Series/Parallel Heater wiring

[beasleybodyshop]

Question:

I have a transformer with a 3.15v heater tap, is there an effective way to use this so I get 6vAC on both heater lugs of my preamp/power tubes? apparently the 3v isnt enough to light up my indicator light either

[Stevem]

You would have to convert that 3.15 vac to dc, and that dc supply would have to be a voltage doubling type to get you over the needed 6.1 volts.

When you use such a power supply you end up with half the amount of current that you started with, so the transformer needs to start off with twice your current needs of your total number of tubes powered.
Do you know the current rating of that PT?

[beasleybodyshop]

heater tap specs at 4 amps.

so in essence, i need a bridge rectifier and a voltage doubling circuit in series with the heaters?

[tictac]

3.15v centertap... sounds like you've got a 6.3V filament transformer with a centertap.... i.e. 3.15V per each side of the CT (aka 3.15-0-3.15)

have you powered it up and measured across the two non-centertap leads?

TT

[beasleybodyshop]

No center tap. It should have one....I received a schematic from Mercury Magnetics (it has one of their PT's in it.) It shows one but it doesn't have one.

[Phil_S]

3.15-0 is a weird voltage. I suspect there is a broken lead that can be repaired. If MM gave you a diagram and you don't see the lead, pursue it with them. They will re-lead it for not very much money if you don't feel comfortable doing it yourself.

[beasleybodyshop]

Sorry, i meant to say that both leads are 3.15v, with no centertap.

[NickC]

Sorry, i meant to say that both leads are 3.15v, with no centertap.

Seems like that tube-heater transformer should supply 6.3V with an artificial center tap?

[beasleybodyshop]

Sorry, i meant to say that both leads are 3.15v, with no centertap.

Seems like that tube-heater transformer should supply 6.3V with an artificial center tap?

Nick, this is for my Sovtek MIG50 - did yours have a center tap for the heater?

[NickC]

Sorry, i meant to say that both leads are 3.15v, with no centertap.

Seems like that tube-heater transformer should supply 6.3V with an artificial center tap?

Nick, this is for my Sovtek MIG50 - did yours have a center tap for the heater?

I believe so, but I'll have to confirm tonight after work. I used a replacement PT from Mercury Magnetics, made for modern 120V wall voltage. The original PT was delivering more than 6.3V to the preamp tubes heaters.

I do remember there are separate heater supplies for the noval and octal tubes, with the power tubes getting more voltage than the usual 6.3V. Those two wires are much heavier gauge. They are the heavy gauge brown wires on the original PT secondary.

[beasleybodyshop]

Yeah mine is a MM replacement too. I noticed the brown heater wires gave odd voltages - one wire was 18V, the other was 24V! it was hooked up that way and boy those tubes were glowing reeeeally bright I figured 4 amp was enough for the whole gamut, so i just used the one heater winding.

[Phil_S]

Question:
I have a transformer with a 3.15v heater tap, is there an effective way to use this so I get 6vAC on both heater lugs of my preamp/power tubes? apparently the 3v isnt enough to light up my indicator light either

So, your question is misunderstood...you have 6.3V, and you want 12.6V?

I'm not really clear about your PT. Did you say there are two 6.3V windings and you only used one? If so, you can run the two windings in series. This will give you 12.6V (6.3V on each outer leg) and 6.3V from either outer leg to the splice (CT) for the two windings. Make sure the windings are in phase, otherwise they are bucking each other to 0V. If are running mixed voltage, I don't know what you do about an artificial CT tor real CT for reducing hum.

It strikes me that you can ground the CT you create to get 12.6. Then just pair up the 6.3V tubes for series/parallel wiring so they all work with 12.6.

[NickC]

Here's the Mercury PT secondary wire code info:

Red 0V
Red 453V ..... B+

Black 0V
Green/Yellow 67V Bias Supply

Green
White 6.3V Filament heaters (9-pin preamp tubes)
Green


Brown 0V
Brown 7.3V Power Tube heaters

The 9-pin novel tube heater supply has the white wire as the center tap (grounded). The green wires go to the appropriate tube heater pins.

The brown wires provide 7.3V for the power tubes, with no center tap. Phase Inverter tube also gets the higher 7.3V heater supply.


Hope this helps

[Phil_S]

Nick,
What's up with 7.3? That's not a typo, seven point three...you typed it more than once.
Phil

[renshen1957]

Question:

I have a transformer with a 3.15v heater tap, is there an effective way to use this so I get 6vAC on both heater lugs of my preamp/power tubes? apparently the 3v isnt enough to light up my indicator light either

Hi

Why not a 6ax7 tube for the preamp? We use 12AX7 at the same way wired for 6.3 V, why not use parallel heaters for 6ax7. Might also work for the 6N2 Chinese tubes and the Rusky equivalent.

Just a thought

Best regards,

Steve