Where to ground heaters virtual center tap?

[brewdude]

In an attempt to eliminate some noise in my Brown Note D'Lite, I am considering lifting the PT's heater winding center tap and installing a virtual center tap with a hum balance pot.

I have seen the virtal center tap grounded to the power tube's cathode on cathode biased amps to elevate the ground. Where's the best place for a virtual center tap ground on a fixed bias power amp?

Is there a common way to elevate the ground? Is it necessary to elivate the ground?

[Structo]

You would ground the two 100 ohm resistors to, chassis ground.

But, I have to say as being an owner of a D'lite that you should not have to.

Did you build this from a kit?

If you properly twisted the heater wires and have run them overhead of the sockets and have kept all signal carrying wires away from them, the hum should be very low. Not enough to worry about.

I would check your lead dress and also try different tubes.
If the power tubes are too far mismatched that can cause hum as well as a faulty preamp tube.

Can you post some gut shots of your amp?

[stoo]

Ya that mod is for 60hz hum only and doesn't do anything for "noise".
Stew

[brewdude]

Thanks for the replies.

Yes, I did build it from a kit, and I have taken great care with the lead dress and all the ac wires are twisted neat and tight. Perhaps the noise I am chasing is completely un related. Sometimes it seems noiseier than others. My house poorly grounded, if at all, and I do have some flourescent lights and some dimmer switches. I need to step out of my bubble and take it somewhere else for a test drive.

Thanks.

[Structo]

Yes, bad house wiring can give you grief.

I would suggest you try it at a different location before tweaking.

I notice on my amp I get a bit more hum on the OD channel.
Not bad but more than the clean.

One thing I noticed when I was first playing, if the wire from the standby switch to the board passes too close to any of the AC wires in the power supply it can pick up some hum. So isolate that.

I ended up installing a choke and reconfiguring the standby so the first large filter caps get charged at power up but the rest not until the standby is thrown to play position.

[AJD]

Hey Brewdude,
Fluorescent lights and dimmers can both cause a surprising amount of havoc. I would recommend first testing your outlet to see that it is properly grounded (there is a small inexpensive plug-in device that you can get at HomeDepot for this). Then I would turn off all of your lights and dimmers and then try the amp again. You may notice a big difference. I remember spending hours combing over the circuitry of my first build looking for the source of noise (it wasn't much noise, but I wanted No noise). In the end it turns out that my apartment was poorly grounded and a light dimmer switch was also inducing noise. At my new place the same amp is quite as can be.

[Structo]

Also note that even under the best conditions, if you are standing near the amp it will increase the hum. Even with a humbucker equipped guitar.

Try standing further away and then turn your body for the least amount of hum.

[brewdude]

Thanks, I will not get much chance to get back to it for a week or so, but I am encouraged and believe that I might be making a mountain out this mole hill.