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.

 

[MediaWorksOKC]

Were there any further thoughts on the issues experienced, any realizations or resolutions? I see Igor is unable to reproduce such an error.

I have an interest in the same conditions under discussion for an output transformer in several similar circuits and would prefer to support Igor and UTM with the business ultimately.

-Chris

 

[rock soderstrom]

Were there any further thoughts on the issues experienced, any realizations or resolutions? I see Igor is unable to reproduce such an error.

That would also interest me, as doubts have been sown here without reliable technical data and without naming the exact purpose of use.

Igor, on the other hand, has delivered(!) and I personally think that if the problems mentioned really existed, the manufacturer would fix them by optimizing the product in question, right?

 

[Murdock]

That definitely won't handle the power level cleanly and I doubt it handles the current, DC resistance is high meaning small gauge wire.

I still don't understand how one can know/calculate how much current a PP transformer can handle... the push pull stage cancels the DC current but the windings still have to be able to handle it?
Let's take the RS124 for example. The output stage draws about 15mA, so 7.5mA per tube, right?
That means if we have an output transformer like the Hammond 850LA, one winding (760 Ohms) dissipates 0.04 Watts. And that would be too much?

What is the max current a Triad HS52 can take? On the case it states 12.5mA. Is that the max unbalanced DC? Is that per side or for the whole transformer?

 

[emrr]

I still don't understand how one can know/calculate how much current a PP transformer can handle... the push pull stage cancels the DC current but the windings still have to be able to handle it?
Let's take the RS124 for example. The output stage draws about 15mA, so 7.5mA per tube, right?
That means if we have an output transformer like the Hammond 850LA, one winding (760 Ohms) dissipates 0.04 Watts. And that would be too much?

What is the max current a Triad HS52 can take? On the case it states 12.5mA. Is that the max unbalanced DC? Is that per side or for the whole transformer?

My quoted bit is mainly about the level handling of the 850L - less than the operating level of a 426. I recall they stated 0mA with no mention of balanced or unbalanced, suggesting at least that any imbalance at all will affect ratings.

Hs52 - 12.5/25mA - 25mA at 5K is clearly SE from the way it’s connected. You can’t get DC through it any other way.

 

[Murdock]

My quoted bit is mainly about the level handling of the 850L - less than the operating level of a 426. I recall they stated 0mA with no mention of balanced or unbalanced, suggesting at least that any imbalance at all will affect ratings.

Hs52 - 12.5/25mA - 25mA at 5K is clearly SE from the way it’s connected. You can’t get DC through it any other way.

Thanks. But do you know if the 12.5mA is the max current for both halves together, so 6ma each tube in push pull? Or 12.5mA per side?
Do you know the output current in the Fairchild 660/670 signal stage?