[RWood]

Hi,

Hello, first time poster here. I have searched for this board diagram but need some help. I'm repairing a friend's ST70 which has the AVA board installed. The problem is with a component (or possibly several) on the driver board. It would be a help to me if I could get the component layout and/or the schematic. This PC-189a board uses a pair of 6GW8s.

The initial problem with the amp was an "event" that led to the meltdown of one channel's bias sensing resistors. I imagine it was a runaway tube, and it did not help that there was a 20A fuse installed in the amp, which never did blow! Anyway, it was pretty much a charred mess around that tube socket. I have replaced the socket, shrinkwrapped several of the burnt wires and rewired it. The power tubes on that side actually work - I jumped the grids from the good side over to the bad and I do get amplification, but not though that side's driver circuit.

I tried comparing voltage readings from one side of the board

to the other but since they are mirror images I am having a hard time. Hence the request. If anyone can either post a link or attach an image I would be grateful!

Richard

[RWood]

Found it. Audio Basics, August 1991.

here is the link if anyone needs this in the future:

http://www.avahifi.com/images/avahifi/root/audio_basics/ab_pdf/ab1991-09.pdf

[avahifi]

If you need it, we can supply the complete build manual for the Super 70 or Super 70i rebuild kit for the ST-70 as a .pdf file at no charge.

Just contact me with your e-mail address and verify which version of the AVA rebuild you actually are dealing with.

20 amp fuse!  Wow, I bet that really made it sound good.   

Should be 3 amp slo blow fuse.

By the way, we never used 6GW8 tubes.  The original Super 70 used the original 7199 tubes. The Super 70i changed to 6GH8A tubes after 7199s became unavailable.

Regards,

Frank Van Alstine