jtm60 output transformer

[clearwaysteve]

Hi just fitted new output transformer to my jtm60. Its larger than the original (upgraded version made by dagnall) The wires are connected to different posts on the transformer but don't know which ones! can anyone tell me which colour wire to what number on the transformer terminal? Regards Steve

[Steve Conner]

Did you try phoning Dagnall?

[Robert M. Martinelli]

Xformer measurements

Hi,
I suppose you do have the schematic diagram, so at least you know where each wire COMES from; at this point to map the xformer' s connections you should measure the output xformer windings using a multimeter capable of reading both high and low resistances with good accuracy.
Of course I' m talking 'bout taking the measurements with the xformer completely disconnected and no power whatsoever around.....

You' ll need a good deal of patience, putting one probe on one wire of the xformer with an alligator clip, and alternatively searching the other end of that winding until you get a reading other that infinite.

Write down the reading and proceed with the other wire to identify the center tap or the other end ( if the next reading you get will be about the half of the previous one you have found the center tap, if it is about double the first wire was the center tap and the last you found was the other end ).

The primary winding will have the greater DC resistance, and the center tap ( which goes to the +anodic supply in a push-pull AB1 class amp ) should measure approximately half of the total primary winding resistance. The start and the end of the primary winding will go to the anodes of the output tubes. The secondary winding will have a much smaller DC resistance, with a center tap or two for different impedance speakers.
At this point simply follow the schematics to wire the xformer.
I know there would be a lot more to say but I believe this to be a good starting point.
Hope this helps
Good luck!
Regards
Bob

[clearwaysteve]

reply

I.m in australia

[clearwaysteve]

reply

Thanks but can't read schematics even though have a copy. My tech is out of town a week and have rehearsals tomorrow. Don't know if schematic is referring to old or new transformer. There are more terminals on the new one. Thanks anyway If anyone had a photo showing connections would solve the problem. But I can't find any on the net