one power tube slowly getting red

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one power tube slowly getting red

Postby demundo on Sun Jul 07, 2013 4:25 pm

I have 71 dr103 and one tube slowly gets red on the plates. it is always this socket no matter which tube I switch around. using rca 6ca7's . sometimes the ht fuse will blow. nothing inside looks burned or out of line. could the ot be checking out? cab impedance is right, voltage selector on 115v.
"honey,that's not new, i've had that amp for 2 years!"
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Re: one power tube slowly getting red

Postby OldSchoolDave on Sun Jul 07, 2013 4:50 pm

I'm also wresting with a "hot socket" on my 1969 DR504. Am considering individual trim pots on the power tubes, to allow for closer bias-ing.

You should (carefully) check voltage & mA at each tube on yours. I "cheat" and use a Weber Bias-Rite. Are you controlling the voltage coming in from the wall? I've been using APC Power Conditioners for my vintage amps - some set to 120v and others to 110v, depending on the amp.

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