Practical questions on DC heater circuit

[Ken Moon]

Can a humdinger be used at the same time as elevating the heater center tap? Or, when using a humdinger, does the heater center tap wire need to be taped off?

It looks like the humdinger is basically the same as using two 100-ohm resistors to form an "artificial center-tap", but the 100-ohm resistors can be varied in value.

If this is so, is there something about the single humdinger pot that is better than using two separate 100-ohm pots?

[stevehoover]

I usually have pretty quiet heaters but on a Normal channel 6G6B Bassman build with a different power supply vendor I was having a lot of heater noise. Don't know if it is significant but transformer itself is a talker and has a lot of mechanical noise...even with no load...so...

I "de-elevated" my heaters by approximately -35 volts by connecting a lead from the output of my bias supply to the center tap of the heater windings.
It dropped the heater noise in the circuit way way down.

I guess it is an old trick and you do have to be careful of exceeding cathode voltages anytime you elevate or de-elevate where the circuit has a cathode follower in use. So far (2 months of use) no issues.

[Luthierwnc]

The second issue was a grounding problem. I researched a post on the Dumble Discussion and relocated the grounds for the internal loop off the bus bar and over to the power tube cathode lugs. Cleaned it up quite a bit. I won't be completely sure until I put the shields on the tubes and put it in the shielded cab away from all the fluorescents in the basement.

Thanks for all the ideas.

A while back I got a start on a hum/buzz sticky that attracted some attention. I'd still like a guitar amp maker's primer on practical methods of debugging these gizmos -- based on the equipment available to the reader. Nobody should quit their day job but a file on scope screens that identify ground loops, 120 vs 60hz hums, parasitics, lead-dress nightmares and the like. Someday. sh

[pops]

I have used a bridge rectifier on the heaters after the power tubes and then just like your power supply a resistor and cap for each tube to V1. Perfectly quiet and went on the tube sockets so room was not a problem.

[trobbins]

Can a humdinger be used at the same time as elevating the heater center tap?

Yes.

It looks like the humdinger is basically the same as using two 100-ohm resistors to form an "artificial center-tap", but the 100-ohm resistors can be varied in value.

If this is so, is there something about the single humdinger pot that is better than using two separate 100-ohm pots?

A single pot is simplest to deploy, with wiper going to the 0V or the elevated voltage node. Using two pots may lead to both pots being set at 'zero', which would short-circuit the heater winding.

In some situations the hum can be nulled/attenuated, whereas in other situations the pot provides no benefit. The hum can be from the valve used, just as much as wiring layout, and/or rectifier noise from the B+ supply. Hopefully one dominant form of hum ingress is identifiable, and hence a solution aimed for.