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Toroidal transformer on tube amp

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Why are toroids so well regarded in solid state amps, but barely seldom seen on tube amplifiers? They are said to send less EMI and interference to sorrounding components, and some other good features.
Is there any reasong to be "so good" on solid state designs, but not in tube amplifiers? What about using them as output transformers?

I have NEVER used EI transformers, always sticked on toroidals. But I have never made a tube amplifier, anyway.

Thank you guys,
Regards
 
Conservative, in what sense? In using a 200W rated trafo for a 50w amp? Or conservative in the sense "I love stuff from 50 years ago"?

Maybe it worths to order a custom made toroidal, will think about that.

Coming from the SS world, I see that almost all tube amplifiers follow the same aesthetic designs rules. It may happen as well in the SS world, but coming from there, I am unable to notice :D
Builders use to have trafos and tubes exposed out there, without any covering. I wouldn't even think about having those hot (both electrically and termally) devices exposed to anyone who may come by and touch them by accident. That includes me and similar pets. Why not just cover them with a cheap bird cage of the proper size and adapted? That should mantain visibility for aesthetic reasons, and allows heat to be radiated and dissipated.
 
Commonly SS amps are not using signal trafos. So saying SS favors toroid cores we better reverb as PS trafos favor toroid ones.

Signal trafos (or "tubes") implementing sophisticatedly sectioned windings very hard to perform in case of toroid form-factor. And once all trafos including big and heavy OT are not toroid core’s ones it might make sense implement PS trafo with a similar no-toroid core design.

Double C (U) core seems to be the right approach. Plitron makes toroid audio
Audio Output Transformers | Plitron
 
The toroids for power xfmrs usually send out less magnetic interference if they are made right. (the section near where the wires come out can be a problem if the windings don't cover 100% of the core there).

But the power toroids send a great deal more conducted electrical noise thru themseleves from the power line to the secondaries due to their high primary to secondary capacitance and low leakage inductance (unless internal shielding is incorporated, not common on toroids though). The E-I power types for tube gear have low capacitance primary to secondary, and almost always have a grounded shield layer in between. The higher leakage inductance helps isolation too.

For output xfmrs (OT), the toroid versions are more difficult to make due to the high turns count and the high distributed capacitance. Special (expensive) winding techniques are required. And HV isolation (low capacitance) between the primary ends while maintaining close magnetic coupling is difficult. One can get most of the magnetic advantages of the toroid (low leakage inductance)by using cut cores or long E cores which are easier to wind.
 
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I have posted several times regarding this subject. Despite certain difficulties, toroids are really worth trying.

This is my draft build of push-pull amp using all-toroid design.
 

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I do have a web page with pictures and some schematics but it needs some repair. I will fix it and let you know. Mine did not win because a screw had loosened on the drive down to our meeting place and a channel was not working. At a subsequent meet, it sounded better and more powerful than another of the contestants.

ray
 
Primary 230v, secondary 33-0-33 v, 200VA

I have bought a couple of these transformers, and they appear to be good quality.

I have been considering if they are sufficiently flexible in the way they could be used, if it was worth getting a couple more for the 'parts bin'.

  1. They could be linked back to back, to get 230v isolated, and piggy back of the linked 33-0-33 secondaries to feed heaters.
    (Question: How best to link the secondaries? Treat them as 0-66V, and do not attach the CT?)
  2. I could try and use one with a voltage doubler. That should get me to 180V, I was hoping. Would this be enough for a PP EL86 amplifier? (A = G2 = 170v)
  3. I could use them in series, primaries connected in parallel, so I'd get 66-33-0-33-66 400VA.
  4. I like the idea of using power supply toroids as output transformers, but I don't think these voltages are much use. If I had 8ohm speakers, and a PP output stage (centre tap to B+), then I am looking at (230*230)/(33*33) * 8, which is just 388 ohm raa, and not useful, as far as I know.

The original idea was to try and build the simple valve tester on the Valve Wizard site ...
The Valve Wizard
... and I think with my mains (235v) and basic bridge rectifier with a 100uf cap, the 100v should be OK.

How useful are they?
 
Antek makes toroidal transformer for tube amps. I think that the reason we are not seeing more toroids in tube amps is due to the fact that not many are available on the market. Besides Antek, the other brands that I have seen were a lot more expansive than hammond or edcor, so that might be keeping people from diving into this. On the other hand, antek transformer are affordable and available in many different power ratings and secondary voltages. All of their high voltage transformers have 6.3V secondaries with good current ratings. I seriously considered them for my tubelab sse, but found a good deal on used allied 6k7vg...

AnTek Products Corp
 
In a regular circuit, I totally agree with you. But mains transformers have been successfully used as output transformers. Have a look at this design :

Return of the Darling

Let me specify: None of the power transformer they make for tube amps are suitable.

They make other power transformers that will work though. Personally, I use Triad since I'm in Canada, and AnTek want's a fortune for shipping.

I'm using a pair in series connection for my monoblocs. I get full power (112W) at 30 Hz this way.

I remember Plitron making toroid OPTs, but that they were expensive.
I can't reach their website right now, so can't check.

In Europe, these guys make:
Tube output transformers - Shop Toroidy.pl

Plitron was in Toronto, and I think they have ceased production.
 

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