Altec/Peerless 6367 power transformer info?

I've been given a peerless 6367 power transformer taken from an old Altec consumer home stereo preamplifier which used only two 12AX7's as active components. I'm wanting to use this thing to power a couple of Jakob's SRPP output stages, but don't know how to connect it (it has been removed from the unit and the rest thrown away). I don't know the model of the Altec piece it was taken from, but I understand it was a gold color, if that helps date it.

Does anyone happen to have information on this transformer or know where I can find it?

FWIW, it has two green leads (fairly thick) and on the other side two black, two red, and one yellow lead -- all equal but smaller gauge wire than the green.

Thanks so much for any help!

Peace,

JC

If it follows standard practice, and it probably does:

Black: primary

Red: high-voltage winding

Yellow: probably centertap of HV winding, or possibly of heater winding. Confirm with ohmmeter.

Green: filament

Thanks, Dave, that does appear to be correct. The yellow is, in fact, the center tap of the green, and this color scheme seems to be fairly consistent in most of the Altec tube circuit schematics I've been able to find.

Can you tell me how to test this transformer for the secondary voltage? I used my multimeter to check continuity of the windings, and only the green wired sounded. The reds and blacks made no sound, and when I measured them with an ohmmeter the black leads read 65 ohms while the reds measured 250 ohms (the greens measured 0.00). I'm guessing this means there's more length in the red secondary??

How can I find out the voltage for the red? Is it just a matter of hooking the black leads up to the wall and measuring the reds, or do I need to put together a test circuit?

Thanks for all the help.

Much peace,

JC

> power transformer taken from an old Altec consumer home stereo preamplifier which used... 12AX7s... it has two green leads (fairly thick) and on the other side two black, two red, and one yellow lead -- all equal but smaller gauge wire than the green.

First, be sure where it came from: 120-Volt-land or 230-Volt-land. In Plano TX, 120V is most likely, but beware gifts from Brits.

You know, from the 12AX7 use, that it is probably 120V, 6V or 12V, and about 200-300V. And that the 6V-12V is higher current than the rest, so the fat wires may be the low voltage. Or they could be well-insulated wall-voltage. But Black is almost always wall-power. And Red is almost always the Plate power (200-300V).

> I used my multimeter to check continuity of the windings, and only the green wired sounded.

Darn it, don't use a too-clever buzzer to measure transformers. The high voltage windings are higher resistance than a "continuity tester" generally reads, plus the high inductance really confuses many digital meters that pulse the test current. (I nearly threw-out a perfectly good plate transformer that way: digi-meter said "Open" but it was fine.) The old $15 analog meter is better.

> the black leads read 65 ohms while the reds measured 250 ohms (the greens measured 0.00).

Another clue that the Red-Red voltage is -probably- higher than the Black-Black voltage. And 12AX7s usually get fed higher than 120V power, if possible.

0.00 on the Green-Green is wrong. 0.1 is more likely. Again some digi-meters "cleverly" round-down low readings. I have one that doesn't, and it reads 0.1 ohm with the probes tightly shorted, which is why they force "low" readings to a nice neat "zero". The other possibility is that this iron is wandering loose in the world BECAUSE it has an internal short and was replaced, but didn't end up in the trash.

If you are brave, connect the Black-Black to 120V and see what comes out. If you are smarter than that, splice a 60 Watt lamp in series with the transformer and the wall: if the transformer is dead-shorted, you just get 60 watts of light, instead of blown fuses or fires. Be VERY CAREFUL: we know there should be hundreds of volts in there somewhere. Connect your meter with clip-leads with the power off, stand back, plug-in, wait for slow fire, then check your meter.

Or to be very conservative: get a 12 V AC transformer. Connect about 100 ohms in series with the 12V side. Connect that to the supposed 120V wires. Now all the voltages should be about 1/10th of what they will be when running 120V, and if anything does not make sense then you can think about it without any annoying smoke in your eyes or very deadly voltages within reach. If the Red-Red read say 20V, you have about 200V, suitable for about 270V DC. And the Green-Green should show either 0.6V or 1.2V, implying 6V or 12V heater supply. That assumes the 12V across the Black-Black stays 12V. If it is significantly less than the 12V feeding it, and that 100 ohm resistor gets hot, it is drawing unusual current for a small transformer and is probably shorted.

Okay,

I finally got around to measuring the secondaries of this thing with the primary (black wires) in series with a 60W light bulb. The bulb didn't light at all, and the measurements are:

red leads -- 128 volts AC
green leads -- 7.48 volts AC (the yellow is CT)

Now I'd like to measure the amps coming off each winding. Is there a proper way to do this other than just plugging it straight into the wall? Doesn't it have to be under a load of some kind?

Thanks so much for the help with this!

JC

> Now I'd like to measure the amps coming off each winding.

You can't.

OK, right now there are "no Amps" coming off. (Maybe 10 uA for your meter.)

Short the 128V output, and you "can get" probably 100 milliAmps. And in a minute, as a bonus, Big Smoke, folowed by Death Of A Transformer.

Current "rating" could be based on either voltage drop or heat. In big transformers, usually heat. In small transformers, voltage drop may get excessive before the tranny really cooks.

You know one thing: the heater winding is made for two 12AX7, 3.6 Watts total. It has to be that much, if your information "taken from... stereo preamplifier... two 12AX7s" is correct. It won't be any more, because mass-produced hi-fi can custom-order just-big-enough transformers, and Altec wasn't paying for big iron in little preamps.

Yo also know that this thing has lots of voltage drop. The heater winding will surely be about 6.3V at 0.6 Amps, but you see 7.5A at zero Amps. 18.7% drop from no-load to full-load. That's actually typical for small transformers.

The plate winding is hard to guess. It "must" supply about 4mA DC, what a two-12AX7 preamp would eat. But wire just-big-enough for 4mA is awful small, hard to work with. It may be able to carry more current without excessive loss or heat. Or it may not.

Leave the 60W lamp in there. Load the heater winding with two 6V 0.3A heaters or a 10 ohm 5 Watt resistor (or ten 100 ohm 0.5W resistors paralleled). Should get about 6V AC. It is OK if it reads a shade low, because we have that 60W lamp in there for safety.

Let it cook for an hour. We know it "should" be OK this way, because Altec sold it for this load. But you want to find out how hot it normally runs with heater load, so you can judge how much hotter it runs with the HV load added. Finger-touch is good enough accuracy.

Then let it cool while you add a 400V 1A bridge rectifier and 200V 100uFd cap on the "128V" winding. You should get 160V-180V DC no-load. Load it with about 50K ohms 1 Watt of resistors, then another 50K ohms 1 Watt of resistors in parallel. These give currents of about 3mA and about 6mA. See how bad the DC voltage drops. Go ahead and load it until it drops 20% from the voltage you got with full heater load and zero HV load.

Now let it cook, but keep feeling the transformer. If it gets hot fast, you are pulling too much load, you will have to take less HV power.

I really bet it is just-good-enough to deliver 150V DC at 3 or 4 mA. That would be just right for a two-12AX7 phono preamp. If you try for more current, it will either sag to 100V DC or it will run too hot for long life. If you use a voltage-doubler to get 250V-300V DC (like most Pro audio), then the current rating will be half, maybe 2mA, which isn't much good.

That iron was specified and bought to drive two 100K loads to maybe 10V peak. Using simple circuits (and you don't have the heater power to do anything complicated), it is unlikely to be big enough to drive two 10K loads to even 10V peak, the minimum for interfacing to any "Pro Audio" gear. It is just too small.