RCA BA-2B with the wrong output transformer?

[mrtnasty]

Hi I recently acquired an RCA BA-2B preamp, the input transformer is the right one labeled 901046, as in the schematic, but the output transformer is not the 901740 from the schematic, it is labeled M-146729 and has UTC F-1234 printed on the outside, and the pin layout is definitely not the same as the 901740 transformer. Anyone know what this transformer is, if it's actually the wrong transformer, and where I might find the right one? Thanks!

 

[emrr]

Offhand that sounds like a BA-11 output. Rectangular?

 

[mrtnasty]

Offhand that sounds like a BA-11 output. Rectangular?

Hey thanks for the reply. No it's circular, here's are some pics.

 

[mrtnasty]

The pin layout and DC resistances (according to the BA-2B schematic) of the transformer in question are the same as the input transformer. Im pretty sure this BA-2B has 2 input transformers.

 

[dmp]

The F-1234 is the input transformer to the BC-2B console preamps. So it's not going to work where it is. It is basically the same as the input on yours, as you discovered.
Finding an original output transformer for a a BA-2 is going to be be difficult. Put a watch on ebay and search occasionally and maybe in 10 years you'll find one. Be prepared to spend $$$.
In meantime you could get it working with a substitute (nondestructively mounted I'd advise, ie. don't drill any holes in that chassis), but it's a transformer coupled output so the transformer needs to be gapped to take ~8mA of current. Search the BA-2 threads to see discussions of subs

 

[mrtnasty]

The F-1234 is the input transformer to the BC-2B console preamps. So it's not going to work where it is. It is basically the same as the input on yours, as you discovered.
Finding an original output transformer for a a BA-2 is going to be be difficult. Put a watch on ebay and search occasionally and maybe in 10 years you'll find one. Be prepared to spend $$$.
In meantime you could get it working with a substitute (nondestructively mounted I'd advise, ie. don't drill any holes in that chassis), but it's a transformer coupled output so the transformer needs to be gapped to take ~8mA of current. Search the BA-2 threads to see discussions of subs

Alright, thanks for the info!

 

[TwentyTrees]

UTM (@igs) do a gapped output transformer which I understand is intended for BA-2 style applications - I've not used it, but its certainly a more wallet-friendly option than the original iron or other alternatives (Sowter, Cimemag, UTC etc):

UTM3590 – UTM Industry

 

[mrtnasty]

Would the output transformer from a Collins 212y work well as a substitute?

 

[mrtnasty]

Actually there is one on Ebay now:

https://www.ebay.com/itm/1159643369...-81f7-d2895f53c0ef|iid:1|vlpname:vlp_homepage
I don't think it's exactly the 212y output, its number is 0058, not 0066. Anyone know this one?

 

[dmp]

That one is designed to take DC but it is a 4:1 ratio (sqrt(10k/600)). The BA2 uses a higher ratio, like 7:1
Will it work? yes. Will it sound right? You'd have to try it to see. A lower ratio loads the tube more compared to the higher ratio.
Did you read through the other BA2 threads that discuss the transformer? Lot's of info already here.

 

[emrr]

Actually there is one on Ebay now:
I don't think it's exactly the 212y output, its number is 0058, not 0066. Anyone know this one?

0058 does not take DC

 

[mrtnasty]

0058 does not take DC

Thank you

 

[CJ]

Some folks have used the UTC A 25, Cinemag CM 2092G and Lundahl LL 1680 for this project.

Consider selling your UTC F 1234 on evilbay to finance your output.

Are you sure you have a BA-2a and not the BC? Does the UTC out look like it has been transplanted or does it look like it has been there since the caveman days?

 

[CJ]

This is the 2A outy
Which could be easily tweaked for the 2B,

I bet can and core are the same,

See that the core is not butt stacked.

It is what's called "Lap 15" and we ain't talkin billy bob Nascar and bass,



https://cdn.imagearchive.com/groupd...50650d47b1805219fccbf220b3c4543aac1e9e9f352e1

 

[mrtnasty]

Some folks have used the UTC A 25, Cinemag CM 2092G and Lundahl LL 1680 for this project.

Consider selling your UTC F 1234 on evilbay to finance your output.

Are you sure you have a BA-2a and not the BC? Does the UTC out look like it has been transplanted or does it look like it has been there since the caveman days?

I acquired the BA-2B and a couple BC-2B preamps from the same source. My guess is they had more BC-2B preamps and swapped the transformers for some reason a long time ago. The BC-2B's need restoration, and once I make sure they all work, I plan to sell the extra F-1234.

 

[mrtnasty]

Does anyone have any information on the following RCA transformers?

XT-1963-B
XT-2016-B
XT-2432
XT-2433
XT-2484
900781
900782
900783