neat Toroidal power tf's- Antek Inc.

[Robert M. Martinelli]

Hi Enzo,
Why not?
If the rubber disk keeps the bolt insulated on one side then the bolt has no way to close the circuit and become a sort of shorted turn....

( Better still would be to get a plastic bolt & nut )

Regards

Bob

[Steve Conner]

Gregg, if there are two identical HT windings, they're presumably intended to be used in series with a FWCT tube rectifier, or in parallel for a bridge rectifier. (Or even in series with a bridge rectifier, for uber voltage.) You won't get the full rated performance if you leave one of them disconnected.

Toroidal transformers don't leak much flux at all, but I sometimes see them inside a copper or iron canister in really hum-critical applications, like posh Linn phono preamps. When it comes to OTs, maybe the core is air-gapped, which makes it leak a lot more. Or maybe they canned it for looks.

The rubber pads that ship with toroidal transformers are mainly to stop the windings being crushed by the clamping force. They don't stop the single turn effect: the top of the mounting bolt, and the metal pie plate clamp thingy, are still hot compared to the bottom. If you can call half a volt "hot"... You can actually measure it with a DMM set to AC volts though: put one prod on the chassis and the other on the pie plate. Bigger transformers make more voltage.

Bob's comment on the wadcutter reminds me of something I read on the Darwin Awards website. According to the story, a guy was doing some car repairs, and needed to drill a hole in his muffler for some reason. He decided not to use an ordinary drill, but to shoot a hole in it with a handgun instead. The bullet ricocheted off and hit him in the leg. (Enzo, bear this in mind next time you need to "fix" a Marshall Mode Four )

[Robert M. Martinelli]

Hi Steve,
that' s the reason why I clearly specified to use a wad, even if wad-cutters are low-velocity-target-bullets and they aren't likely to ricochet, I don't want someone to hurt himself or to win a Darwin Award in my place - that prize has to be mine and only mine!

Getting serious,
I remember a ( non-enthusiastic ) comment of yours about toroidal transformers used as OTs, I see this guy has them in his catalog, can you elaborate on that?

As to the rubber pad, I know it won't stop the bolt from becoming a "turn", but it insulates the bolt on one side keeping it from "shorting".

Regards

Bob

[Steve Conner]

Hi Bob,

My personal feeling on toroidal OTs is that they're probably too hi-fi for guitar use, and don't tolerate mismatched power tubes at all well. I've never owned one though: I formed this opinion from experiments that I did putting audio and test waveforms through toroidal PTs and measuring their saturation curves.

At those Antek prices though, it may well be time to buy one and see The last time I tried to buy a toroidal OT, it was a General Radio 100w unit that ended up going for $400 on Ebay.

[Enzo]

Not to belabor it, but I do so love a discussion of tiny details.


Bob, the bolt thing has nothing to do with it touching the transformer. The bolt just passes straight through the center hole, not touching anything. But since the bolt is through the bottom of the metal chassis, and that netal floor is bent up to form the walls, and then a top sheet is screwed to the sides. If that top sheet touches the other end of that bolt, all that metal - bolt, chassis, and cover - form the metal turn around the torus. Nylon hardware of course cures this. Making sure your metal bolt is short enough does too.

Unless I misunderstand, the rubber cushioning washer won't insulate the bolt from the chassis.

[Robert M. Martinelli]

Ok Enzo, I got the picture, I understand the bolt has to "close" the turn ( it acts like the inner part of the "winding" while the metal chassis around acts like the outer part ). I would then keep the rubber disc to protect the transformer mechanically and use plastic bolts and nuts ( or keep the bolt and the nut isolated on both sides ) to secure it to the chassis.
Thanks
Regards
Bob

[Gregg]

Gregg, if there are two identical HT windings, they're presumably intended to be used in series with a FWCT tube rectifier, or in parallel for a bridge rectifier.

I know that but still I don't think this is a good idea. Moreover there's no 5V winding and you'll have to use one of the 6V windings and adjust voltage.
According to Plitron there are some issues when using a toroid with a CT FW recto:

http://plitron.com/technotes.asp

I'm using toroids with bridge rectifiers from a long time and I'm happy with that.
As far as fixing the transformer to chassis the ones that order come with two 2mm rubber rings and a metal plate. One ringe goes between transformer bottom and chassis, the other /smaller/ one goes on top, then the special metal plate on top of. This way the chances to have a short are close to zero:

[Amp Kat]

I used a Teflon bolt for my Slo Clone and it worked great. This was a Plitron transformer designed by Menno Van Der Veen and as mentioned I had to use a FW rectifier but it worked very nice and delivered very low noise application for that amp.I have a shot somewheres I'll try to find on the other computer of that bolt.

[Ptron]

Instead of the not needed second high voltage winding they could have included a bias voltage winding thus decreasing the size even more.

I'm with you on that. Isn't 400mA way overkill for a typical 100W amp as it is? (And isn't 6A of heater current on the low side to support a 100W tube compliment?) Why not offer a smaller one with just the single winding for 50W amps? A bias winding would sure be handy. Especially for those who like to use it as a switching supply.

The prices are really good - the lowest on toroids I've seen so far. The only explanation for that is obvious but not necessarily a bad thing.

They're cheaply made? They make them in quantity? They're trying to get their foot in the door? I guess it isn't that obvious to me .

[imaradiostar]

Well...I've ordered two. I spoke incorrectly before. I ordered an AN-1T200 and a AN-1T300.

I think that (from the specs anyway) these things have way lower core and copper losses than we're used to seeing. This should mean better voltage regulation and more power if I understand things correctly.

The real proof will be using them. I'll report back!!

jamie

[Gregg]

They're cheaply made? They make them in quantity? They're trying to get their foot in the door? I guess it isn't that obvious to me

Well, we all know where things are made in big quantities for less but that doesn't mean they are made cheaply.

The real proof will be using them.

I agree on this. Until "field tests" with the brand in question are performed we wouldn't know.

[R.G.]

One other caution based on micro-details: toroidals are EXCRUCIATINGLY sensitive to DC offset on the AC power line.

One hifi enthusiast with toroidal powered amps found that his beloved setup hummed at night but not in the daytime. No amount of troubleshooting could find the problem. One day he was looking for it about twilight when his outdoor lights came on. Ding! The hum started.

He finally found that he had put some of the half-power wafers in his garage outdoor lights. These are diodes which half-wave rectify the AC power line into the light bulb and cause it to glow less and last a much longer life. It also offset the house's AC power line by a fraction of a volt on a DC basis and causes the toroidals to saturate a bit on one side and emit hum radiation.

Yet another hum gremlin loose in the world...

[Enzo]

Wow. Now THAT is esoteric. I love that shit.

[Steve Conner]

Yeah, that's pretty trivia-tastic.

It also helps you to imagine what a DC offset due to mismatched power tubes might do to a toroidal OT. It'll sound like poop and your garage lights will go dim every time you hit a power chord.

[imaradiostar]

It's been a while since I replied to this thread. I thought I should at least chime in and let you know my results so far.

I hooked up a AN-1T300 in one of my ongoing amp projects. I have a Bogen 35 chassis that's been so many things over the years that I've lost count. Right now it has an EF86 input with a 12ax7 LTPI (vox values) and a pair of new production 7591a's. I'm using a Triode Elec ultralinear Deluxe reverb output tf (the inexpensive one). I've been using it to play gigs at church and lent it to friends and results have been positive.

The B+ voltage was a little lower than I was hoping for but I used the extra winding on the PT to bump it up a bit. Though the data sheet says it has two 6 volt windings both PT's that I purchased ended up with a 6 volt and a 12 volt winding. I connected the 300 volt windings in parallel then wired the 12 volt secondary in series to increase the voltage going to the bridge rectifier. This gives me a plate voltage a little over 410 volts under 100ma load.

So...this is off the top of my head so don't quote me on the voltages and currents. I have the output section setup back-biased with a 220 ohm resistor to ground. The input cap from the 4x1n4007 bridge rect is a pair of 160uf 330 volt photo-flash caps in series with 220k resistors across each. The following filter stages are a 22k dropping resistor into a 80uf 400 volt cap and a 10k into another 100uf? cap mounted on the terminal strip next to the ef86.

I'm pretty sure I have the bias pot dialed fully negative (meaning coldest possible bias) and the two 7591's are drawing about 92ma through a precision 1 ohm resistor. This puts them at about 100% static dissipation. I know it's wrong but it doesn't get too hot, doesn't blow up and it sounds good. It's usually used at uncomfortable volume with a THD Hotplate to knock it down to usable volume- typically the -8 or -12 dB positions. The amp sounds tight and focused through a closed back 2x12 with a Greenback and G12-75. Bass response is decent without being flubby- pretty neat!

The B+ power sags very little under load and the 6 volt line is still above 6.3 volts under load. After repeatedly power soaking it and trying to get it hot the power TF never gets more than a little warm. I have a feeling this PT could comfortably handle a lower voltage EL34 amp without trouble- maybe a Trainwreck or Matchless type amp.

I'm planning to retire this amp as an "experimenter's chassis" after this build. It's been so many different things over the last 15 years. I think it's time for it to get a nice wood cabinet and a professionally made faceplate that says "Dr Bogen." (hint hint) The only other thing I may do is convert it to more Bogen like status- go back to the Bogen output tf, original fixed bias 7868's (I still have them and they test well on my tube tester) and convert from an EF86 input to a cascoded 6eu7 or 12ax7 input. The idea is to build something that could be built from a Bogen chassis with minimal effort. The cascoded input should be more tolerant if I decide to put it into a combo cabinet- probably with a pair of CTS 10" speakers rescued from Shure "vocal disaster" monitors I took apart a few years back.

Sounds like it's still a project.

Two thumbs up on the toroids! I'll let you know how the home stereo amp build goes.

jamie