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AUDIO FORUMS >> TROUBLESHOOTING >> SE84B questions about disconnected bias switch
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Message started by quietglow on 05/12/26 at 18:27:11

Title: SE84B questions about disconnected bias switch
Post by quietglow on 05/12/26 at 18:27:11

Hi folks,

I've had an SE84B (#180) for about a decade. The person I originally got it from gave it to me because "it had a buzz sometimes." I figured it was filter caps, but the buzz was very intermittent, and after I listened to it for a bit, it went away. I have been happily listening to it since. A few days ago, the noise came back. It only happens when the amp has been on for a few hours, is in both channels, and it goes away the second you flip the power off. Again, I figure it's probably filter caps. I am going to replace those soon.

While I was just in the amp, though, I noticed that the bias switch has been disconnected and the resistors were just left hanging there. Was this the work of Decware? Seems like maybe not a good idea to have those resistors just hanging there not terminated, no? ~~Pics attached.~~ Looks like I cannot post images yet. So: the resistors which are attached to two of the lugs of the bias switch have been snipped at the switch and are bent back, floating in space (very close to the output trannies)

thanks for any insight! (including if you think I am off on the filter caps)

I should have added: I have recently refreshed all the tubes and I have switched out tubes when it's making the buzz with old ones and its unchanged. So it's not tube related.

Title: Re: SE84B questions about disconnected bias switch
Post by CAJames on 05/12/26 at 23:52:50

It seems like the input tube needs a cathode bias resistor. Well, maybe need is too strong because the amp is working without one, but it seems like the input tube should have a bias resistor. JMO. Also JMO, but I usually associate bad filter caps more with hum than buzz. But I have limited experience with that, fortunately. Let us know how it goes.