Is SD a Schottky Diode in this schematic?

[jduffy]

I've been looking at old posts for a simple SET schematic for an EL34 tube and bumped into this one.

Near the output transformer is a diode with the letters SD. Is this a Schottky Diode and if so, what would it's value be?

[zigzagflux]

Looks like the diode is there in an attempt to provide channel to channel isolation (keepting the right and left channel PS from affecting each other). So, yes, it looks like the intent was to use a schottky diode.

IMO, I would say a schottky is not needed in this application, and would probably not use it. Separate R-C networks to each channel would be better. If you want to keep it, though, I would think you should have a capacitor immediately after the diode.

[EC8010]

SD could mean "silicon diode" just as easily as "Schottky diode". No matter, the idea is misguided. There's no way the diode can provide isolation unless one channel's load current drops to zero, and since that will only happen when the output stage is clipping, I don't see a lot of point in fretting about it. Ditch the diode...

[ulibub]

Don't know what this should be, in my opinion it is completely useless. The more, if it should be a schottky diode, which genuinely is a low-voltage device. Also, for isolationg each channel from crosstalk of the other via the psu, it is completely useless. Since the AC produced on the tube's plate appears as a modulation of its quiescent current (no tube conducts true AC!), so you have as the result a varying forward continuous current through the diode, so that the AC signal is completely transferred into tu PSU - as if the diode wasn't there. The only way to avoid crosstalk via the PSU is to use 2 separate supply rails. Also, the nonlinear characteristic of this diode adds additional distortion to the power stage.

Simply forget this diode. Its nonsense.

Uli

[kevinkr]

Couldn't agree more, the diode is superfluous and as was pointed out might slightly compromise linearity..

[Wavebourn]

I do not see any meaning of this diode. However, if it was used from plate to ground im push-pull amp (2 of them, for each half of a primary) it could protect the output transformer from damage when running loud without a load connected, but as drawn it is meaningless.

[tubee]

Maybe the designer wants to protect the PS from high positive voltage kickback when the transformer winding cannot get rid of its energy. Only a guess. Better then would be a zobel accros winding (R + C in series)

[jduffy]

Thanks for the help guys. Much appreciated.

[kevinkr]

Originally posted by tubee
Maybe the designer wants to protect the PS from high positive voltage kickback when the transformer winding cannot get rid of its energy. Snip

And blow up the more expensive output transformer instead...

[tjl]

SD is what we call SILICON DIODE as EC8010 say, but not schottky diode, schottky diode cannot withstand plate voltage as high as 380V, 50-75V almost the maximum rating for general purpose type.

but if use Silicon Diode as 1N4007 can withstand up to 1kv /1A, or use fast recovery diode as FR157 for maximum 1kv/1.5A rating.

Using silicon diode for B+ separating power supply can reduce crosstalk between each channel as ULIBUB say.

WE always use two diode in series connection for safety reason.