There's a couple if interesting points on the OTL/Circlotron - given the focus I've had on this recently.
The power supplies need to be floating - this means the output of the SMPS needs to be floating and that then allows both to be referenced in terms of the B+ but also the heaters - usually the heaters are referenced to the B+ for the circlotron but with a bit of 'risk adjustment' (ie protective circuits to remain within Vhk spec) the circlotron can be fed with just a single supply.
I terms of resonant tank, the concern I would have perhaps is the tuning of the cap vs the movement whilst floating.
Either way the architecture should be isolated including the voltage feedback - preferably differential.
My circlotron output stage shares a single heater supply. On the other hand my cascode front end has separate supplies for heaters referenced to +80V and -150V. to keep within the 100Vhk specification of the 12BH7A. Something that the original M60 doesn't suffer from with it's 6SN7s.
I'm trying to find a supply like this to provide 490vdc b+ for a 50s era Crown tube studio amp, the SXA... IT HAS TWO POWER TRANSFORMERS... but they jumped them together to get the collective 490V. B plus. The individual Transformers put out about 365 AC... so I'm looking to get the extra 125 VDC... And if it's not too complicated, also get the preamp output voltage and filament voltages, since they might as well all be dc. Since i'm not doing a huge jump on the voltage, would there be something already may? Do you think?
Cool! Yes, actually it's pretty much laid out already like a dual mono block, and basically it wasn’t until i started rebuilding it, did it occur to me that the unit could exist that way, and it being Crown, i kind of wanted to know why they hadn't done that originally, which i had surmised would have been cost considerations, space condiderations, etc, and thats been borne out by all I've talked to. That really hip firm up in Canada that makes solid state power supplies for tube rigs told me since i wrote this that 100% those transformers will do the job separately, and then questioned my skills for even asking, lol. I just said that i realized the potential was there, obviously, because mathematically we are dealing with the same potential as dual monos in the same chassis, but i was concerned that the 490 b+ was required as a voltage, noting that there is some point in which the tubes won't perform, when the voltage to current ratio gets too lopsided. And i don't really know anything about EL37 tubes! Lol. But i have new multi-cell caps for both sides, and new individual bias supplies, and the #47 bulbs on each channel pretty much helps you nail the bias when adjusting and prevent tube damage. He sugested grid stoppers, which i had already planned on and a few other things. You can see in the pic here that the thing is laid out very symmetrically, with identical components on both sides... aside from the extra rectifiers ill have to build, but i akready bought extra caps snd stand offs to avcomplish these extras, just have to maybe redesign the look a bit to make 100% mirrored symmetry (on the under side).
Nice project!
Just check the spacing between the PSU capacitors (below the chassis, where you connect the wires) and the chassis. You don’t want any sparks there! Same with the diodes on the right of your picture.
Regards, Gerrit
Just check the spacing between the PSU capacitors (below the chassis, where you connect the wires) and the chassis. You don’t want any sparks there! Same with the diodes on the right of your picture.
Regards, Gerrit
Yeah, I already widened the holes for the original multi cell capacitors. I'm basically using the same standoffs that they used for the original system. But yeah, they need to be carefully done. I think it's going to be actually easier just to do this as a dual mono. I think all of my power problems that I had before this were because of bad bias, pots and parasitic leakage in other parts of the circuit. I was getting a strange 120 hum... it seemed to be coming from nowhere and everywhere, which is probably true. So everything going into it now is brand new. And i've got the benefit of a lot of other projects similar to this glean, things from. I thought my original idea was correct.And it seems like it is, so that's a good thing!
Oh, and since these are newer multi cell caps, i installed some holders from a Teac tape deck, so they can't get bumped. I'll likely line the routed out holes with some neoprene washers as well, provided I can attach them adequately. They'll also dampen the chassis, though I don't think this circuit is high-gain enough to have much in the way of microphonics, it certainly has the voltage. That much voltage can cause induction in things that wouldn't be an issue, normally. Obviously, there were some decent minds working at crown, even back then. But replacing everything down at the transformers, it seems to be the only way it's gonna be something more than it was originally.
I've been doing all my testing with 6L6 tubes. When I think it's safe enough, I'll put the EL37s in.
I've been doing all my testing with 6L6 tubes. When I think it's safe enough, I'll put the EL37s in.