Antek Transformers

[deiseldave]

Can someone explain a couple things about these transformers?
https://www.antekinc.com/content/AS-1T300.pdf
I don't understand why there are multiple primary and secondaries with the same values (2 x 115V primaries, 2 x 300v, 2 x 6.3V)
I have a couple of these in my parts box, and was wondering if they could be used for TW Express builds. Can the secondaries be paralleled for increased ampacity? Thanks.

[Phil_S]

Can the secondaries be paralleled for increased ampacity? Thanks.

Yes you can or you can power a second node independent of the first one.
The primary allows series connection for 230v primary and parallel connection for 115v. This allows for full capacity in either configuration.

[deiseldave]

Thanks Phil. Is the purple on the primary the earth?
Thanks again

[bmx]

Purple is "electrostatic" screen. It is a copper shield that capacitively shorts high frequency noise from the primary side of the winding to ground, as opposed to letting the high frequency noise couple from primary to secondary. So, yes! Connect Purple to ground. I have had good luck building with Antek transformers. Great tones, and nice and light

[deiseldave]

Thank you.

[brewdude]

I saw that Antelope is now selling toroidal output transformers.

Anyone know anything about toroidal output transformers?

[R.G.]

Toroids are more "perfect" in the technical sense than E-I transformers in most ways, but they have two big gotchas and one small one to avoid.

The first gotcha is price - they're more expensive, watt for watt, than E-I normal style transformers. Until modern special purpose winding machines were invented, a toroid was dramatically more expensive than an E-I. Now it's only moderately more expensive.

The second is magnetic saturation. The thing that makes toroids more "perfect" is their almost complete lack of an air gap in the core. Toroid cores are wound up from a long strip of iron into a donut. This lack of a clear air gap means that it takes fewer turns to make the primaries, so they can use less copper. But it also means that they are very sensitive to any DC offset on their primaries. This is mostly not a problem on AC mains toroids, but for an output transformer it's a big deal. Toroids are almost unusable for SE outputs, as SEs have to have a DC offset. And they are very touchy to use for push-pull outputs because the DC conditions on each side of the primary have to be very finely balanced to keep from saturating the core. This means that the biasing currents of both sides of a push-pull output stage have to not only be as equal as you can possibly get them, but also that if the bias drifts it can send the OT into saturation. So you need frequent rebiasing or something like a bias current servo.

The minor gotcha is that for OTs (but not AC mains applications) toroid windings may be more "perfect" to start, but they are less flexible to get right for good high frequency response than EI types. This is a bigger deal to hifi OTs than guitar OTs.

[xtian]

As far as expense, the model mentioned above is only $50. That's cheap!

Do you need specific hardware to bolt it to the chassis?

[deiseldave]

It comes with mounting hardware. A bolt, washer, nut, (2) rubber isolation disks and a metal disk to compress and hold in place.

[deiseldave]

I also bought a smaller one a while back that has a 260VAC secondary, with intentions of doing Martin Manning’s compact Dumbleator build. It looks like it’s going to fit in the case that Martin used. I may have to put some larger feet on the box to get past the bottom of the bolt.

[deiseldave]

This is The one I was planning on trying out for Martin’s Dumbleator later build.

https://www.antekinc.com/as-05t280-50va ... ansformer/

[mirage_indigo]

I just completed a Princeton BFR over in the Fender sub-board using an Antek. I used the as-05t320-50va-320v part + a solid state rectifier and got about 375V on the B+ when biased hot. I had never used one before, but so far it's working great. You can check out the schematic in the "Donut Princess" thread. The basic power supply should work on anything with a pair of medium output tubes up to 6L6GCs. Even at full out into an attenuator with a hot bias, the PT never gets more than slightly warm.

Note that Antek's website is kinda limited, so there's not much info available. I ended up using the heater windings in parallel (with Steve Luckey's help figuring out the phase), which gave a 6.3 V winding with double heater capacity. The windings are actually colored a little differently than labeled on the datasheet, but are labeled correctly on the part itself.

[T Wilcox]

This is The one I was planning on trying out for Martin’s Dumbleator later build.

https://www.antekinc.com/as-05t280-50va ... ansformer/

Ive used that tranny many times. I wanted to have another dumbleator so I added one to the back panel of Marshall style preamp I built recently.
I used the 240 on this one but think the dlator would be closer to spec with the 280 since my voltages were lower. I prefer that with the Marshall pre though and the dlator seems to work perfectly
They are great trannies. Thinking of trying out the PT and OT's they offer for a standalone power amp eventually

[Murrayatuptown]

Antek now has a few HiFi Toroidal OPT's.

On eBay, they have a setup that claims they have too much correspondence to respond to questions...which I didn't know was acceptable on eBay.

I occasionally have an e-mail conversation with Menno Vanderveen.

The last one started out about gapping of toroid cores & distributed gap concept. He is never discouraging (physicist & teacher), and gave me answers. Initially, I was interested in partial gapping (incompletely cutting the core) with a goal of building in more 'tolerance' to DC imbalance in a PP OPT. He felt a complete gap was essentially necessary because the trade-off with not cutting completely thru is that the core cross-sectional area at that point is reduced, worsening the potential for saturation.

I made two half cuts on opposite sides of a small (about 1" diameter) tape-wound toroid with a Dremel diamond cutting wheel to determine whether I could even do it. (Yes, ugly, handheld, as rigging a fixture would have delayed progress. The wheel is only about 0.023" thick but handheld resulted in a wider gap (crevice is more like it). I filled the gap with epoxy.

I had a response from the owner of a power transformer company that makes large electrical distribution transformers with distributed gaps and he said my concept was right on track if I am aware of what the effects of the reduced core area would be at the slice location. His response hinted at 'relativity'.

Since I would have a hard time controlling a partial cut, and attempting this on an already-wound transformer (assuming one that had space to gap, away from windings...I have only ever had one toroidal xfmr in my hand that did) is full of problems including not knowing how many turns are present, I decided to drop the idea until I reassemble my torn-down toroid winder (15-20 years on hold, so dropping the idea may be wise for faster answers).

I decided to consider 'how bad' DC flux might be for some assumed core, turns count and DC currents ..to explore some numeric values (the 'relative to what' question).

My scenario was to have current balance in the 1-2 mA DC range, for small output tubes. I did not calculate very large DC flux values. I wondered what was missing in my thinking.

Another e-mail to Menno, and he said my thinking was now in the right place. Other than his gapped SE toroid designs, he does not gap his PP toroid designs...it's a matter of determining what is tolerable. He said he usually has something on the order of 500 H primary inductance and has to choose how much unbalanced current is tolerable (to him). He does have a bias servo PCB (joint project with Guido Tent, if I understood correctly), but said the result of small DC imbalance is usually an increase in 2nd harmonic distortion...you decide if the warm valve sound is ok for your project...usually not a problem for guitar amps.

So core saturation from DC imbalance is not going to happen instantly and absolutely in every case. It may not be advisable for some situations but for small output tube PP amps and substantial enough cores, satisfactory results may be obtainable.

I don't think it's a good idea to just 'try it and see' for every random build and builder, but with reasonable effort, the urban legend of core saturation from (any) DC imbalance level can be manageable (relatively). Not everyone uses bias servos.

So, after I pay off my credit card (again), I plan on trying Antek's $50 10W 'hifi' 8k (?) primary OPT as well as a couple of their suitable turns-ratio toroidal PT's as OPT's. They don't answer such questions on their website either. I'm looking at roughly 1-5 W PP amps for my experiments, and may consider the 10W OPT (20-20000 Hz) for a guitar (>70 Hz) amp in the 10-15 W range later.

This gets me off the hook for reassembling the toroid winder for the time being, too.

Whenever people tell you you can't do something, they typically mean well, but often haven't tried it themselves or read it somewhere. So it just makes you find out for yourself...like finding the note that hasn't been wrote (I don't remember who said that...Thelonious Monk?), or finding the turn that hasn't been burned...