Mystery Transformers

[Blueboozer]

Last August I purchased a couple of transformers from a TAG member who was cleaning house. They have no markings and the wire colors are non standard.

I decided to dig them out today and document their configuration. It’s definitely not standard. Custom wound maybe? They’re both pretty hefty and look like they’ve had a rough life. The seemed pretty steady on the voltages without a load.

I’ve found the OT should work for KT88’s, 6550’s, or KT66’s. Not sure about the PT. Does anybody have any idea what these might be out of? 

[uki]

The PT can do about 532vdc ( 380 * 1.4) with SS rectification, can feed a pair of KT88 or similar tubes, or a quad of 6L6GC, from what it came out I dunno.
Rectifier tubes go from 1.1 to 1.3.

Show us some pictures please!

[kagliostro]

To establish the disposable currents on an unknown PT you must put a load (resistors with oversized power dimensions and adequate resistance value) on each winding (HT & Heaters) go with a load that lower the voltage value (with respect what you measure with your voltmeter) of a 5%, then wait 1/2 hour looking to the transformer temperature increase, if it will rest reasonable you can consider the current load you applied the max current that the unknown PT can supply, otherway you can decrease the resistance value of the resistors and repeat


I hope I expained this thing in a comprensible way


Ciao


Franco

[Blueboozer]

Thanks Kagliostro, I'll give it a try

[kagliostro]

PRR surely will be more able to explain you the exact procedure to follow


Franco

[trobbins]

Loading each winding reduces the measured voltage due to internal winding resistance.  Waiting say 30 mins to an hour allows the copper winding to increase in temperature to a level more likely experienced during normal operation, and that increases the winding resistance a bit, which also would lower the measured voltage.  The 5V winding would typically be good for 2A, and possibly 3A, as they were the common rectifier heater current levels. 

The physical size of the core will indicate what VA rating the transformer may be good for - that requires comparisons with known transformers.  Measuring the DC resistances of the primary and secondary HT windings can also be a reasonable comparison with other known transformers.

Loading the 6.3V and the 380-0-380V windings requires a bit more technical effort to derive a reasonable load resistance to apply, especially for the 380-0-380V windings as they would be rectified and filtered in a normal amp.  If you aspire to a KT88 PP amp then you may want to use a 4A loading on the 6.3V to confirm ok operation.   Although you could put a resistor across each HT half secondary (380-0V) winding it may be better to set up a temporary ss rectifier capacitor filter and load the DC output - say to a typical idle current requirement like 100mA.  A lot of effort to make, but it can avoid making up an amp and then realising the PT doesn't actually suit.

[Blueboozer]

Loading each winding reduces the measured voltage due to internal winding resistance.  Waiting say 30 mins to an hour allows the copper winding to increase in temperature to a level more likely experienced during normal operation, and that increases the winding resistance a bit, which also would lower the measured voltage.  The 5V winding would typically be good for 2A, and possibly 3A, as they were the common rectifier heater current levels. 

The physical size of the core will indicate what VA rating the transformer may be good for - that requires comparisons with known transformers.  Measuring the DC resistances of the primary and secondary HT windings can also be a reasonable comparison with other known transformers.

Loading the 6.3V and the 380-0-380V windings requires a bit more technical effort to derive a reasonable load resistance to apply, especially for the 380-0-380V windings as they would be rectified and filtered in a normal amp.  If you aspire to a KT88 PP amp then you may want to use a 4A loading on the 6.3V to confirm ok operation.   Although you could put a resistor across each HT half secondary (380-0V) winding it may be better to set up a temporary ss rectifier capacitor filter and load the DC output - say to a typical idle current requirement like 100mA.  A lot of effort to make, but it can avoid making up an amp and then realising the PT doesn't actually suit.

Thanks for all of this info.

Labbing this up will be one of my weekend projects.