Used wrong resistors but Champ amp sounds great should I change them?

[HansVG88]

I built a 5f1 champ type amp and because it had hum issues I used a twisted pair heater from the 6.3 volt PT (green) wires. There was no center tap from the PT so I wired in a "fake" CT with 2 resistors. The amp sounds great and the noise floor is very acceptable even at full volume.
I removed the chassis from the cab to install it into a improved version cab and I noticed that the CT resistors are 100K and I think they are supposed to be 100 ohm.
Like I said the amp sounds very good...but...am i doing harm to the tubes or PT or anything else? It has nos telefunken 12AX7 and nos tung-sol 6V6GT so I would hate to do anything that would harm them or shorten their lives.
This forum is the reason I was able to get through this (my first) build and I know you guys have the answers.
Thanks

[Tom Phillips]

You are not doing any "harm" but the virtual center tap would be more effective if you switch to 100 Ohm resistors.

This is an opportunity to do a little experimentation if you are interested.
1) Disconnect the two 100k resistors from ground. Does hum level increase. If so they were performing the hum reduction function.
2) Replace the 100k values with 100 Ohm and re-connect the ground. Did that lower the hum level vs. the 100k? If so that would demonstrate that the lower value works better. The 100 Ohm is not a magic value. I have seen up to 500 Ohm specified on old schematics via the use of a 1000 Ohm hum balance pot.
3) Another option is to connect the two resistors' common point to the cathode of the power tubes thus elevating the heaters. This may give you an even lower hum level.

Let us know what you discover.

Regards,
Tom

[HansVG88]

Thanks for the reply Tom. I went to a guitar show today but I will play around with the resistors and virtual center tap sometime this week and let you know how it goes.

Hans

[HansVG88]

I removed the 100k resistors and the noise increased a bit. I replaced them with 100 ohm resistors with the common end at the power tube cathode and the amp is dead quiet and still sounds great!

[Shea]

Weber VST sells a 200 ohm, 2 watt pot with a screwdriver slot which makes a good hum balance pot.

[electrochronic]

With regards to your tubes. I'm running vintage black plates and want to be careful how they are being fed by the PT.

A. acceptable bias on the 6v6 40-45ma - check cathode bias resistor. I installed a 1ohm in series before the 470 ohm. this way I can check the vdc over the 1 ohm 2w resistor. its millivolt measurement will convert directly to milliamps. this gives you the ability to check it at anytime.

B. heater voltage should not be higher than 6.3vac and not below 5.9vac
I installed a 1 ohm 1 watt resistor in line with one of the heater wires at the
pilot lamp. All the heater voltages (wired series parallel) from the 6v6 to the 12ax7 read 5.99 vac.This slightly lower heater voltage will run the heaters with less stress and will prevent shortened tube life. Over voltage to heaters ( above 6.3vac ) burns them up faster. same applies with the 5 vac on the 5y3 rectifier tube.