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previous: Jim S. The diodes act as voltage spike pro... -- 8/3/1999 4:18 PM View Thread

Re: Trainwreck pages..............diodes from plate to ground?

8/3/1999 9:49 PM
John StokesRe: Trainwreck pages..............diodes from plate to ground?
There is some misinformation here. The diodes are in series to develop a 3000 PIV to keep them from zener breakdown during normal operation. If you look at the plate waveform with an o-scope, you will see that when the tubes on a side are cutting off (tubes on the other side are turning on hard), the plate voltage rises to double (or more, depending on leakage inductance and load quirks) the center tap voltage. The diodes are there to conduct if the plate voltage goes negative (clamping the voltage at ground to prevent it from going negative), again, due to leakage inductance and load quirks. One of the problems with this is if things are misbehaved, the diodes get whacked with fairly high peak currents and eventually fail to shorted condition. IMO, if you were going to do this, I'd put a 100 ohm current limiting resistor in series with the diode string.

 
Replies:
AD When the diodes are in series, the ... -- 8/3/1999 10:03 PM
Reid Kneeland John:They may also ... -- 8/3/1999 10:26 PM
R.G. There is an inevitable leakage indu... -- 8/3/1999 11:15 PM