Harmony H304A Circuit question

[davohilts]

Hello,
I'm rebuilding a 403A and am amazed at what a simple circuit it is. I have a couple of basic questions.
1. The 6C4 tube (V1) shows on the schematic as having the cathode (p7) grounded. The amp I have has a 4.7K resistor going from the cathode to ground. It is an old carbon comp resistor had make a nice white noise sound that I'm not real happy with. I can pull it out of the circuit and just ground the cathode and reduce the white sound but I'm wondering if anyone can explain the use of a resistor in this capacity?
2. The existing and what appears to be original cap can is a 40x20x20x400v. the schematic shows a 4x20x400v cap array and what i'm guessing is that the C7&8 are tied in parallel to make the 40mfd cap. Does this seem right?
Thanks for any insight.
Here is a schematic.

[Jazz P Bass]

The cathode resistor allows the grid to be self biased.
I would leave the 4.7K in. (replacing it with a new one)
I think that grounded cathode is a mistake in the drawing.

[davohilts]

The cathode resistor allows the grid to be self biased.
I would leave the 4.7K in. (replacing it with a new one)
I think that grounded cathode is a mistake in the drawing.

Yes, the schematic seemed a little basic. The amp I'm working on also has a cap bypassing the 250 ohm cathode resistor (r11) on the 6v6 tube which I'm replacing with a fresh one (47ufx25v). I'm
wondering if it might be a good idea to bypass the cathode resistor on the 6C4 tube?

[sgelectric]

Is C1 (.003) present in your amplifier?

[davohilts]

Is C1 (.003) present in your amplifier?

yes, it was an old ceramic disc cap, i replaced it with a new .003 orange drop.

[sgelectric]

The schematic seems to have an older style of tube biasing sometimes referred to as "grid leak" or "contact bias". This is consistent with the grounded cathode and the input capacitor.
The fact that you have a cathode resistor implies that someone tried to convert it to "self bias" as Jazz P Bass mentioned.If this is in fact the case, you should be able to remove C1 and add a cathode cap if you choose to.
As I am no authority in these matters, I will refer you to a link that talks about a similar conversion.Pay particular attention to jrfrond's reply #4.


http://music-electronics-forum.com/t8864/

http://www.webphix.com/schematic%20h...nivox_u45b.pdf

Hope this is useful to you.

SG

[davohilts]

Thanks for the help, I'll check it out.
Dave