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blionb 8th November 2012 08:57 PM

Weber 6m45p high pitch squeal
Hi Everyone! I am a first time amp builder with more digital experience than analog. I am building a Weber 6m45p kit and I am at the point of biasing the tubes. I am using the 1Ohm resistor method. The voltage on pin 5 of my power tubes start at 515V and as I watch the power across the 1Ohm resistor it starts a about 3mW, at around 7mW or so, it jumps to 11mW and it starts to squeal at a high pitch. From what I have read this is oscillation(?). Some of the methods I have read on line do not seem to fix my problem at all. I triple checked my wiring of the output transformer and all seems well. I am going to go over my wiring again to see if I missed anything. In the mean time, can anyone suggest tests, measurements, diagnostic things I could do to try to track it down? Thanks in advance. Links below:

DF96 8th November 2012 09:22 PM

This should be in the Instruments and Amps section.

Temporarily disconnect one end of R31, the feedback resistor. If this stops the oscillation then you have probably wired the OPT wrongly.

blionb 12th November 2012 04:41 PM

I did have the OPT wired incorrectly. I swapped the blue and brown wires from the OPT to the EL34s and the oscillation stopped. Now I have a different problem/question, but I will take it to the correct forum this time. Thanks for your response!

kevinkr 12th November 2012 04:54 PM

:cop: Moved to Instruments & Amplifiers per forum policy, see below:


Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum


Instruments and Amps Everything that makes music, Especially including instrument amps.

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