power supply design for dumblator w/this transformer -Q

[Pete]

I have a 220-0-220V @20ma. with 6.3V @1.5A that I know would work for a dumblator and need help with the PS.
I've seen a couple of schems recently posted but they are using a 0-135v (with doubler) or Fender Reverb iron (Thanks, to Funk & heisthl for posting these) and I'm not sure how to alter them for use with my Xformer.

I don't know much about power supply design (guitar player with 40 years soldering experience, a few amp builds from scratch & schems, but short on all the theory & technical).
Any suggestions or links to info appreciated.

[Funkalicousgroove]

wire it full wave, you'll have low b+ but it should function, perhaps use smaller resistors in the dropping string to compensate-

[Funkalicousgroove]

wire it full wave, you'll have low b+ but it should function, perhaps use smaller resistors in the dropping string to compensate-

[Pete]

Thanks Funk,
I have attached a drawing of what I used for the power supply. It works though not super quiet.
I just noticed I used 47k where I think I wanted 470K, I'll try changing those (may give a few more volts). Choke is Princeton/Deluxe replacement type. Not sure if I should be using anything different for dropping Rs. Voltage is in the ballpark I guess.
I welcome any comments on changes/improvements from anyone, thanks.
** EDIT** - I just checked, they are 470K. Sorry for the confusion, drawing fixed**

wire it full wave, you'll have low b+ but it should function, perhaps use smaller resistors in the dropping string to compensate-

[Funkalicousgroove]

part of your hum is probably from the small resistors, those need to be 270K-330K, good call on the choke!

[Pete]

Thanks, I just checked again after I posted and I do have 470K in there. (I have edited that post). I may try something in the range you stated but don't have anything on hand right now. Maybe try a different 12AX7 to see if it gets any quieter.

part of your hum is probably from the small resistors, those need to be 270K-330K, good call on the choke!

[odourboy]

Make sure that CT on the heater winding is connected to ground, or alternatively, run a 100 ohm resistor off each heater tap to ground. If that's missing, she'll hum big time.

[Pete]

Thanks, I tried both methods, CT not connected using 100 ohm resistors and connected CT without resistors. Surprisingly to me, I found the latter to be a little quieter.

Make sure that CT on the heater winding is connected to ground, or alternatively, run a 100 ohm resistor off each heater tap to ground. If that's missing, she'll hum big time.

[Funkalicousgroove]

you can also use like a 50K pot and a couple of 75K(ish) resistors, connect the wiper to ground, and put the resistors on the outside lugs and connect the other ends to each heater tap respectively. Turn the pot to where it is quietest- Like the old silverface hum balance, CBS wasn't all bad

[Pete]

Thanks a million Funk,
I read your comment and the light bulb went on ... I remembered I have one of those "Hum Balance" pots in the parts box somewhere ... well, I found it. No doubt it came out of an old silverface somewhere.
Looks like a bias pot but 100 ohm. Put it in, (disconnect CT on 6v winding) dialed out much of the hum. Then I changed the tube and even lost a bit more hum. Just had one of those hours of testing (playing) that turns into two or three before you know it.
Can one expect these things to be dead quiet?
I'm still getting a little of that gain kind of sound. I know you would hear stuff if you crank it enough, but I can hear it at about unity.

you can also use like a 50K pot and a couple of 75K(ish) resistors, connect the wiper to ground, and put the resistors on the outside lugs and connect the other ends to each heater tap respectively. Turn the pot to where it is quietest- Like the old silverface hum balance, CBS wasn't all bad

[Funkalicousgroove]

You can get them pretty darn quiet, but anything with tubes makes a little noise.

[drz400]

Dont forget that you need to shield the preamp tube and get it as far away as possible from the Power transformer