Wiring my power transformers with 3 heater windings

[hembrook]

Howdy

I got the Trafomatic transformers. Nice work, if not aesthetically the best. Simple, unadorned by covers. I'll add pics later.

On the power transformer, I have 3 6.3V heater windings. The GSG board has inputs for 2. Here is my thought:

Wire one winding to the normal left and right terminal blocks on the board. This lets me power the 6A5Gs with DC power, and all is good.

When I install the tube sockets to the board, lift the legs on each socket that are for heaters: Pins 2 & 7 for the 6AX5 and 7 & 8 for the 6SL7. Fly those legs ABOVE the board, and wire them directly to the third heater winding. Insulate where proper to keep the sockets from touching their heater voltage pads on the board. This eliminates cutting traces, and allows me to keep the DC circuits for the power tube heaters.

It would be nice to run the 6SL7 on DC, tho, so maybe I need to look into making a small rectifier for that.

Obviously, the 6AX5GT can't run on DC heaters...

Does this make sense?

Thanks,

Robert
Mannheim

[Shannon Parks]

I like your idea, Robert, and see no problem with it. Ultimately, I'm not sure if you'd gain anything by not doing it the stock method. The neat thing about the stock method is that the filaments all get DC ground referenced through the 6B4 circuit - something else to consider.

[hembrook]

I ordered the tranny with a spare winding so that each power tube would have its own winding. Seemed like a good idea at the time.

I could tie the third winding off and leave it alone, I suppose.

On the other hand (OTOH) what do I lose by losing the DC ground reference? Will I get some DC offset between the 6SL7 and the 6B4G/6A5G? I guess the big-assed Orange Drops in the signal chain take care of that.

Lots of fun to experiment with...

[Shannon Parks]

Don't let me dissuade you from your method. You'll just want to DC reference the filament on the 6SL7, with either a resistive divider or just even grounding one side of the filament (ala Eico). The GSG method I use isn't anything special - indeed I wasn't sure it would work when I first came up with the circuit using the PA774 - but it works well. Yellow_Light_Colorz_PDT_06

[hembrook]

Since all 3 windings off the transformer for the filaments are 6.3V, I don't see a problem getting power to the filaments, but I am a bit confused by how to DC reference the 6SL7. Which end of the filament do I need to ground, and what is the best point on the board? I am worried I will get something out of phase and get 3 filament windings working against each other.

[Shannon Parks]

I don't see a problem getting power to the filaments, but I am a bit confused by how to DC reference the 6SL7. Which end of the filament do I need to ground, and what is the best point on the board.

Just connect the third filament circuit to the rectifier and 6SL7. Then get two 1k resistors (or any matched pair in the ballpark) and attach either end to that 6.VAC circuit with the divider between the resistors attached to the signal ground around the 6SL7. I wouldn't worry about the phases for now.

[hembrook]

Just connect the third filament circuit to the rectifier and 6SL7. Then get two 1k resistors (or any matched pair in the ballpark) and attach either end to that 6.VAC circuit with the divider between the resistors attached to the signal ground around the 6SL7. I wouldn't worry about the phases for now.

Lets assume I fly the leads in from the 6.3v winding to the heater on the 6AX5 first, then the 6SL7:

So from, say the 6SL7 socket, attach to the heater pin 7 a 1kohm resistor, then attach another one to the pin 8, then tie their ends together and attach that to the signal ground somewhere, such as J1 Pin 2? Or did I get that wrong?

Thanks!

Robert

[Shannon Parks]

You got it, Robert.

[hembrook]

You got it, Robert.

Groovy. Nice to know I can still think on my feet (with enough goading).

I suppose this would come in handy for anyone elase who calls up Trafomatic and asks for the "Robert Hembrook Special" Yellow_Light_Colorz_PDT_16

[hembrook]

I was just planning on using standard Rat Shack 1/4W resistors. I don't think it is a critical application, but let me know if I am going to be dissipating current thru this (its essentially a voltage doubler, right?) Do I need to worry?

Thanks!

[Shannon Parks]

I was just planning on using standard Rat Shack 1/4W resistors. I don't think it is a critical application, but let me know if I am going to be dissipating current thru this (its essentially a voltage doubler, right?) Do I need to worry?

They'll be fine. Each resistor will have a 3.15VAC drop to ground across them. So (3.15*3.15)/1000= .01W or 10 milliwatts.

[hembrook]

They'll be fine. Each resistor will have a 3.15VAC drop to ground across them. So (3.15*3.15)/1000= .01W or 10 milliwatts.

Ain't Ohm's Law great! I thought as much, but I wanted to be sure I wasn't missing something like turn on surge or the like.

Rock on. Off to make some more holes in diamond plate.