RS124 Output Transformer

[Rob Flinn]

Which Edcor did you find was underspecced?

Sorry I can't remember & I'm away at the moment so unable to look through my box of transformers. It seemed to work ok but I remember reading somewhere that it wasn't rated well enough for the altec circuit. I think it might have been this one https://www.don-audio.com/Edcor-XSM15k-600 but it could have been the 10k:600

 

[igs]

Have not used it but the UTM3580 is listed on their site for 436/ 124 style builds

I confirm, the UTM3580 is dedicated to Altec style outputs.

 

[Rob Flinn]

I confirm, the UTM3580 is dedicated to Altec style outputs.

Can you comment on post 10 of this thread ? It may put people off buying your transformer in the future.

 

[igs]

I don't recommend it. Tried it in a very similar 6CG7 push pull output stage and got the characteristic lack of low end of an underspec'd transformer. I also ordered their gapped BA2 output transformer which wasn't great in the stock RCA circuit it's advertised for either.

In this case, the reason for the poor frequency response is unknown to me. It's possible that the transformer was connected incorrectly. I conducted some AudioPrecision measurements again today, and the response is absolutely flat from 20Hz to 20kHz (-3db @ 7Hz). Please find the attached chart (10k load and 600Ω load).
We also use these transformers in our Tubecores 3U, where the output is similar to that of Altec. The Tubecore also exhibits an impeccable frequency response.
It would be helpful if @jazzcrisis could contact me via PM so we can resolve this issue together. These kinds of posts can harm the UTM's reputation.

 

[thomasdf]

I don't recommend it. Tried it in a very similar 6CG7 push pull output stage and got the characteristic lack of low end of an underspec'd transformer. I also ordered their gapped BA2 output transformer which wasn't great in the stock RCA circuit it's advertised for either.

Did you end up replacing it with a more another output that gave a more pleasing / better result ?

I am in the process of gathering parts for a pair of RS 124, and decided that the Sowter were too expensive for me. But I went for another route than UTM because the 3580 is not a direct drop in replacement, not the same ratio and core material.

 

[igs]

UTM because the 3580 is not a direct drop in replacement, not the same ratio and core material.

The UTM3580 is a direct replacement for Sowter 9745 (10:1 or 5:1, Grain Oriented Silicon Iron).
Brian Sowter personally recommended the 9745 to me for modern Altec-style applications, which require a lower ratio for a higher output level. The original Altec is 12.4:1+1 while we use 10:1+1. In my opinion it works better.

 

[thomasdf]

9745 you mean ?

The other thing I can't figure out is the difference in the lams. Audio difference I mean. I'd need to A/B that.

and I am drifting off topic, but am I right assuming Z11 and M6 is the same steel material ?

 

[igs]

9745 you mean ?

Yes, 9745, sorry for a typo.

Z11 and M6 is the same steel material

Not the same but similar. Both are Grain Oriented Silicon Iron. I'm sure you won't hear the A/B difference.

 

[Murdock]

In this case, the reason for the poor frequency response is unknown to me. It's possible that the transformer was connected incorrectly. I conducted some AudioPrecision measurements again today, and the response is absolutely flat from 20Hz to 20kHz (-3db @ 7Hz). Please find the attached chart (10k load and 600Ω load).
We also use these transformers in our Tubecores 3U, where the output is similar to that of Altec. The Tubecore also exhibits an impeccable frequency response.
It would be helpful if @jazzcrisis could contact me via PM so we can resolve this issue together. These kinds of posts can harm the UTM's reputation.

What was the source impedance? That is a critical value to know.
Most signal generators have a rather low output impedance of maybe 50 Ohm. Some have the option of 600 ohm. But that would still be way to low. The RCA BA-2A for example has a plate impedance of about 10k-15k Ohm... A transformer which measures great with 50 ohm source does not automaticly measure great with 10k ohm source.

 

[jazzcrisis]

In this case, the reason for the poor frequency response is unknown to me. It's possible that the transformer was connected incorrectly. I conducted some AudioPrecision measurements again today, and the response is absolutely flat from 20Hz to 20kHz (-3db @ 7Hz). Please find the attached chart (10k load and 600Ω load).
We also use these transformers in our Tubecores 3U, where the output is similar to that of Altec. The Tubecore also exhibits an impeccable frequency response.
It would be helpful if @jazzcrisis could contact me via PM so we can resolve this issue together. These kinds of posts can harm the UTM's reputation.

Of course! Let me state that you have brought a very impressive product line to market in an affordable way, and beyond those two experiences, I have no complaints at all. I'll send you a message soon with details so that we can figure out what happened. If it was my error, I'd be happy to retract that statement.

 

[igs]

What was the source impedance?

Attached are the latest measurements displaying the performance of the UTM3580 transformer across various source impedances, ranging from 50Ω to 10kΩ, with a constant load of 600Ω. The data indicates that changes in source impedance have minimal impact on the frequency response of the transformer.