Peavey Classic 50 repair

[jmaroto]

Hi I bought an old very beated peavey classic 50 and reparing other things (one was the power transformer) I think the OT possible faulty.

Everytime I try to connect the center tap to the power board the fuse blow. I did the 9V battery test and everything seems fine. Also tryed 0.75V AC on the sencondary, one side of the primary reads 15V and the other shows 13V.

Does anybody think this difference can be the cause of the fuse blowing?

[Jazz P Bass]

I would suggest that you remove all of the tubes.
Try powering it up now.
If it still blows the fuse, disconnect the red B+ wire to the OT primary.

[jmaroto]

Thanks for the tip Jazz P Bass, I'll place the OT back and do that test.

I just did another test but I'm not really sure if it's relevant. Tested the resistenace between the primary and the secondary, One side of the primary tested about 100 Ohms resistance with the secondary, but the other side and the center tap barely reach 18 Ohm resistance.

Could this mean something relevant?

[J M Fahey]

Can't be, there's not continuity between primary and secondary.
Maybe you mis-identified some wires.

[jmaroto]

I wish I had, but the secondary and the primary are well identified on the schematic.

Brown / Blue / Red = Primary

White / Orange / Green / Black = Secondary

[J M Fahey]

please tell me which primary wire has what resistance to what secondary.
I assume you are measuring the transformer unmounted from the chassis, sitting on some insulating base such as wood.
Better yet, draw a small sketch of primaries and secondaries, and post resistance of each winding and resistance from primary to secondary.
Also measure whether any winding has some resistance to the iron core.
Anyway I think your OT is shot, but I'd love to confirm.
Sorry

[jmaroto]

Yeap Fahey, I'm testing the OT on my wood bench, nothing attached to it.

Here's a drawing of the measurements, so far I think is bad, since the Power Transformer on this amp was bad also.



Thank you

[J M Fahey]

Sh*t!!, it's shorted then, that's why when you connect Red to B+ your rectifier sees an 18 ohm load (which to it is practically a short) and blows the fuse.
Can you get another similar one or will have to rewind it?
Good luck.

[Jazz P Bass]

With resistance like that from the primary to the secondary, the OT, she's a no good.