Simulated center tap on heaters?

[888guitars]

Has anyone used a simulated center tap on the heaters? I have been building a champ with 2 preamp tubes and its pretty noisy. Was told to try a simulated center tap. I guess it balances the ground?

[nickb]

The idea is that it minimises the volatge swing between the heater and the cathode and thus minimises the unwanted (hum) current. Worth trying. It's also importmant that all heater wiring is neat, twisted togther and kept away from signal wires.

[JHow]

I think many people use this technique. It only costs you the price of two 1/2W 100R resistors, so not much at stake here. Note: If your transformer has a CT on the heater line, you can't do this trick. Many people will hang the two 100R res. off the pilot lamp, grounding them to the chassis on a PT bolt. Also, you can do the "DC elevated" version and instead of grounding to chassis, take the ends of the two resistors to the cathode pin of your power tube. If you are careful, you can actually fold the resistors on the bottom of the power tube socket and make these connections directly to the pins.

Hoffman has a de3scription here, under "heater hookup":

Common hookup info

[jrfrond]

I think many people use this technique. It only costs you the price of two 1/2W 100R resistors, so not much at stake here. Note: If your transformer has a CT on the heater line, you can't do this trick.

Well you can, you just don't use the center-tap. If you want to get really picky about it, you can install a 100ohm hum-balance pot to find the exact null for the hum. This is particularly important on SE amps like this, because residual induced hum doesn't cancel in the OT like it does in PP designs.

For heater wiring, the tighter you twist them, the better. Tighter twisting increases the humbucking effect. Take two equal lengths of heater wire (a couple of feet long), clamp one end of them in a vise, and chuck the other in your cordless drill. Then twist 'em on low speed. Cut the lengths you need from this master pair and your all set.

[mooreamps]

Yes, for filament windings that do not provide a center tap. But, I wonder if others using the Simulated center tap on the H.V. windings ??


-g

[jimboyogi]

Yes, I have done this on 2 champ/princeton builds now, and both seem to have VERY low heater hum coming through the speaker.
I put the 2 * 100R 1/2W resistors on the output tube socket, from the cathode (octal pin 8) i run one to pin 2, and one to pin 7, the two heater pins. This sorts out both the artificial heater centre tap, and the heater DC elevation, both at the same time. Then just run your regular twisted pair of heater wires on from the output tube to the preamp tube/s.