[Tjj226 Angel]

So, if I go this route - I would need 1 toroid for power and 2nd toroid serving as the SET transformer? (i.e. abandoning OTL architecture)
...and this would be quite noisy amp (due to toroid capacitance)?

You wouldn't have very good high frequency performance if you used a toroid transformer on the output of the amp due to interwinding capacitance.

Toroid - power supply = Good.

Toroid - output transformer = probably bad unless you find yourself a transformer winding wizard or something.

 

[L0rdGwyn]

It's also worth adding to this that no one has cracked the code on how to make really high quality audio toroid transformers quite yet. Their interwinding capacitance is usually huge compared to a cheap EI transformer.

I know Toroidy makes single-ended output transformers, although I have read little-to-nothing about them. Here is their 300B single-ended offering.

https://sklep.toroidy.pl/en_US/p/TTG-EL34SE-Tube-output-UL-transformer-3,2kOhm-EL34-6L6-SE/560

So, if I go this route - I would need 1 toroid for power and 2nd toroid serving as the SET transformer? (i.e. abandoning OTL architecture)
...and this would be quite noisy amp (due to toroid capacitance)?

You would need a pair of output transformers for a SET design. The issue with the capacitance is the RC formed by the output tube plate resistance and the interwinding capacitance of the output transformer, which will roll off the high frequencies.

 

[Tjj226 Angel]

I know Toroidy makes single-ended output transformers, although I have read little-to-nothing about them. Here is their 300B single-ended offering.

https://sklep.toroidy.pl/en_US/p/TTG-EL34SE-Tube-output-UL-transformer-3,2kOhm-EL34-6L6-SE/560



You would need a pair of output transformers for a SET design. The issue with the capacitance is the RC formed by the output tube plate resistance and the interwinding capacitance of the output transformer, which will roll off the high frequencies.

I know. Look carefully at their capacitance spec for their lowest impedance transformer. It is still 7.6nf. For a 3K transformer, we really want to be down in the 2nf range and below.

At 7.6nf, the capacitance becomes a problem somewhere in the midrange.

This is part of the reason why transformers get so expensive. In order to achieve really good high frequency performance, you have to wind a bunch of individual coils on the bobbin and put them all in series. All the individual coil capacitances and inductances are put in series as a result. When you put inductance in series, it adds (good thing). And when you put capacitances in series, it gets smaller too (also good thing).

Usually the better built transformers will have alternative winding layers, but toroids (for what ever reason) apparently can't have a lot of layers in series or something? I know there is an article out there that explains all of this.

 

[L0rdGwyn]

Well, since the mail ran so late, wasn't realistic to finish the 45 amplifier tonight, unless I were to stay up until 2AM.

So I will be up at the crack of dawn to finish the job. Here is how far I got on the interior.

 

[bcowen]

Well, since the mail ran so late, wasn't realistic to finish the 45 amplifier tonight, unless I were to stay up until 2AM.

So I will be up at the crack of dawn to finish the job. Here is how far I got on the interior.

MMMMMMM....oil caps and Rikens. I can tell it's going to sound great before you even finish it.

 

[L0rdGwyn]

MMMMMMM....oil caps and Rikens. I can tell it's going to sound great before you even finish it.

Wait until you see the parafeed caps, they are freakin' huge! I was a real psycho when I built this amp the first time and even used Rikens as the current set resistors on the four CCS boards LOL. Well they're already there so they're staying.

The color turned out really well, going to look pretty classy I think.

 

[A2029]

I know. Look carefully at their capacitance spec for their lowest impedance transformer. It is still 7.6nf. For a 3K transformer, we really want to be down in the 2nf range and below.

At 7.6nf, the capacitance becomes a problem somewhere in the midrange.

This is part of the reason why transformers get so expensive. In order to achieve really good high frequency performance, you have to wind a bunch of individual coils on the bobbin and put them all in series. All the individual coil capacitances and inductances are put in series as a result. When you put inductance in series, it adds (good thing). And when you put capacitances in series, it gets smaller too (also good thing).

Usually the better built transformers will have alternative winding layers, but toroids (for what ever reason) apparently can't have a lot of layers in series or something? I know there is an article out there that explains all of this.

I got some Toroidy transformers custom made to test out for an amp that I've had sitting on a shelf for the past while. Told them that I'd like it to be -1dB or better at 20Khz, so I look forward to testing to see if they were able to do it. They didn't provide any specs with the transformers as it was a custom job. Guess we'll see

 

[Zachik]

I got some Toroidy transformers custom made to test out for an amp that I've had sitting on a shelf for the past while. Told them that I'd like it to be -1dB or better at 20Khz, so I look forward to testing to see if they were able to do it. They didn't provide any specs with the transformers as it was a custom job. Guess we'll see

What kind of amp is it for Mischa?

 

[Tjj226 Angel]

I got some Toroidy transformers custom made to test out for an amp that I've had sitting on a shelf for the past while. Told them that I'd like it to be -1dB or better at 20Khz, so I look forward to testing to see if they were able to do it. They didn't provide any specs with the transformers as it was a custom job. Guess we'll see

Frequency response is one thing. I would be more curious about the phase response out to 20Khz.

I really do hope they work though. I have been eyeing the GM70 output transformers.

 

[A2029]

What kind of amp is it for Mischa?

It's a parallel KT150 single ended amp for my personal uses. 12BY7/12HL7/12HG7 driver into the KT150s. I went way overboard with polishing on it due to OCD. I even set up a rig for electropolishing the stainless steel chassis. Sides made from African Padauk wood. The whole amp is kind of an experiment in going overboard, lol. >3000uF in the high voltage supply running over 600 volts Remote control stepped relay attenuation with programmed soft start... I'll post more on it when I have it completed and up and running.

Toroidal transformers are traditionally very poor performers when used in single ended applications as they saturate very easily when there is a DC bias present. To get around this, I believe Toroidy and some other Toroidal audio manufacturers are using powdered cores that have some inherent gap for running DC bias, but they are still not very popular on the market, and reviews are almost non-existent, so will be very interesting to hear and measure their performance.

 

[A2029]

Frequency response is one thing. I would be more curious about the phase response out to 20Khz.

I really do hope they work though. I have been eyeing the GM70 output transformers.

I really hope so as well! Luckily the experiment with them isn't too pricey, and they would represent pretty good value if they work out well and sound good. I'll definitely be posting my findings.

To extend their bandwidth I'm also thinking of trying to semi-float their secondary using a resistor in tandem with some protection circuitry that would trigger if there was a short between the primary and secondary, shunt the HV supply current to ground, and shut down the amp. Wouldn't want 500+ volts on a speaker cable. Will have to think about how best to do this.

 

[L0rdGwyn]

It's a parallel KT150 single ended amp for my personal uses. 12BY7/12HL7/12HG7 driver into the KT150s. I went way overboard with polishing on it due to OCD. I even set up a rig for electropolishing the stainless steel chassis. Sides made from African Padauk wood. The whole amp is kind of an experiment in going overboard, lol. >3000uF in the high voltage supply running over 600 volts Remote control stepped relay attenuation with programmed soft start... I'll post more on it when I have it completed and up and running.

Toroidal transformers are traditionally very poor performers when used in single ended applications as they saturate very easily when there is a DC bias present. To get around this, I believe Toroidy and some other Toroidal audio manufacturers are using powdered cores that have some inherent gap for running DC bias, but they are still not very popular on the market, and reviews are almost non-existent, so will be very interesting to hear and measure their performance.

I remember you mentioning this amp, can't wait to see it. Did you get those sweet chromed transformer shields from Toroidy too?

 

[Zachik]

I went way overboard with polishing on it due to OCD. I even set up a rig for electropolishing the stainless steel chassis.

Yeah... That is the reason I prefer matte finish...

 

[A2029]

I remember you mentioning this amp, can't wait to see it. Did you get those sweet chromed transformer shields from Toroidy too?

I opted for the cheapo non-potted versions, there was enough polished stainless and polished aluminum film caps for my liking already

 

[L0rdGwyn]

Okay the 45 parafeed rebuild is done, finally. Always takes longer than I think it will.

Here is the circuit first, there is a lot crammed inside.



Top.



Rear panel. Speaker binding posts sit behind the output transformers. Rear switch is for the headphone output.



Here it is with some tubes.



Bottom plate is perforated aluminum sheet for ventilation.



I like how compact this amp is, small footprint considering how much stuff is stuffed inside. It sounds great, spinning some vinyl.



Will have to go back in at some point to finely dial in the filament supply and I may better match the 45 CCS FETs, but overall it's done, I can mark it off the list! Will probably take some measurements later today.

841 amplifier is next...