Individual Cathode Bias Resistors and DC elevated heaters

[trobbins]

Are you using a humdinger type connection to the bypassed cathode?

[potatofarmer]

If you have room on the chassis you could always add a separate heater transformer for the first preamp tube. Run it at 12V, elevated and humdinger'd, heck DC if you really want. Probably like using a sledgehammer to swat flies, but I thought I'd mention it.

Painful though it may be, it's definitely a better idea to try to improve the lead dress before you worry about anything else.

[brilliantblue]

Thanks for the additional responses.

The hum isn't a huge concern. I'm only considering affecting it still due to not having completed the cabinet - so the amp is still "open".
I'm not going to use a separate transformer due to no chassis room.

I pulled the "artificial center tap" from the amp altogether due to the unique shared heater/High Voltage center tap .

Is it possible to affect the balance using a hum pot if with the original center tap still connected? what happens if i try that?

I suppose i could bypass the first stage cathode with a cap high enough to leave the hum behind. But this amp, essentially a 6g3, has more than enough gain already so had pulled the pre-bypass caps to tame it a bit.

Thanks
JEff

[Jazz P Bass]

I pulled the "artificial center tap" from the amp altogether due to the unique shared heater/High Voltage center tap .

Is it possible to affect the balance using a hum pot if with the original center tap still connected? what happens if i try that?

I think it is 'one or the other'.

[trobbins]

I think it is 'one or the other'.

I agree. And just to comment that it has to be one of them - you can't leave the heater supply floating.

[eschertron]

I suppose i could bypass the first stage cathode with a cap high enough to leave the hum behind. But this amp, essentially a 6g3, has more than enough gain already so had pulled the pre-bypass caps to tame it a bit.

Thanks
JEff

Gain and hum can both be managed, various ways. If fully bypassing the 1st stage cathode resistor gets you the hum reduction that you want, then reducing the gain at (or after) the anode of that stage will grant additional hum reduction
Something I've seen but haven't tried is splitting the anode resistor into two, and tapping the output from between. This can give you some gain reduction control without a lot of mess.

[brilliantblue]

Gain and hum can both be managed, various ways. If fully bypassing the 1st stage cathode resistor gets you the hum reduction that you want, then reducing the gain at (or after) the anode of that stage will grant additional hum reduction
Something I've seen but haven't tried is splitting the anode resistor into two, and tapping the output from between. This can give you some gain reduction control without a lot of mess.

An interesting idea!
I'd not disclosed before that this heater string was running a bit high at 6.6v - I lowered it with a .15 resistor to 6.3v. Then I replaced the individual 22uf cathode bypass caps with 10uf caps. Those changes further reduced apparent hum. I'm pretty satisfied now. I brought the 2nd stage cathode resistor up to 3.5k (from 1.5k) to see if it would clean up the sound any further. It seemed to help. I had mixed emotions at the result - glad to arrive at an amp to meet my friend's tastes, sad take it away from my own tastes!

Thanks again for all the help!
Jeff