Ampeg PT wiring

[JoeCon]

Guys

I recently got an Ampeg PT I want to use in another build. It’s from a Gemini 1 from the 60’s.
I found a schematic and it shows the black and red/black are ac in.
The two reds are B+ to the rectifier.
The green and red/green are the heaters…
Problem is there is still an unused white wire…not on schematic.
Any ideas.
Thanks……

[R.G.]

Get out Mr. Ohmmeter. Resistance from white wire to all the others?? My guess is it may be a tap, perhaps CT on the high voltage, or a bias tap.

When you find out what other windings it connects to, switch to Mr. DMM and measure voltages. Carefully and safely...

Could also be a wire to an internal shield, intended to be grounded.

[sluckey]

Check for continuity between the white wire and all the other wires. Then tape off the white wire.

[JoeCon]

Thanks guys, I’ll check it out….
It was interesting not a word about it on the schematic….

[Stevem]

That PT was used in a whole slew of different model Ampeg amps.

That white wire should be the filament center tap.
On some models it went right to ground, or it went to a hum balance pot, or it got fed DC to bias up the filaments when the amp used a cathode biased output stage.
The latter that I posted here is where I would hook it to, that is to say the tube side of the cathode cap and resistor.

[Stevem]

That PT was used in a whole slew of different model Ampeg amps.

That white wire should be the filament center tap.
On some models it went right to ground, or it went to a hum balance pot, or it got fed DC to bias up the filaments when the amp used a cathode biased output stage.
The latter that I posted here is where I would hook it to, that is to say the tube side of the cathode cap and resistor.

[Stevem]

That PT was used in a whole slew of different model Ampeg amps.

That white wire should be the filament center tap.
On some models it went right to ground, or it went to a hum balance pot, or it got fed DC to bias up the filaments when the amp used a cathode biased output stage.
The latter that I posted here is where I would hook it to, that is to say the tube side of the cathode cap and resistor.

[Stevem]

The response of this site and the things that it does has been so screwed up over the last 2 days!

What’s up?

[JoeCon]

Here’s the schematic picture I’ve got…no white

IMG_5212.png

[Stevem]

Then simply don’t use that white wire, just shrink tube it off and roll it up in a loop and cable tie it.

[didit]

Hello --

If this transformer has an electrostatic copper foil wrap, check for continuity to that white wire.

Best ..

[Stevem]

So you can put this to bed here’s what that white wire is on a new replacement PT.

[sluckey]

That PT is not a replacement for his PT. His original PT has a much lower HV winding without a center tap and is meant for a full wave bridge rectifier. This "replacement" is for a conventional full wave rectifier. However, the white wire may still be a center tap for the heater. But since joe has not reported any continuity/resistance readings as requested, we still don't know any more than we did from the git-go.

[Stevem]

Yes, and he still needs to check, but I posted this because I have used this PT from Hammond in a echo twin and one sold by Fliptops for a replacement in the same model as his PT he is questioning.

In both cases of replacement PT’s the white was the heater CT.