6S19 Circlotron (OTL)

[Fuling]

Hi,

Irrational as it might be, I´ve become interested in Circlotron amps lately. I have a big stash (40+) of 6S19 tubes, 20 noval sockets and some interesting power transformers (two 2x6V 50VA toroids for the heaters and four 68V 100VA EI transformers for the floating output stage rails).

Some questions:
Can an OTL circlotron output stage operate in class AB?

Would 95V rails be waaaaayyy to low (using 8 x 6S19 per channel*)?

Is a tube or a solder joint goes south, would it mean the end for my speakers?

* With 4x6S19/rail, ie 8/channel I should get a peak current capacity of about 1,2A which should give almost 6Wrms @ 8R.

[flg]

Originally posted by Fuling
Irrational as it might be, ...

I happened to have worked up a Circlotron design but it's mosfet I have a sim file so if you feel comfortable with answers from it, , The topology would not be exactly the same but I'll bet you'll get most of your answers...

Can an OTL circlotron output stage operate in class AB?

In the definition of AB, do we have some small Iq current and with signal one side goes to 0 current and the other 100% of the current? Then, I think yes, is the answer. For instance, my basic output circuit wil drive 8 ohm just fine up to about 22Vp(44p-p). It uses 2.5A Iq in each side. You can see the non linearities of each side in the sim display of current. At 22V out one side drops at the peak point from 2.5A (Iq) to about 1.25A while the other side increases to about 4A. Not very linear The resultant is 2.75A through the speaker (22V/8R=2.75A)... Well, if I were to use a 2 ohm speaker that would be 22V/2=11A But, lets see what the Sim display of current looks like under these conditions...
As one side of Circlotron lowers it's current it hits rock bottom. Not 0 (400uA) but in this post Zero. Current in the other half turns on to essentially the 11A the speaker wants. This is all subject to no power supply current limiting being reached. That sounds like class AB dosent it?

Would 95V rails be waaaaayyy to low (using 8 x 6S19 per channel*)?

Dunno

Is a tube or a solder joint goes south, would it mean the end for my speakers?

Well, I simulated with a 1M resistor in the source of one side and the output will swing to full voltage of only one polarity. 22V or so in my case. Dose not sound dangerous so far... So then I shorted drain to source I don't think any of my supplies could actually do it but, my simulator supply is peaking at 800+Amps Not the answer you wanted to here. Me either, believe me, 90%+ of the time a mosfet fails shorted Do tubes fail shorted often?
Well, theres my 2C

[Miles Prower]

Originally posted by Fuling
Irrational as it might be, I´ve become interested in Circlotron amps lately.

Yeah, me too.

I have a big stash (40+) of 6S19 tubes, 20 noval sockets and some interesting power transformers (two 2x6V 50VA toroids for the heaters and four 68V 100VA EI transformers for the floating output stage rails).

No idea what a 6S19 is, I did a preliminary design with 6AS7s. Dunnow if I'll actually do that, or use lateral MOSFETs instead. Many VTs per phase means mucho heater power.

Some questions:
Can an OTL circlotron output stage operate in class AB?

Absitively!

Is a tube or a solder joint goes south, would it mean the end for my speakers?

You should add a DC offset detection circuit regardless of whether you implement this with SS or HS. Without an OPT, speaker poofage is always a possibility.

[HollowState]

Any of you guys want the Atma-Sphere MA-1 diagram? (6AS7s) Email me.

Victor

[CarlyBoy]

Circlotrons are also interesting me lately, OTL or not. I'm sure it's common knowledge to most members here, but it was only last week that I became aware that Wiggins = Electro-Voice and that they marketed transformer-coupled circlotron amplifiers from 15-100W. Given that the output impedance is 1/4 of that used in push-pull, these should be awesome sounding amps. (Anyone have/heard any of these?)

I recently exchanged email with Robert Turnbull, operator of this site:

http://www.audiocraftworks.gr/gr/pag...circlohist.htm

in an attempt to verify the OPT impedance for the A30 (uses 6BG6G or 1614) as I was considering constructing from the design - well either that or Al Stewart's circlotron circuit (AudioXpress, May 2002).

Sooner or later I've gotta put together a transformer-coupled circlotron and an OTL. (So much time, so little money..)

Roky, I think the tube you're referring to might be more commonly known as a 6C19. From what I've read it's like half a 6AS7 (ie single section) but I don't know how the ratings compare.

Victor, I have the MA-1 circuit as well. Do you know how to go about adjusting the bias and balance pots?

[tubelab.com]

No idea what a 6S19 is

It is the Russian equivalent of a 7233 (not pin compatible) which is roughly half of a 6AS7. I bought 20 of these from an Ebay seller in the Ukraine. I have been experimenting with them for use in cathode followers at low plate voltages. For $2.50 USD each, I can experiment on these, 7233's are $10 EACH and much more fragile.

Would 95V rails be waaaaayyy to low

I don't think so. I did some experimenting to see how much I could crank through this little tube. The maximum steady state plate current spec is 140 mA. I can reach this with 50 volts on the plate and -1.6 volts on the grid. At a plate voltage of 75 volts (my chosen voltage) 285 mA of plate current can be reached at a grid voltage of -1 volts. The plate shows a very dim red color in a totally dark room at this 21 watt dissipation. At 95 volts on the plate, -1 volts on the grid gives 440 mA of plate current and a gright red glow! You should be able to run these guys in AB1 with a reasonable idle current and still hit 400 mA per tube on peaks without drawing grid current at 95 volts.

As a side note I saw my first tube instantly and violently shatter last night. It was one of the 6S19P's. I must admit that is was a totally dumb blonde mistake on my part that caused it though. I had been testing some Bendix rectifier tubes so I had the filament wires soldered to pins 3 and 6 of the 9 pin socket. All other connections were made with clip leads, which I removed. Without thinking I plugged a 6S19P into the socket and switched on the power supply. The tube instantly popped sending glass fragments all over the place. After using a lot of bad language, I figured it out. Pins 3 and 6 are both plate connections on the 6S19P. My old Fluke power supply probably cranked 10 to 20 amps into that dead short. The weakest link was the wire that goes through the glass from the pin. As the wire vaporized it must have built up some serious pressure inside the glass, causing violent destruction.

[HollowState]

Originally posted by CarlyBoy
(Anyone have/heard any of these?)

Victor, I have the MA-1 circuit as well. Do you know how to go about adjusting the bias and balance pots?

Recently I got to hear the Joule Electra Grand Marque 160 watt OTL that uses 6C33Cs at the home of a high end dealer who's a member of the NJ Audio Society I belong to. Man, are they nice...and expensive!
http://www.joule-electra.com/index2.htm

CarlyBoy,
I've never owned that MA-1 but would think that the DC balance is set to provide the least DC offset (differential) between the upper and lower sections as measured at the output. The bias adjustment sets the operating level of the output tubes since the driver is DC coupled to them. This level is 750 mA per side, or 125mA per tube.

[woody]

I have been thinking about using a few of those 6c19pi tubes
in a circlotron to. As you see I already have a few tubes mounted.
I already have the 4 transformers for the 4 floating power suplies.
I bought some 110-230v autoformers that i was able to convert to
110v to 130v transformers. One of these is in the picture.

[Milen]

6S19 Datasheet

max. anode current is about 140mA, written in another datasheet...

[Fuling]

Thanks guys for helping me out with some answers!!

(Just for clarification: I´m not Roky Erickson, this is Roky:
http://en.wikipedia.org/wiki/Roky_Erickson)

440mA at 95V on the plate is better than what I estimated by looking at the datasheet.
According to this Pout might end up much higher than expected.