Sluckey's Bucking transformer

[Willabe]

I might build 1 or 2 of these for my friend. He has variac's that he takes to gigs with him, but a bucking transformer would be smaller and lighter.

His BF DR B+ is 440DCV with a 127ACV from the wall. 

I set my variac for 120ACV and the amps B+ came down to 420DCV.

And his Bassman 135 isn't the export model with the PT primary taps. The schemo for that amp shows 500DCV B+ CT DCV with a wall ACV of 120. So that amp could really use a bucking transformer too.

How do you figure out how many amps you need for the bucking transformers rating? Is it according to the amps power fuse? 

The Radio Shack PT in you used in your Buckaroo is 3A. Nice price and easy to get, I would think that would handle the BF DR easily, but that Bassman 135 is a big 4 X 6L6 beast.

         

[sluckey]

I would use a transformer that has a current rating at least the same as the amp's fuse. This 4 amp PT should handle the DR or the Bassman.

https://www.tubesandmore.com/products/transformer-hammond-filament-126-vct-4

[Willabe]

Thank you. 

I have some toroid PT's laying around that I bought on close out from AES.

Do you think they would work?

[sluckey]

yes

[jjasilli]

I would use a transformer that has a current rating at least the same as the amp's fuse. This 4 amp PT should handle the DR or the Bassman.

https://www.tubesandmore.com/products/transformer-hammond-filament-126-vct-4

Yes, but note that these trannies tend to run hot, maybe too hot to touch.  This is OK operationally but could burn an unwary user.  If you go for a higher Amp rating to run cooler, you'll probably have a higher output voltage, thereby causing a larger bucking voltage drop.


Note that the lowest safe voltage is to not allow the filaments to drop below about 5.2V