volts on the output to the right speaker and not on the left.Perhaps there is a bad 2SA56 xtor letting 36v through?

Mark

The fuses are just flags, to tell you which transistors to replace. Did you read the book and set the bias voltage? Check the diode board attached to the heatsink. It was upgraded back then. I would only use good quality transistors, the cheap ones aren't worth the trouble. Don't forget the mica insulators.

Hi Mark,

Check out the voltages to your driver boards there should be +36 volts and -36 volts. If this is not the case then check out at the bridge rectifier and smoothing caps.

Regards

Alan Hood
ami-man
UK

Yes I have the +and- 36volts into the driver boards but the problem is that I'm getting +36 volts out on the right driver board to the speaker when there should be little or no voltage. Again,I'm wondering if a bad 2SA56 xtor would be the cause?

Mark

There should be3 DC blocking capacitors between the transistors and the speakers. One is shorted if you measure 36 volts on the speaker (which can ruin the speaker).