Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jeff on August 23, 2010, 02:12:07 pm

Title: Univox U-45B bad OT
Post by: jeff on August 23, 2010, 02:12:07 pm

I have a univox U-45B with a bad OT. The original OT was 16K.
I can't find one that's 16K but I do have an extra 8K OT lying around.
Is it ok to use the 8K and then run the 4Ω tap to a 8Ω speaker?
What are the drawbacks of doing this?

Title: Re: Univox U-45B bad OT
Post by: Geezer on August 23, 2010, 02:38:35 pm

Yes, that will work.......8k/4Ω becomes 16k/8Ω with an 8Ω speaker applied.

Drawbacks? None, but what is the relative size comparison of the 2x OT's? If they are ~~the same physical size, they should perform about the same. If the new OT is slightly larger, you may get a better low end response, or vice-versa if it is slightly smaller than the original.
Will probably work just fine or better, either way......

Geezer

Title: Re: Univox U-45B bad OT
Post by: PRR on August 24, 2010, 01:05:51 am

Plate supply voltage should be similar for similar bass-overload.

This suggests up-watting the nominal size. You would get back down to stock size by winding with a smaller gauge, but this is not an (easy) option.

Plate supply voltage is ~~280V. The world is full of 8K OTs for 6V6 at 280V-350V. Any of these will be fine (loaded 8r on the "4r" tap) if it fits.