Seeking spec sheet for 125P1A power transformer out of a 1964 Fender Princeton

[PLX]

Searched all over with no luck.

 


Thank you !

[Blind Lemon]

8K primary/ 8ohm sec

[sluckey]

8K primary/ 8ohm sec

He's looking for a POWER TRANSFORMER spec sheet.   

[PLX]

Yes. It's the tremolo version.

[sluckey]

What's the whole story?

[PLX]

What's the whole story?

Schematic shows B+ of 315V, but I'm measuring over 400V

[tubeswell]

Going by the schematic for the 64 Princeton (attached), I'd say:

HT 340-0-340VAC @ 100mA
Heater 6.3VAC @ 4A (CT)
Rectifier 5VAC @ 4A

(Close enough to the 80W on the tube sheet)


NB: PT on 64 Princeton is 125P1B (The 6G2 was earlier)

[PLX]

At a guess I'd say


HT 340-0-340VAC @ 100mA
Heater 6.3VAC @ 4A (CT)
Rectifier 5VAC @ 4A


(Close enough to the 80W on the tube sheet)

That's a different transformer and different circuit than this amp.

This is the 6G2 with the 125P1A power transformer.

Wondering if I were to replace the 5Y3 rectifier tube with a solid-state bridge rectifier if I could lower that B+ ?

[tubeswell]

At a guess I'd say


HT 340-0-340VAC @ 100mA
Heater 6.3VAC @ 4A (CT)
Rectifier 5VAC @ 4A


(Close enough to the 80W on the tube sheet)

That's a different transformer and different circuit than this amp.

This is the 6G2 with the 125P1A power transformer.

Wondering if I were to replace the 5Y3 rectifier tube with a solid-state bridge rectifier if I could lower that B+ ?

Yes but you said 64 Princeton :-)


A SS diode rectifier will increase B+ more than a 5Y3

[PLX]

At a guess I'd say


HT 340-0-340VAC @ 100mA
Heater 6.3VAC @ 4A (CT)
Rectifier 5VAC @ 4A


(Close enough to the 80W on the tube sheet)

That's a different transformer and different circuit than this amp.

This is the 6G2 with the 125P1A power transformer.

Wondering if I were to replace the 5Y3 rectifier tube with a solid-state bridge rectifier if I could lower that B+ ?

Yes but you said 64 Princeton :-)


A SS diode rectifier will increase B+ more than a 5Y3

The date codes show May 1964 production.

I did have a SS rectifier in here at one point. Can't find my notes on that, but my B+ wasn't over 400V.

I put in an NOS Sylvania 5Y3 and was surprised to see that high of a B+

[tubeswell]

If you're gunning for a 6G2, it's more like a 5E3 PT, but with 290-0-290 or 300-0-300 HT winding

[tubeswell]

The date codes show May 1964 production.

I did have a SS rectifier in here at one point. Can't find my notes on that, but my B+ wasn't over 400V.

I put in an NOS Sylvania 5Y3 and was surprised to see that high of a B+

Then it'll be a late 6G2 and all bets are off as to what Fender put in there. It was probably different from what was out into earlier 6G2s, because things were changing all the time. Try a 5E3 PT (325-0-325) and call it done

[PLX]

Then it'll be a late 6G2 and all bets are off as to what Fender put in there. It was probably different from what was out into earlier 6G2s, because things were changing all the time. Try a 5E3 PT (325-0-325) and call it done

Just snapped this pic of the laydown PT that's in there.

[sluckey]

Does the amp work?

Using a ss rectifier rather than a 5Y3 will cause the B+ to increase.
 
Measure the PT secondary voltages with all tubes plugged in and amp working. What have you? Remember that with today's higher wall voltage, the secondary voltages will be about 10% higher.

Can you post some hi-rez pics of the amp?

[PLX]

Does the amp work?

Using a ss rectifier rather than a 5Y3 will cause the B+ to increase.
 
Measure the PT secondary voltages with all tubes plugged in and amp working. What have you? Remember that with today's higher wall voltage, the secondary voltages will be about 10% higher.

Can you post some hi-rez pics of the amp?

I thought the same thing, but wasn't getting that result.

My wall measures about 124VAC, on average.

This amp has been gutted. There's nothing left but the chassis, PT, and cabinet. Estate sale find.

[tubeswell]

Then hook the PT primary up to the mains (with a fuse) and see what you get on the secondaries

[PLX]

Then hook the PT primary up to the mains (with a fuse) and see what you get on the secondaries

362.4 & 368

wall : 123VAC

[sluckey]

Show us some pics of the chassis, inside and outside.

[PLX]

Show us some pics of the chassis, inside and outside.

[PLX]

Is it possible to use a zener to get that B+ down to about 280~300V ?

[HotBluePlates]

"Seeking spec sheet for 125P1A power transformer"

Schematic shows B+ of 315V, but I'm measuring over 400V

1.   Your photo shows nothing connected, so yes, voltage will measure very high because there's no-load.

2.   I used to own a 1965 Vibro Champ that also uses the 125P1A power transformer. I had to feed 107vac with a variac to get 6.3v on the heaters (because that amp only has 1x 6V6 loading the B+ winding).​  If the amp had the 2x 6V6 of a Princeton, something more like 117-120vac on the primary would have resulted in the correct heater voltage.
​​
3.   Once fed that 107vac my Vibro Champ supplied 323vac to the rectifier (not the 315v the schematic says) and delivered 366v to the 6V6 plate (over the schematic's 342v but pretty good). There was just-under 18v across the cathode resistor, which landed at a perfect idle current & dissipation.​


Bottom-line:  You cannot evaluate the voltage output of the power transformer without a power supply & power section circuit to load the windings.  You may also need a variac to feed a just-right wall voltage to the primary.

Is it possible to use a zener to get that B+ down to about 280~300V ?

If you do that before there's any load, the B+ will be down to 200v or less once the rest of the amp is there.

[PLX]

"Seeking spec sheet for 125P1A power transformer"

Schematic shows B+ of 315V, but I'm measuring over 400V

1.   Your photo shows nothing connected, so yes, voltage will measure very high because there's no-load.

2.   I used to own a 1965 Vibro Champ that also uses the 125P1A power transformer. I had to feed 107vac with a variac to get 6.3v on the heaters (because that amp only has 1x 6V6 loading the B+ winding).​  If the amp had the 2x 6V6 of a Princeton, something more like 117-120vac on the primary would have resulted in the correct heater voltage.
​​
3.   Once fed that 107vac my Vibro Champ supplied 323vac to the rectifier (not the 315v the schematic says) and delivered 366v to the 6V6 plate (over the schematic's 342v but pretty good). There was just-under 18v across the cathode resistor, which landed at a perfect idle current & dissipation.​


Bottom-line:  You cannot evaluate the voltage output of the power transformer without a power supply & power section circuit to load the windings.  You may also need a variac to feed a just-right wall voltage to the primary.

Is it possible to use a zener to get that B+ down to about 280~300V ?

If you do that before there's any load, the B+ will be down to 200v or less once the rest of the amp is there.

Thanks HBP !

I've been using this chassis & PT for years as a test bed for different pre-amp circuits.

I'm working on a circuit now that will only have two 12AX7's to produce a line-level output signal. No power tubes, no speaker load.

[HotBluePlates]

I'm working on a circuit now that will only have two 12AX7's to produce a line-level output signal. No power tubes ...

Then this power transformer has way too much current capability for your application.

For that scenario, even a Hammond 261C6 (one of their smallest) is overkill.

[PLX]

I'm working on a circuit now that will only have two 12AX7's to produce a line-level output signal. No power tubes ...

Then this power transformer has way too much current capability for your application.

For that scenario, even a Hammond 261C6 (one of their smallest) is overkill.

Exactly what I needed to know..

What about something like this:
https://www.antekinc.com/as-05t200-50va-200v-transformer/

[tubeswell]

Then hook the PT primary up to the mains (with a fuse) and see what you get on the secondaries

362.4 & 368

wall : 123VAC

Looks like 365-0-365 @125 wall voltage. No load. (Was the CT grounded?) as HBP says, those voltages will drop about 30-40 under load.

[PLX]

Then hook the PT primary up to the mains (with a fuse) and see what you get on the secondaries

362.4 & 368

wall : 123VAC

Looks like 365-0-365 @125 wall voltage. No load. (Was the CT grounded?) as HBP says, those voltages will drop about 30-40 under load.

Yes. CT grounded.

[Blind Lemon]

Guess I need to read a little closer . 


BL

[bmccowan]

I'm working on a circuit now that will only have two 12AX7's to produce a line-level output signal. No power tubes, no speaker load.

https://getyarn.io/yarn-clip/0c92dea4-3fc3-4dec-b85e-74dee386718f

[bmccowan]

And now less snarky this time: I might suggest that you build your line amp in another chassis/PT and build a 6G2 with that one? sweet amp and you can get the faceplate from Marsh or Mojo

[PLX]

And now less snarky this time: I might suggest that you build your line amp in another chassis/PT and build a 6G2 with that one? sweet amp and you can get the faceplate from Marsh or Mojo

I know.

I always get this response about this old chassis. 

Not into the kind of music that comes out of a 1964 Princeton Tremolo. I'm in the process of building a Bogner style pre-amp into this chassis to run into the front of my JCM800.

[thetragichero]

as long as there's enough filament current this sounds like a perfect case for the p-t290wx standalone reverb transformer. used to be able to get em for like 20 bucks when magnetic components was still around but i guess they're going for about 60

[PLX]

as long as there's enough filament current this sounds like a perfect case for the p-t290wx standalone reverb transformer. used to be able to get em for like 20 bucks when magnetic components was still around but i guess they're going for about 60

I asked in a post above about this transformer..

Looks like a better fit for the project, and it's $30

https://www.antekinc.com/as-05t200-50va-200v-transformer/

[sluckey]

Another good choice...

     https://www.tedweber.com/wrvbpt/

I used it in my Revibe project.

[PLX]

Another good choice...

     https://www.tedweber.com/wrvbpt/

I used it in my Revibe project.

Thanks sluckey !

What is the part number for the bridge rectifier chip you used in that project ?

[sluckey]

https://hoffmanamps.com/MyStore/catalog/parts20.htm

[DummyLoad]

as long as there's enough filament current this sounds like a perfect case for the p-t290wx standalone reverb transformer. used to be able to get em for like 20 bucks when magnetic components was still around but i guess they're going for about 60

I asked in a post above about this transformer..

Looks like a better fit for the project, and it's $30

https://www.antekinc.com/as-05t200-50va-200v-transformer/

yes, that will work fine.


--Pete