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

hi
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.
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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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