Grounding filament supply with voltage doubler hum

[dobrota]

I've built mini amp with tube PCL86. There is 1/2 12AX7 triode and pentode similar EL84 inside this tube. A little problem is filament voltage because it's 13.3V / 300mA, not usually 6.3V
So I made filament as DC voltage using voltage doubler from 6.3V winding (2x diode, 2x 1000uF capacitor, 15Ohm resistor and next 2200uF capacitor with grounded - point ). All ground method is - from anode voltage rectifier, ground from pentode cathode RC, - from last filament capacitor connected together in one point, then next wire from this point to triode cathode RC, last anode voltage capacitor connect near input and input jack grounded to chassis. I've used it this way before in other amp and it works well (only filament was AC with two 100 Ohm resistors and grounded common point)
Heater voltage value is OK, all works but there's some strange hum, not 60Hz hum but rectifier like hum in signal.
I don't know if it's because of wrong filament groud method or capacitors have to be bigger or some other uknown reason.
I thank You very much for Your advices

[Leo_Gnardo]

I don't know if it's because of wrong filament groud method or capacitors have to be bigger or some other unknown reason.

I'd go with bigger capacitors. Also I'd avoid cheap 1n4001 1 amp rectifiers in this situation, instead use next size up 3A 1N5400 or UF5400 rectifiers. 1 amp rects would be under a heckuva strain especially on startup. 1N or UF5400 = 50 PIV should be enough in this circuit.

[g1]

I'd go with bigger capacitors.

Yep. Lot's of modern stuff has DC heater filtering in the thousands or even tens of thousands of uF.

[Chuck H]

Your ground scheme sounds like you may have the filaments and power supply grounded in two places? Make sure you don't have more than one ground for any circuit. And make sure the power supply or filament supply isn't sharing any ground leads with the preamp grounds. For that matter, I have better luck NOT grounding anything related to the power supply or filament circuit near the input UNLESS ALL GROUND LEADS ARE RUN INDEPENDENTLY ON A SINGLE LEAD TO A SINGLE POINT with no sharing.

Just because it's worked before doesn't mean there may not be slight requirement differences now. For one thing, an AC circuit with a false CT is somewhat self cancelling. his wouldn't be the case now. I would definitely recheck for potential ground loops or shared leads and probably move any power supply or filament grounds to the other end of the chassis.

Oh... And increase capacitance as mentioned

[dobrota]

Thanks for your reply. No, there aren't two ground places for filament and power supply in my circuit. I have only one common point for connect between minus point (ground) from PSU rectifier, minus from last capacitor of filament voltage doubler and lead from ground / cathode RC of power amp pentode tube. Preamp ground line than goes from pentode cathode ground. But question is, if ground of minus of voltage doubler capacitor is OK, if one point from filament winding isn't right / better because it's some "virtual" center of heater circuit / voltage doubler. I have to try it.

[Chuck H]

A schematic might help. Sometimes the more eyes (brains) you have on something, the better.

If it's a loud hum it could also be a wiring error. Maybe a filter placed across the wrong point of a ground connection that was overlooked. Not to imply any failings of skill at all. It happens.

Also, if this is a new build, NEVER AUTOMATICALLY TRUST THE TUBES!!! Even if they're new. I've had many hummy or otherwise noisy tubes new right out of the box. I spent hours chasing a hum on a new build (with new tubes). I assumed I must have made a mistake or maybe a filter was bad. I had to rule out everything before the light came on and I "fixed" it with a different preamp tube.

[J M Fahey]

So I made filament as DC voltage using voltage doubler from 6.3V winding (2x diode, 2x 1000uF capacitor, 15Ohm resistor and next 2200uF capacitor with grounded - point ). All ground method is - from anode voltage rectifier, ground from pentode cathode RC, - from last filament capacitor connected together in one point, then next wire from this point to triode cathode RC, last anode voltage capacitor connect near input and input jack grounded to chassis.

Oh my God!!!, my head

please just post the d*mn schematic !!!!!!!