50watt partridge transformers. Help please =]

[Yrps]

Black red @ 60Hz=407mV
Green1=18mV
Green2=276mV

[The Dude]

Sorry. And really, I'm not trying to be a pain. I'm not sure what the two "Green1" and "Green2" readings mean or what they are referenced to? We have the primary 407mV. That's good. Now simply measure from one green wire to the other green wire and report the AC voltage there. One reading across the two green wires.

[Yrps]

Across both green wires I got 230mV. Not being a pain. I'm sure I've caused a few groans.

[The Dude]

If these readings are correct, the ratio would be approximately 1.77:1 (407/230) meaning if you put 115V on the red and black primary wires, you should get around 65V on the green wires unloaded. At 220V about 124V (I'm not sure where you are located). At around 12V supplied, the green wires would already be around unloaded filament voltage. You might try some other primary wire combinations and/or measure other secondary wires.

Possible Conclusions?

1) The green wires are not for filament supply. (I guessed wrong)
2) Supply voltage was too low for accurate readings.
3) The correct primary wire combination has yet to be discovered.
4) Other

My apologies for running you in circles with not much to show for it. You have the idea anyway. I've done this with a tone generator before, although it had a much higher output voltage. It would certainly be easier with a variac. You wouldn't need a calculator.

[g1]

Do you happen to know the Sound City model these were pulled from?

[Yrps]

Nah. It's from a 50watt P.A system. I found one schematic that could be it from the soundcity site. But I could also be wrong.
http://soundcitysite.com/SoundCityPA50RSchem.pdf

[g1]

That's for a solid state model.
But I think I have your PT info. You will need more AC voltage for your testing to verify, at least a couple volts.
PT primary
black - common
red - 240V
yellow - 120V
white -frame ?

PT secondary
greens - heater (6VAC)
browns - bias winding (30VAC ?)
black HV common
red HV (400VAC ?)

[The Dude]

Solid state model with a tube output stage. I agree with your assessment g-one. It's what I was thinking based on the resistance measurements. Lowest resistance being the heater windings and highest being the B+ windings. It would certainly make sense. I'm still on board with that and possibly we just didn't get accurate readings due to the low input voltage.

@ Yrps: Do you have just a small 6V, 12V, (whatever) transformer laying around you could use to supply a test voltage?

[nsubulysses]

I know I'm late to the game and you're all probably already beyond this, but this helped me understand

[g1]

Solid state model with a tube output stage.

I didn't even catch the tubes!
Looks like a pretty good schematic representation of this PT, just this one only has 2 primary voltage choices, and no heater center tap.

[Yrps]

I don't. But, I'm heading out soon and might see if I can find one. Something like this, perhaps? 12V-0-12V 20VA Toroidal Transformer - Low Profile - Jaycar Electronics

[The Dude]

You don't even need to spend that much money. Something like this will do. Current will be negligible with no load.

12.6V 300mA PCB-Mount Miniature Transformer - Radioshack

[The Dude]

While we wait on that, on to the output transformer.

The schematic you uploaded should be very similar to the OT you have.

The primary side (4 wires): 3 of those will be the winding with center tap. The other? Maybe the frame? You can measure the resistance of those wires to figure out which is the center tap. The center tap to each outside will read the same resistance.

The secondary side looks to be much the same as the schematic you posted. Fortunately for you, the 100v wire is labeled. Measuring from that wire to each of the others, one of them will have more resistance than the others (probably 'E' if labeled in order). This one will be speaker negative. Then look at the schematic. We have a 4, 8, and 16 ohm taps. Measure from the speaker negative wire to each of the other 3. The lowest resistance will be the 4 ohm tap and highest the 16.

[The Dude]

The schematic shows a 100v tap out of the OT secondary. I'm thinkin' of it driving a "transformered" line. Also, there are 5 wires on the secondary in the pictures and one of them is heat shrinked off like it wasn't used. I'm guessing that is the 100V tap on the output. The other 4 would be common, 4, 8, 16 ohm.

Maybe some picture confusion here also? I'm seeing the first two pics as the PT and the second two as the OT.

[g1]

Sorry Dude, I deleted that post as I was looking at the wrong picture. Duh.
I missed breakfast. They say it's the most important drink of the day.