Rectifier safety diodes question

[mresistor]

I have a 5F6a Hoffman boarded clone that takes the bias voltage source from one of the AC leads to the rectifier, say pin 6.  I'd like to add safety diodes to the rectifier socket to prevent damage to the PT from a rectifier flash-over, which seems to happen with the new gen 5AR4 rectifiers from time to time.
It doesn't seem like a good idea to install them in series with the AC leads before that tap off to the bias circuit. I saw recently that one could place the diodes from pins 4 & 6 to pin 8. However I cannot for the life of me find that post here on the forum where I saw that.


Will this be OK to install the diodes from pins 4 & 6 to pin 8? This will be after the bias tap.


thank you

[92Volts]

Found a thread elsewhere about this: http://dynacotubeaudio.forumotion.com/t1006-tube-rectifier-diode-mod

Electrically you're just putting the diodes in series with the tube, one for each (vacuum-tube-based) diode of the tube itself.

Unused pins of the tube can act as attachment points for the transformer windings and one end of each diode. They give an example there but there's at least 1 more unused pin of a 5AR4 you could use to do it differently.

[mresistor]

Thank you 92 but I don't think you are understanding my question. I have a tap on pin 6 that is taking the AC voltage at that point and taking it to the bias circuit on the Hoffman 5F6a turret board.
I am concerned about that tap and the effect of putting a diode in front of it.


Can anyone point me to the recent post on this forum where this was discussed? It would be appreciated immensely,  I'll buy you a beer....

[sluckey]

This is not the mod you want to do. What you propose just puts the diodes in PARALLEL with the tube diodes. Then you would remove the tube so that you have a SS rectifier mounted on the tube socket. Not what you want.

Do it exactly like the mod in the link 92Volts posted. You also need to move the bias wire from pin 6 to pin 7.

[sluckey]

This is probably what you are thinking about, but this ain't what you want.

Reply #18...

http://el34world.com/Forum/index.php?topic=18231.msg239385#msg239385

[mresistor]

Thank you both - I am sorry Steve I didn't see your first post and I didn't notice in the link that 92 posted that the author was using pin 7 instead of pin 5 - and I'm also kicking myself for not thinking of that ..      


Fantastic   - many thanks to sluckey and 92      much appreciated