Old tranny - confused with windings

[Brit01]

Just got a big dirt cheap tranny.

I was told it has 350-0-350 (450 watts), 5V secondary, 6.3 V secondary @ 5 amps.


No markings and confused with which is the primary.

On 1 side it has 2 outputs:

1st output: 2 very thick wires and 1 very fine wire. 1.2 ohms between all of them. If this is the primary shouldn't it have a higher resistance? And what is the thin wire for?

2nd output: 2 thin wires with 5.6 ohms resistance (maybe the 6.3V?)

On the other side:

1st output: 2 thick wires with a 1.2 resistance (maybe the 5V)

2nd output: 3 very thich wires, 62 ohms between the 2 and 124 ohms between the 3rd (i assume this is the 350-0-350).

What's the best way to test this? I was informed it was working fine.

[Ty_Bower]

Originally Posted by Brit01

What's the best way to test this? I was informed it was working fine.

Get yourself a 10 ~ 12 VAC supply. Dig through your box of old wall warts; chances are you will find one that will work. Take your best guess as to which winding is primary, and connect it to that. Measure what comes out of each of the other windings. Now scale the results to calculate what you'd get if you had connected line voltage (120 VAC) instead of your test voltage (10~12 VAC).

The primary winding is often black, white, or blue. High voltage secondary is often red or orange. Heater windings are typically green, yellow, or brown. Good luck!

[Brit01]

Was just thinking of the same thing. Got an old switchable ac wall outlet. I'll give this a go.

Also taking the casing apart found another small very fine wire coming from the second output on the first side. Strange. maybe the 5v and 6v windings have CT.

[BZed]

I would think that side 1 output 1 would be the 6.3 volt filiment winding with a center tap ground. The second winding on side 1 is most likely the primary. On side 2 output 1 is most likely the 5 volt winding for a tube rectifier and the # 2 output is the high voltage winding. The low voltage high current windings are going to be the lower in resistance windings. The very fine wire you found inside may be an internal shield ground connection between the primary and the other windings.

I would use the transformer test suggested by Ty.

Good luck
BZ

[Brit01]

Just tried it first with the 12v and now with 220.

Yes 1st side is the primary and next to it reads 6v (reads ~6-7 without load).

2nd side I'm getting 440V without load and the other secondary wavering around 5V.


It's buzzing quite a bit.

Is this normal with these giant (about 10-12 kilos, 4-5 inches wide) transformers or is indicating a problem?

[BZed]

Taking one of those old transformers apart causes you to break the varnish that coats the windings, core and cover. One of the main reasons to varnish dip transformers was to keep them from buzzing. The other is to seal them from moisture. Make sure to replace the covers and tighten the bolts, that may help the buzzing because it clamps the laminated core and its the core that buzzes most of the time.

BZ

[Brit01]

good to know.

yes I have stripped the wires, cleaned the rust of the laminates front and sides and will repaint the end covers (not shown in the photos as they are removed).

So once the bolts are replaced and tightened maybe I have less buzzing.
Mind you I have a big Carver SS power amp and that thing vibrates like a train.

See the pics, I found these fine wires between the 6 and 5 v secondaries.
Can I just tape these up and leave them?

[BZed]

Are they connected to any of the windings? Check with ohm meter. If not connected to windings they may be ground for interwinding shield. Was the end of the fine wire traped under the end bell/cover? That would be an indication that they are interwinding shield ground.

BZ

[BudP]

When you go to replace the endbells make absolutely certain you have replaced the isolation washers, usually a fiber washer and paper tubes from the old days. Even better go to one of the modern hardware stores and look in their bearings section for molded nylon parts with a washer and barrel that just fit over the bolts. Use these T barrel items as isolation. Put them under the head of the bolt with the barrel sticking down through the end bell and core bolt hole, assuming you have corner bolts. Side bolted end bells are just as impo0rtant in terms of insulation of the bolt head from the end bell metal.

Doing this will avoid an eventual, or sudden core short, resultant high current in the primary, potential fire, lot's of evil smelling smoke that will last for weeks and of course, transformer death.

[Brit01]

Are they connected to any of the windings? Check with ohm meter. If not connected to windings they may be ground for interwinding shield. Was the end of the fine wire traped under the end bell/cover?

One of them was under the end bell/cover. The other no, it had an old perished cable cover but only at the beginning.

I did get a reading on the one with the old cover so I assume this is the CT.

So if the other has no reading it's the internal shielding ground and this must be pressed between the bell cover once replaced.

When you go to replace the endbells make absolutely certain you have replaced the isolation washers, usually a fiber washer and paper tubes from the old days. Even better go to one of the modern hardware stores and look in their bearings section for molded nylon parts with a washer and barrel that just fit over the bolts. Use these T barrel items as isolation. Put them under the head of the bolt with the barrel sticking down through the end bell and core bolt hole, assuming you have corner bolts. Side bolted end bells are just as impo0rtant in terms of insulation of the bolt head from the end bell metal.

The end bell/covers were bolted directly to the laminate core. Should there be insulation between the end bell and laminate?
If there is no insulation what use is insulating the corner bolts if you don't mind me asking?
I'm understanding now the insulation washers need to go between the end bell/cover and laminate core through the bolts no? So there is no contact between the end cover and laminate?
BUT according to the comment above the internal shield wire was compressed between the bell cover and laminate.
I'm a little confused now.

Thanks in advance for your advice.