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Repairing a TBR400 - tips and replacement part suggestions [message #29142] Tue, 24 October 2023 10:11
weezykid is currently offline  weezykid
Messages: 9
Registered: October 2023
Location: PA
Junior Member
Hello all,

New to the board, but not to amp repair, but prefer to work on tube amps usually.

This amp came to me from a friend and it is blowing fuses when powered on. After some testing and inspection, I have found it is in the line of the red wires from the transformer. Bridge rectifier test good, 10000uf caps test good (but have a slight bulge and since they are 23 year old, may replace) with my blue esr. R314 and R337 were dark, board is a little toasty under those resistors so started testing around that area and find that the a970 (Q11 on the board, Q311 on the schem) is testing bad. However they are not available anymore and need to source a replacement.

Any suggestions on a replacement to the a970? Anyone have a newer schem than the one dated 4/16/2000 and also any update sheets as well?

And any other suggestions on things to look for in this model while I have it open?

Thank you!

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