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PostPosted: Thu Jan 25, 2018 6:04 am 
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Joined: Tue May 24, 2016 11:16 am
Posts: 104
Now in the process of finishing up a TMB18 kit. Noticed in the instructions warning about accidentally running amp with speaker disconnected could damage output transformer. Have observed some tube amps short output to ground if no speaker cable connected, and it makes sense given that tubes are current sources, a short to ground is better for the output transformer than an open circuit which can lead to high flyback (di/dt) voltage inside the transformer whereas a short keeps voltages low.

Furthermore, noticed that the switching speaker jacks that come with the TMB18 could be wired to short output if no speaker cable phone plug inserted in at least one of the jacks. The wiring logic is pretty simple. Any reason why it wouldn't be a good idea to do what many amp manufacturers do to help protect output transformer by using jack wiring logic to short output if no speaker cable connected?


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PostPosted: Thu Jan 25, 2018 11:14 am 
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Joined: Sun Jan 22, 2006 1:39 pm
Posts: 5984
Location: Richland, WA
I suppose that would be better than just leaving it open. Perhaps adding a large wattage resistor of the approximate impedance would be even better. Although that would complicate the wiring logic a bit.

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