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I like the bridge PCB, is that something new on the market?

Its quite possible that the scope resolution initially led me to believe that it was flat lining, my bad. Good call on the resistors, mine look toasty.

UPDATE So I took some freeze spray to the driver board and it made no difference but applying the spray to the back plane produced some interesting results the further down the negative bank I went. Have a look at a clip that I made at that time, I hope the link works...

Can anyone point me in the direction of one? The service manuals are plentiful enough but not the OM. I`d like to read up on some of the more unusual features of this preamp. TIA :)

Yes Lee, the amp will work just fine from a cold start and then go dead depending on how much its putting out. With lower output (20vrms@8R) the amp functions for longer periods.

I re-flowed every component on the drive board and inspected the back plane for anything obvious. I did notice that the transformer secondary wires were only being held to the bridge rectifier through the holes in the tabs, they werent properly soldered and both worked themselves loose...

Good points:)

Its more a matter of discretionary spending than being broke. Im not one to half ass anything least of which my sound system. This amp wont get within 20 feet of my $5000 speakers in its present state. If all that is needed to rectify the issue is a $1.00 transitor, Im all for it.

How I`d love to but money is extremely tight these days :( I think Ill start with Joe`s first two suggestions, they make sense and wont cost me anything but time.

Hi All, I just picked up one of these hopefully to mate with my 700s2. Its in really nice original, unmolested condition. No issues with the left channel but the right channel will intermitantly flat line, under an 8 ohm load. It will run up to 49 volts before clipping but then go dead. An...

$7 500 for a 700, $20 000 for a D-500, WTF...

Thanks for the reply. Is that Mouser switch a drop-in replacement ie no mods to either switch or chassis required?

I found an old picture, it looks like there is indeed another set of contacts on the opposite side. Why no capacitor I wonder?

That would be worth investigating. I cant recall if the power switch has an unused section, but if it does I cant imagine why those contacts werent doubled up in the first place. The amp is racked, in service and precisely calibrated for gain relative to another amp. Before performing any kind...

Thats great news! Would a .1uf cap be ok tacked across the contacts? Im a little surprised that the switched failed on an amp that has essentially been stored for the last 40 years. Ill report back once repaired. Thank you kindly for all the replies and suggestions )

Hi All, The power switch in my 700 series ii has shorted closed :( Is this a common issue? A cursory search turned up a few replacement options for the 700B but nothing for the series ii. Am I SOL?

Sure there is :)

I think your findings will be, pardon the pun, amplified proportionally once you get the PL into your main system which is much more revealing than what you are currently testing with. Component break-in is a real phenomenon. It is more apparent and quantifiable in loudspeakers when changes in...

Apologies for resurrecting an old thread but I finally re-visited this issue and with Joe`s help I was able to resolved it. The amp was doing LFE duty all of this time so the hum wasnt really an issue until I decided one day to run it full range on some JBL L80T`s that I just restored. The JBLs...