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Author:  M. Gregg [ 17 May 2020, 12:33 ]
Post subject:  Diac

OK a question I cannot answer because I don't have any diac's.

I was just thinking about voltage clamps where suggestions have been made to use back to back Zener's across the audio output to clamp any DC voltage that may appear on the output of a tube preamp should the output cap fail. This I find is not that good YMMV.

My question is what would happen if you put a Diac across the audio output a bit like a neon? where a neon would clamp at approx. 80-90v a diac would clamp at 30-40V. Would the diac be "invisible" to the audio signal and clamp the output into a safe zone if the output cap failed?

M. Gregg

Author:  gofar99 [ 18 May 2020, 10:25 ]
Post subject:  Re: Diac

Good question. I don't know either. Does anyone know? But in over 50 years of audio builds I have never had a preamp output cap fail. I don't include protection for such events in my designs. There are far more likely failures that might do harm. Output tube in a preamp or power amp shorting internally and causing a huge spike can cause serious damage to speaker systems....particularly those with modest capability tweeters. Heater to cathode arcs in SRPP and similar designs can do the same. Those I do build in protection for.

Good listening

Author:  Soundbrigade [ 22 May 2020, 09:58 ]
Post subject:  Re: Diac

I have a bunch of Diacs myself, so a good answer could come in handy ... :D

The only application I've seen is in those simple triac AC-regulators:


Do a data sheet make any sense?

However when looking at the parameters, the breakover voltage is approx 30V. Had it been a few Volts it could have made a nice element for setting the bias ... but wait a minute. Could it be useful instead of bias resistor for OP tubes??!! :idea:

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