Re: Bias Instability

Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

I have a rebuilt Dynaco ST 70 using a VTA mod board and a couple of issues have developed and any help you can give would be greatly appreciated.
1) One channel has begun to have a higher level of hiss or distortion than the other.
2) The same channel as described above has an unstable bias after the amp warms up. The bias will not remain stable - it fluctuates from .31 - .55 and never stays stable (i.e. the meter reading never sits at the same number for more than a second) The other channel bias reading sits solid as a rock.
The same channel as describe above had a tube that glowed bright orange and I replaced it with a new one. I thought that the output transformer was going so I got a new one and it has the same issue. These happened previously to me realizing that the bias is fluctuating upon warm up.
Thank you for your time and any advice you can give..
Regards,
Paul

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Topic - Re: Bias Instability - pwalker 09:12:37 04/21/07 (7)

Other things to check - Chris O 12:34:42 04/21/07 (2)

Re: Other things to check - pwalker 18:09:28 04/21/07 (1)

Re: Other things to check - BrassTeacher 22:47:15 04/21/07 (0)

Re: Bias Instability - pwalker 11:38:18 04/21/07 (0)

Sounds like a leaky coupling cap (nt) - Triode_Kingdom 10:09:34 04/21/07 (2)

Re: Sounds like a leaky coupling cap (nt) - pwalker 10:15:24 04/21/07 (1)

Capacitors block DC - Ron Oehlert 13:07:04 04/21/07 (0)

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