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Spec 2 bias (again??)

M

MRMICROPHONE

New Member
as received.JPG bad left.JPG good right.JPG Greetings! I think I've read all the relevant posts and still have a question. I am working on a Spec 2 that someone else has worked on. I upgraded all the TO-220's, electrolytics, and bias relays on the amp channels. I had an open R61 (thermal sense supply) and protection lamp on the meter board. After repair, I powered it up without issue and it plays in both channels. When I tried to set bias, I discovered that I cannot achieve the correct bias in the left channel; it is too low. The trim pot is fine. No problem on the right channel. Not surprisingly, the left channel is significantly cooler than the right, so I believe my bias readings are valid.

I noticed (remember, there is unknown repair history) that the left channel has two of the same bias diodes, unlike the right channel. Looking at the schematic, I see that it should be one STV3H and one STV4H. On the left channel, I have two diodes that are marked "6NA." Both have a yellow dot on the side.

Help?

I should also mention that the boards are a newer revision than the commonly-available service manual. I included a "before" picture so you can see the revision clearly.
 
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Thanks for the quick reply! I considered asking you directly, but thought this may help someone else later on.

Is the 6NA the same as an STV-4H or am I looking for two unobtainium parts instead of one? Is there any chance you have a data sheet for these or at least an original manufacturer?
 
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