I've posted this question on ARF as well but for those of you here who don't visit there I'll post it here as well in case any of you have an answer.

I'm working on recapping this standard AA5, ( a Clarion C-100 ( made by Warwick)) ... and it's been re-worked already a lot in the past so I'm trying to piece it back together properly.

Someone has replaced the output transformer with what seems like a reasonable substitute and for the most part it's working nicely except for what seems like an excessive AC hum level.

I'll be checking lead dress and looking for tubes with problems that may be a cause.

Recently I've been successful in killing hum problems in AA5s that used to have a hum-buck tap on the original output transformer but where it's been replaced with one that doesn't have one. So in that case I've upped the filter-cap values or added a 3rd stage of filtering with great success.

So I can certainly do the same here as well, if need be.

But my question about this particular radio's schematic relates to the 10k resistor R9 from B+ to the cathode of the 50L6.

What is the design purpose of this? I haven't seen this employed before on other AA5s.

Is it there to help cancel some of the hum by feeding a small amount of B+ ripple into the cathode out of phase?

It doesn't seem to make any noticeable difference in this radio. As I clip it out or put it back in.

Any ideas?
http://www.nostalgiaair.org/Resources/228/M0023228.htm

:I've posted this question on ARF as well but for those of you here who don't visit there I'll post it here as well in case any of you have an answer.
:
:I'm working on recapping this standard AA5, ( a Clarion C-100 ( made by Warwick)) ... and it's been re-worked already a lot in the past so I'm trying to piece it back together properly.
:
:Someone has replaced the output transformer with what seems like a reasonable substitute and for the most part it's working nicely except for what seems like an excessive AC hum level.
:
:I'll be checking lead dress and looking for tubes with problems that may be a cause.
:
: Recently I've been successful in killing hum problems in AA5s that used to have a hum-buck tap on the original output transformer but where it's been replaced with one that doesn't have one. So in that case I've upped the filter-cap values or added a 3rd stage of filtering with great success.
:
: So I can certainly do the same here as well, if need be.
:
:But my question about this particular radio's schematic relates to the 10k resistor R9 from B+ to the cathode of the 50L6.
:
:What is the design purpose of this? I haven't seen this employed before on other AA5s.
:
:Is it there to help cancel some of the hum by feeding a small amount of B+ ripple into the cathode out of phase?
:
:It doesn't seem to make any noticeable difference in this radio. As I clip it out or put it back in.
:
:Any ideas?
:http://www.nostalgiaair.org/Resources/228/M0023228.htm

If you know you are working with a clean circuit, shut all the circuits off in your house one by one and see if you can clear your hum. I know you are thinking way deeper, talking about out of phase ripple and such, but maybe it's something more simple this time...Neal