Diodes in parallel with GZ34?

[Opry Audio]

Hey y’all!

I’m considering adding some diodes in parallel to the rectifier tube in some of my amp designs. Will this ultimately affect the voltage drop across the tube? And thus affect the nice sag gotten from the tube itself? I like the idea of it as sort of a protection for rectifier tube failures but I don’t see it a whole lot and thinking this might be why. Thanks!

[pdf64]

Protection diodes go in series with each anode, not parallel.
1k5V PIV is required, eg 4x 1N4007 in total, 2 in series for each anode.
Rectifier valves last a lot better if hot switching standby arrangements are removed / amended to non hot switching.

[Opry Audio]

Protection diodes go in series, not parallel.

Duh. Yeah of course. I haven’t had coffee yet.

[Opry Audio]

The amp I have it in mind for does not have a standby switch. But what’s the different between hot switching and non hot switching?

[pdf64]

Don’t put the switch between the rectifier and the reservoir cap (+ test of amp).
As that’s hot switching, ie a hot, fully conducting rectifier has to charge up the cap in an instant.
That’s a common reason fuses can blow when standby is flipped.

It’s better to have rectifier, reservoir cap, standby, then rest of amp. See http://www.valvewizard.co.uk/standby.html

But even if someone thinks standby is a good idea, the slow smooth ramp up of HT voltage provided by a GZ34 does that job far better.

[Opry Audio]

So is this kind of thing not really suitable for a PR? I know the delayed warm up time of the GZ34 is part of the reason why it works well in this amp, and don’t want to hit the tubes with high voltage before they’re ready to conduct

[pdf64]

So is this kind of thing not really suitable for a PR? I know the delayed warm up time of the GZ34 is part of the reason why it works well in this amp, and don’t want to hit the tubes with high voltage before they’re ready to conduct

That won’t happen with a GZ34. It takes longer to warm up and conduct than the other valves.
The ‘hit’ (voltage or current spike) typically caused by standby is pointlessly nasty.

[Opry Audio]

Ah ok! I get it now. Does it matter which order the diodes are in relation to the tube, before or after? I see now that the tube will not start conducting HV to the rest of the amp until it’s warmed up regardless of the full wave rectifier being there.

I see some amps using only 2 BYD33V in series with the HV windings before the rectifier. Is this sufficient or are 4x in4007’s more efficient? I see that the max continuous voltage is 1k4v but it has higher current specs. 

[pdf64]

The silicon diodes are in series with each anode, see d1&2 https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-57-Deluxe-Schematic.pdf
If you’ve got those diodes then fine, I just mentioned 1N4007 as most techs have plenty handy.

[trobbins]

The reverse voltage capability of any ss diodes added in series with the valve diode anode depends on the power transformer secondary voltage being used - which you haven't yet identified.  It could be that one 1N4007 in series with GZ34 plate is ok, but often (depending on Tx voltage) two series 1N4007's are used.  Similarly one BYD33V may be fine, but even its PIV rating may be suspect - depending on the Tx voltage.

If possible, imho don't mount any such ss diodes to the GZ34 socket terminals - there is a reason why rectifier valves have unused terminals between anodes and cathode/heater terminals.

There was an early technique, called 'The Port Arthur Rectifier' from Gerald Weber Dec 2005, where ss diodes were added in parallel to valve diodes - that was prior to the now common series connection technique.
https://www.dalmura.com.au/static/Port%20Arthur%20Rectifier.pdf

[pdf64]

...There was an early technique, called 'The Port Arthur Rectifier' from Gerald Weber Dec 2005, where ss diodes were added in parallel to valve diodes - that was prior to the now common series connection technique.
https://www.dalmura.com.au/static/Port%20Arthur%20Rectifier.pdf

Ughh, that seems kinda wrong headed - would it even be effective? I think a GZ34 would take the lions share of a heavy load, until it failed.
In the scenario of loads over 250mA and valve rectification, dual rectifiers aren’t a new thing 
https://el34world.com/charts/Schematics/files/Selmer/Selmer_pa100.pdf