Deluxe 112 oscillates

[Alex R]

Useful info here, which I used to solve the problem on this thread https://music-electronics-forum.com/...tenance-troubl...

[Alex R]

Oh sorry not to respond. This is a revision of the Williamson design. I was building a couple for a client, he supplied some lethal 50s DIY monoblocs with...

[Alex R]

Okeydokey I fixed it thanks to g1, with further help from this thread https://music-electronics-forum.com/...aintenance-tro...

[Alex R]

Ah thank you, that really helps, my theory isn't quite as good as it should be, now I have a line of enquiry to follow. I'll be back in the shop on monday...

[Alex R]

... alas I chucked the old zeners away after the first time I replaced them so I can't check that.

Oh I also removed the power amp in and headphone...

[Alex R]

Well friends this thing seemed to settle down in the end, but clearly I hadn't found the root problem because it came back to me after a few weeks having...

[Alex R]

Many thanks for the helpful replies. In answer - yes I too think they are 47R not 470R; no load was connected, and the bulb is 60 watt.

So it...

[Alex R]

Hi all, not been in here for ages but this one has stumped me. I tried to attach the service manual, hope it worked.

OK so this Fender Deluxe...

[Alex R]

sorry, answered my own question. Please delete thread if I don't manage to!

[Alex R]

I just had a guy in with one of these Bassbreaker 15 jobs. Same problem (redplating due to shorted zener), same solution (remove zeners on cathodes altogether)....

[Alex R]

Many thanks for the responses. You guys were right about the transformer - thanks for the guidance. It led me to clip in a spare transformer - and hey presto,...

[Alex R]

OK I came back to this amp and moved the speaker ground to the normal place, then tried tapping the NFB off each point in turn. The lower the impedance the...

[Alex R]

Thank you. This is a promising line of enquiry. When I get back to it I'll connect it normally and see what happens....

[Alex R]

Dur. Thanks Enzo. Currently on the bench is an AMI AA, I guess abut 1950. Blessedly simple and mono. This one too lacks screen resistors and uses the same...

[Alex R]

oh one other thing - screens connected to plates? Isn't that triode operation? Wossatabout?

[Alex R]

Many thanks for this. I did check the windings and I think reconstructed the tap order correctly. But the grounded 4 ohm tap - yes that could be an issue...

[Alex R]

WE have here a schematic you might have to pay money to get elsewhere. It's one of the stereo power amps in an AMI Continental. Early 60s jukebox amp. They...

[Alex R]

Ah of course, the bias voltage, dur. Thanks Enzo!...

[Alex R]

Thanks, yes fair enough - I must be being dim - but what about the signal?

[Alex R]

*diodes lol

[Alex R]

Have a look at this - power stage on a Bugera 333XL. What are D1 and D2 for? Control grid to ground? I know they'd only remove half the wave...