baby blue 'blues'

[Shannon Parks]

Hi, I have a Stereo 35 Rev B which I recently did an output valve bias adjustment on. I am only new to tube stuff and I foolishly left the amp on for an hour or so without a signal and with no load on the speaker output.

Hi Matt,

My gut instinct is that you might have mistakenly adjusted the negative feedback pot (R30 and R31) when biasing. This would be a bit easier to confuse on your Rev B board compared to the later revisions (ie I've done it myself). Also, did you disconnect or reconnect any of the wires? If the amp had started to oscillate wildly you would have heard it - even without an output load.

If by chance you might have adjusted R30 and R31, have everything diconnected from mains and drained. Then disconnect the feedback to J3-3 and J4-3. Then take resistance measurements to ground. Should be 20.3K (if an 8 ohm tap) or 28.3K (if from 16 ohm tap).

Let me know if any of this seems applicable, else we'll continue trouble-shooting. I wouldn't worry about your iron yet.

Antipodean Regards,
Shannon

[Shannon Parks]

I checked the ohm readings at J3-3 and J4-3 anyway, like you suggested, and I got readings of 28.1k on one side and 28.4k on the other. I'm running 8ohm speakers - is this the right setting?
How do I know if i'm using a 8 ohm tap or a 16 ohm tap? Is there more than one tap from the transformer , could you please clear this up for me?

Hi Matt,

Glad you got her up and going again! What make & model are these outputs?

Shannon

[Shannon Parks]

Hi Shannon, It's real hard to make out but I think I can see what looks to be Z-565 stamped on the side of one. They have cloth leads.
Hope this helps......Matt.

Hi Matt,

This is easy then, as they are original Z565 outputs from Dynaco. The yellow wire is the 16 ohm tap and the orange one is the 8 ohm. On mine, I just run the 16 ohm tap back to the NFB post. Sounds like you are all set up correctly.

Shannon