Switchable Rectifier

[hans-jörg]

Hello Gents,

could someone tell me how to switch from tube (EZ81) to solid state rectification? Or a link to a schematic where this is shown?
I asked Mr. Google, but with neg. answers.
I have a 2 wholer Liverpool and want to implement this feature, but in a save way.

Thank you in advance,

Hans-Jörg

[Stevem]

Will the amps power supply filters handle the extra 30 some odd volts that you will have with those SS recto`s?

[hans-jörg]

Will the amps power supply filters handle the extra 30 some odd volts that you will have with those SS recto`s?

Would say yes. there are 450V caps. Primary is 290 VAC.
Now there are 330VDC on the plates and around 310 VDC screens.

Hans-Jörg

[roberto]

Just copy the mesa boogie dual rectifier, schematics can be found on the web.

[hans-jörg]

I got it! Very simple, just a switch between.

Thank you very much!

Just a small question more: does the recti tube not suffer from heated cathode without load? Better pulled if not in use?

Best
Hans-Jörg

[sluckey]

Here are a couple options that are currently being discussed on Hoffman's forum. These are shown with a 5AR4 tube but will work with an EZ81 also. I would not be concerned about pulling the tube.

[hans-jörg]

Thank you Sluckey,
that´s a very good tip.

Best

Hans-Jörg

[gktamps]

Here's one way I've done this...

[hans-jörg]

by mistake

[hans-jörg]

@ gktamps:

yea, I saw it somewhere before. That's the simplest way I looked for.

Merci

Hans-Jörg

PS: I looked at the datasheet for this switch: it shows 250VAC !
Is that save for ~ 350VDC?

[pops]

If you use the bottom design on Hoffmans then should your rectifier tube short out the diodes will still allow the amp to work and the shorted tube will become a switch that is on. Unless you can hear the difference you won't even know it.

[M Fowler]

I followed Martin Mannings drawing.

[martin manning]

Leaving the cat out of it, that scheme has the SS diodes backing up the vacuum rectifier in vacuum mode, and the vacuum rectifier's heater disabled in SS mode. The switch is (mostly) handling low voltage too. It was my drawing originally, but Miles added his unique touch.

The '64 Custom Vibroverb schematic above runs the vacuum diodes in parallel... not a very good idea, IMO, since one of them is going to be doing most of the work.

[gktamps]

@ gktamps:


PS: I looked at the datasheet for this switch: it shows 250VAC !
Is that save for ~ 350VDC?

Hmmm. Good call. I copied this from a production amp in one of my 18 watt Marshall types several years ago, and while I never switch with power on, I think you are right; a higher capacity switch is in order.

I don't use switchable rectifiers anymore, either just using diode backup on the tube socket, or a solid state tube replacement if desired.

[hans-jörg]

@ gktamps:



I don't use switchable rectifiers anymore, either just using diode backup on the tube socket, or a solid state tube replacement if desired.

Hi,
I found out that the bigger companies mostly don´t care about safety and longevity but only about costs.
Never would use such a switch with STB On! My STB is in front of the recti double sided.
To be honest: I want check out which version I prefer more and that will be than fixed (I guess).

Thank you all,
Hans-Jörg