Output Transformer for RCA BA-2 Build

[mbf90]

Hello,

I built an RCA BA-2 pre amp with 2 channels using Mullard ef37a tubes for the inputs and RCA 6j7 tubes on the outputs. I also used a pair of Altec 15095a transformers on the input and Carnhill vtb2290 transformers for the outputs. It sounds good, but I want to try a different set of output transformers as I want to see if a 5:1 15k primary type would perform any better than the 4:1 9.6k Carnhills. I narrowed it down to either a Sowter 1367 or UTC A-25.

I was going to go the Sowter route but not sure I want to wait that long to receive them. I emailed them asking for a an estimated delivery time but have not heard back so I’ve been looking at the UTC A-25s for sale. My question is do you think I’ll miss some low end with the UTCs? The Sowter has a better low frequency spec at least for the 5k source they state. The inductance seems competitively high on it as well at 100H. I think the UTC is 40H. I also wonder about the quality of the 1367 I would get now that Carnhill has bought Sowter and whether or not they have been able to replicate it.

Any help/info is appreciated.

Thanks,

Matt

 

[rock soderstrom]

Hi Matt, interesting project. I like the Ef37a, a good sounding and really beautiful tube!

Some photos of your amp would be nice.

On topic, here links to two UTM transformers, they could fit your project, price is good. Both are 9.6k:600R, too! I have no experience with them in your circuit but if you try them, lets us know how good they are.

https://utmindustry.com/utm3590b/

https://utmindustry.com/utm3590/

Cheers

 

[beatnik]

There is also Lundahl 1680 and Cinemag has a few candidates as well which could be made with the high nickel cores this would sound different than a steel core transformer.
The UTC must be 300 dollars a piece right now. Doesn't make any sense to me.

 

[jazzcrisis]

Hi Matt, interesting project. I like the Ef37a, a good sounding and really beautiful tube!

Some photos of your amp would be nice.

On topic, here links to two UTM transformers, they could fit your project, price is good. Both are 9.6k:600R, too! I have no experience with them in your circuit but if you try them, lets us know how good they are.

https://utmindustry.com/utm3590b/

https://utmindustry.com/utm3590/

Cheers

I tried these in a stock BA-2 circuit and the low end was *not* acceptable. Rolled off way too early. Swapped to an A25 and all was well.

 

[rock soderstrom]

I tried these in a stock BA-2 circuit and the low end was *not* acceptable. Rolled off way too early. Swapped to an A25 and all was well.

Thanks for feedback! What a pity!

 

[My3gger]

Thanks for feedback! What a pity!

Here we think roll of at 40-50Hz isn't a problem with this one, one that did go lower wasn't sounding different.
I believe harmonics make up for what is "lacking" in frequency response.

 

[emrr]

-1dB to -1.5dB point roughly 30Hz in the real thing.