It is time: The Fisher TA-600
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Joined: Feb 2013
City: Irvington, NY
As Greg said, one of the output tubes is gassy or has grid emission. It goes into a thermal runaway condition where as it gets hotter, the plate current increases which makes it hotter.....
The Russian tubes are also probably run over their ratings, as the 7189 has a higher plate voltage rating than the EL84
The problem is compounded by the fact that there is a common cathode bias supply for all four tubes. If one tube draws excessive current, the negative bias only increases by only 1/4 the amount as if there were individual bias resistors.
(This post was last modified: 04-18-2017, 12:13 AM by Mondial.)
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RE: It is time: The Fisher TA-600 - by Mondial - 04-18-2017, 12:12 AM
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