Rca ba6a transformer specs

[Thegoldenlockedlamb]

Hello everyone!

I am wanting to either have a winder build clones of the Rca ba6a input , interstage , output and possibly power transformers if need be . I was wondering if anyone know the specs to them? Or any info I would to give a winded to build them or even possibly so I could maybe find some old transformers with the same specs that aren’t crazy expensive is another option .

Also if anyone on here is interested in winding them please feel free to reach out !

Thank you all for your help !

Best,

Ethan

 

[Flundran]

Have you considered Sowter tranformers?
SOWTER VINTAGE AUDIO TRANSFORMERS

 

[Rob Flinn]

Maybe do a search here for this, there are a few threads concerning these transformers.

 

[emrr]

If we haven't covered it in all the existing threads, it's not known by me. You'd have to tear some down to really know what the manufacturing specifics are, then it's likely there'll be something that'd be custom and unobtainium today, if trying to be specific. Almost no one winds with as many turns of as small a wire gauge today as they used to. That's a whole thing a modern winder will fight you about.

 

[Thegoldenlockedlamb]

Have you considered Sowter tranformers?
SOWTER VINTAGE AUDIO TRANSFORMERS

Hey my friend ! I have considered them , but have read threads on here where a few have mentioned they aren’t 100% accurate to the originally, plus they aren’t cheap . But In the end I may have to go that route . Thank you for your reply

 

[Thegoldenlockedlamb]

Maybe do a search here for this, there are a few threads concenring these transformers.

Yes I think you’re right , I dug for a few hours through threads a few days ago and didn’t find exact specs, though I feel like I have read it on here at some point. I guess I’ll keep looking. Thank you for your reply .

Also aren’t you the guy who built the API style console a few years ago? If so that is a really awesome build !

 

[Thegoldenlockedlamb]

If we haven't covered it in all the existing threads, it's not known by me. You'd have to tear some down to really know what the manufacturing specifics are, then it's likely there'll be something that'd be custom and unobtainium today, if trying to be specific. Almost no one winds with as many turns of as small a wire gauge today as they used to. That's a whole thing a modern winder will fight you about.

Yeah I’m pretty sure at some point you guys have covered it to some extent . I did find an old post on gearslutz where a guy asked you what you thought the specs were. You said you didn’t have one on hand but had a guess the input would be somewhere around 600:50k or 600:100k , interstage either 30k:30k or 50k:50k and the output 5k:500 , do you still think that could be the case today ? Thank you for your reply and I attached a picture of the post on gearslutz.

 

[emrr]

More or less right. The output is 7k7:500

 

[Thegoldenlockedlamb]

More or less right. The output is 7k7:500

Thank you ! I actually bought the input transformer for a ba-25 last night that the description claimed was 600:50k , but I have no idea if that is correct . Do you know anything about it ? I thought for $50 it was worth a gamble . I also found a transformer company in Poland called utm, I noticed they had some low priced transformers , they are more in line with sowters input transformers 600:10k etc. any experience with those ? I know the owner is a member here .

Thank you again for your time , help and patience !

 

[dmp]

You need a center tapped secondary on the input transformer for it to work on a BA-6A. Look at the schematic.
The control voltage for a vari mu is sent to the center tap.
The BA-25 schematic does not show a center tap.

 

[dmp]

The interstage primary is also shown with a center tap and is operating as a push-pull.
These are very special transformers to the design. Not common. Good thread here that addresses your question on many levels.
If you don't want to spend the amount $$$ needed for authentic (either vintage or sowter), some circuit redesign would allow more common transformers to be used. See DaveP's comment in the above link.

 

[Thegoldenlockedlamb]

UI

You need a center tapped secondary on the input transformer for it to work on a BA-6A. Look at the schematic.
The control voltage for a vari mu is sent to the center tap.
The BA-25 schematic does not show a center tap.

Thank you for letting me know! I just found the schematic for the ba-25 .

 

[Thegoldenlockedlamb]

The interstage primary is also shown with a center tap and is operating as a push-pull.
These are very special transformers to the design. Not common. Good thread here that addresses your question on many levels.
If you don't want to spend the amount $$$ needed for authentic (either vintage or sowter), some circuit redesign would allow more common transformers to be used. See DaveP's comment in the above link.

I may just have to pony up the cash. I checks and sowter isn’t as bad expensive as I originally thought . Do you think it would be better to alter the design and use more standard transformers ? I ask because I’ve always read you need an output pad for these to work with more common gear these days .

Thank you for your help.

 

[scott2000]

The output is 7k7:500

How's this one look?
https://www.ebay.com/itm/1447435745...17&osub=-1~1&crd=20230109084214&segname=11051

 

[dmp]

I may just have to pony up the cash. I checks and sowter isn’t as bad expensive as I originally thought . Do you think it would be better to alter the design and use more standard transformers ? I ask because I’ve always read you need an output pad for these to work with more common gear these days .

That's common with varimu since they need to develop a really high signal level to drive the sidechain. The schematic has an attenuator after the output transformer. Not related to changing the design to use off the shelf transformers, will still have a output level that needs an attenuator.

T1: look at ua175 to see workaround for CT secondary and use any 600:60k
T2: DaveP's suggestion to drive the interstage with cathode followers (adding a tube) to use any 10k:10k
T3: This transformer is possible to get, but possibly change to WCF (LA2A) to use a cheap Edcor 15k:600

It's a hard question. If you have a lot of experience with a BA-6A and know it does and sounds exactly like you want, then you should go all in on authentic. I'm still not sure there are any confirmed builds that the sowters can do the job right. Getting originals would take patience and $$$$$.
I expect there are nuances to the original circuit and iron that a modern version would lack (possibly in a good way). But I haven't used an original.
Modifying the circuit could bring down the cost a lot and maybe arrive at something really good.
A tube varimu is an advanced project, so expect it to be hard to build and get right. I would suggest you spend time to understand tube electronics and how the circuit works before attempting the build. Soldering it all together will be the easy part, debugging and calibrating will be the hard part.

 

[dmp]

I just found the schematic for the ba-25 .

The RCA section of the technical documents here is a good 1st place to look - save you some time
The manual is there that describes the operation - would help you a lot

 

[Rob Flinn]

Also aren’t you the guy who built the API style console a few years ago? If so that is a really awesome build !

Not me. I am an MCI console user.

 

[Rob Flinn]

I have a nearly finished Ba6a that I used a hammond 835 for the interstage which is 40k:40k. I've not yet passed audio through it, but itseems to behave nicely on my bench tests.

Other transformers I used are a Gardners 600:10k for the input. I can't remember what the output transformer is, but it could be a triad but from memory it is 8k:600

 

[Thegoldenlockedlamb]

Not me. I am an MCI console user.

Oh nice still cool , I used to own a 1979 mci jh536c that I stupidly sold When I lost my better job I used to have . What model mci do you have ?

 

[Rob Flinn]

Oh nice still cool , I used to own a 1979 mci jh536c that I stupidly sold When I lost my better job I used to have . What model mci do you have ?

JH428B which had VCA automation (quite unusual for a 400 series) long since disabled when the comnputer died like most 500's