Could I ask a question about power transformers?

[deuce42]

Hello guys

I am wondering if someone could help me understand whether I can link power transformer secondaries together for my circuit?

I'd like to make a single channel AB763 Super Reverb circuit but with a solid state rectifier and no tremolo circuit. The transformer I have has the following secondary taps:

OUTPUT - HT (OUTPUT) - 0 - 235VAC @ 250mA (NO CT)
HT (PREAMP) - 0 -125VAC @ 100mA (NO CT)
BIAS TAP - 0 - 50VAC @ 100mA (NO CT)
HEATER TAP - 0 - 6.3VAC @ 2A (NO CT)
HEATER TAP - 0 - 6.3VAC @ 2A (WITH CT)

Accordingly I'm trying to understand whether I can connect the two HT taps in series to make them 360v combined and connect the two 6.3v's in parallel to get 4A of current in the heaters.

I am also guessing I'll need to change the full wave/half wave rectification as a super reverb usually needs a centre tap in the 360v and I only have a single tap.

I know these are very rudimentary questions but could you guys help me understand if this is do-able?

Thanks very much.

[martin manning]

No problem paralleling the two heater windings, but since the 125VAC winding is rated at 100mA, that will set the current limit if you connect it in series with the 235VAC winding and that's not enough for what you want to do. If you use the 235VAC winding by itself, you'll be about 100V low on the DC side.

[deuce42]

Oh I see. How about if I used the 235v with some sort of voltage doubler components. Is that possible to allow enough HT current and voltage?

[martin manning]

Doubling the voltage will make it way too high- 235 x 1.414 x 2 = 665V.

[deuce42]

Ok I see. Time to find another xformer.

Thanks for your assistance Martin Manning.

[jon]

Hold the phone. You can voltage double the 235v and run the screens at a much lower voltage. Look at a univox u-1236 for how to wire the rectifier and filters.

[deuce42]

Oh thanks for your help. So do you mean change the screen resistor values? Ie 1k as in the Univox Schematic I just downloaded or am I missing something in your point?

[martin manning]

Hold the phone. You can voltage double the 235v and run the screens at a much lower voltage. Look at a univox u-1236 for how to wire the rectifier and filters.

This PT matches the U-1236 quite well voltage-wise, but not in current. That would hardly make a Super Reverb, though, would it?

[ToneMerc]

Hold the phone. You can voltage double the 235v and run the screens at a much lower voltage. Look at a univox u-1236 for how to wire the rectifier and filters.

This PT matches the U-1236 quite well voltage-wise, but not in current. That would hardly make a Super Reverb, though, would it?

Yes Martin you are correct. For a doubler configuration the HT winding current of the OP's power transformer is lacking big time.


TM

[cxx]

I built one with low voltages. Adjusted the dropping string for the preamp. Kind of like power scaling only permanent. It does behave differently and crunches up more and earlier. Quieter too. You can always replace the transformer later.