higher voltage on OT than originally called for

[thehoj]

On my Bogen chb-35a, the way I have it set up right now I have 490v on the OT.. Originally the schematics show 460v as being the source for this.. Is it likely that I'm going to burn it out quickly doing this?

[Old Tele man]

...depends on how old the tranny is. It used to be pretty much standard engineering practice for PT's and OT's to be sized 50% over normal use requirements.

...the problem is that way back then, the paper interleaving between the windings and winding coatings were probably at least 150%, but over the intervening years things have dried out and become brittle, so that extra 50% of reserve rating might NOT really be there today.

...that said, I'd guess only +30V probably won't hurt, but we really have no way of knowing...until something fails, then, you know.

[thehoj]

Just trying to get a feel for what kind of thresholds these old transformers might have.

Is there anywhere to get specs on the tranny's for these bogens? I have no idea what kind of replacement I would even get if this thing went.

[olddawg]

If the problem is that the B+ is too high you can always lower it a bit with a couple of 10v 5watt zener diodes in series. Three of them would reduce your B+ by 30v. It's done all of the time and the zeners are only a couple of dollars. You can even switch them in and out. Just mount them where thay can breath a little.

[Enzo]

It is not even a 10% variation. I wouldn't worry about it.

[Robert M. Martinelli]

I'm with Enzo on this one...old Fender amps' schematics called for a 20% tolerance on voltage measurements, and many of them worked very hard through the years and managed to survive....

This said....and just because I'm curious, have you checked what your mains voltage is? If the amp was designed with, say, 110 VAC in mind ( don't know which side of the pond you are on ) and your mains voltage is, say, 120 VAC, that would explain the phenomenon.

Cheers

Bob