Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: goldstache on October 03, 2022, 08:17:44 am

Title: Sunn Beta Lead DC develops on speaker jack
Post by: goldstache on October 03, 2022, 08:17:44 am

Trying to cure the ills in a Sunn Beta Lead.
I’ve recapped and replaced finals and voltage regulators on power amp board.
Had a nasty bit of DC on speaker output jack.
After all the above part swaps, it will act ok for about 5 mins then DC on output jack soars to +20vdc and there’s a nasty hum all a sudden!


Any ideas? I’ve tested bias transistor and all socketed transistors. The feedback IC (4558) has also been swapped.

Title: Re: Sunn Beta Lead DC develops on speaker jack
Post by: shooter on October 03, 2022, 09:04:06 am

i got metered internet and Doug's schematic is like a week to download so, after the 8th I might be able to help  :laugh:

Title: Re: Sunn Beta Lead DC develops on speaker jack
Post by: goldstache on October 03, 2022, 03:10:33 pm

Good news. Solved
Bad replacement 4558 in feedback loop. Swapped again, all is well.


Thanks