Adcom GFA-565 Capacitor Replacement

when I change out the leaky electrolytic capacitors between the reference diodes on the driver board, is there a certain type that I want to go to?
you mentioned the reference diodes (6.9 volt temp compensated Zeners) and the bias control transistors (MPS-A63 and MPS-A13 will need to be replaced? any type or part number I should go with for the replacements? thanks a bunch

I found this article about the amps that really explains the issue with these amps (both the GFA-565 AND the GFA-585) better than any of the posts here:

http://www.jazzfest.tyrell-corp.com/stuff/repair_adcom_gfa-565_gfa-585.htm

I just bought Adcom GFA-565 monoblocks and they thump the speakers on startup, but after that I'm not finding any problems. Is this a problem that can be fixed? According to Adcom, this is "normal" for these amps (yes I have that in writing). Is this true? And is this different than thumping in use, as noted above? I would like them NOT to thump on my Maggies.
Thanks,
Gary

The thump is caused by a dc voltage offset (as you said dc accross the speaker). This offset is usually caused by the leakage of electrolytic capacitors accross the voltage reference diodes on the driver board. The capacitors are 25volts, 220mf, cost about 79 cents a piece (there are four of them to replace). However, when this happens, usually the reference diodes (6.9 volt temp compensated Zeners) or the bias control transistors (MPS-A63 and MPS-A13) also need replacement. Your technician is full of it, the power supply capacitors are very durable, and most likely are not the problem. By the way, the power supply capacitors, 120 volts, 36000mf, are very expensive, about $90 a piece, and are difficult to find. Your best solution might be to search on the web, e.g. Ebay, for Adcom repair services, which can cost you a couple of hundred bucks per amplifier.

Greg sez

“Come on, Paul, tsk, tsk. Lytics are fine”

I thought this was an “audiophile” forum ;-)

“Easy to diy -- BUT if in doubt, go to technician.”

The tech is telling him “boat anchors” remember? Best stay far away from that tech – sounds like a shady character.

“It has to be electrolytic for the main power supply caps”

Nope – I used motor run caps in power supplies and they are the bomb. For the adcom there prolly won’t be enough space to go this route though.

It has to be electrolytic for the main power supply caps. Easy $5 job to do yourself if you are adventurous.

I think I would try contacting Adcom directly. Try one of the links off of their sebsite. Here ya go:

http://www.adcom.com/support.aspx

Enjoy,

TIC

Pauly sez:

Get film caps rather than electrolytic ...

Come on, Paul, tsk, tsk. Lytics are fine, same mF, higher/same voltage as noted.
Couple ("bypass")with suitable films if needed.
Easy to diy -- BUT if in doubt, go to technician.
Cheers

power supply caps might need to be electrolytic(???)(@30,000uf might be hard to find in a film cap & a bit pricey)

Here's where you want to go:
Musical Concepts Adcom Mods
If you don't want to spring for the full mod service (I would), ask them to simply recap them - maybe they'll give you a break.

Have a look at the value (MF and voltage) and get any with same MF and same or higher voltage.

Get film caps rather than electrolytic ...

regards
Paul