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Old 31st July 2010, 08:06 PM   #11
ilimzn is offline ilimzn  Croatia
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Quote:
Originally Posted by Yvesm View Post
Hi banat,
We don't speak about the same problem !
"Nanofarads" that usually appears between secondary windings of the same transformer are not hidden by any rectifiers unless you put a choke in serie with BOTH wires.
Of course, individual transfos improve the situation.
But I agree with the utility/necessity of some snubbers blocks.
Yves.
Still, interesting thought - full wave bridge rectifier, the actual transformer secondary is only 'connected' to the filter caps in the peaks of the secondary voltage waveform (conduction angle depending on current draw). If two such supplies were used for a circlotron, the secondary transformer windings see variable capacitance based on an intermodulation of the mains waveform and the output from the amplifier - in the peaks of the mains waveform, it's practically the true capacitance between windings/ground, whereas in other parts of the mains waveform these capacitances get charged and discharged through the various diodes. It seems to me that this would inject a rather hard to define portion of intermodulation products into the output - perhaps not overly significant if the capacitances between windings were kept low.

An alternative solution would be a pair of center-tapped windings with two diodes each for full wave rectification. Because each of the center taps represents one balanced output of the circlotron amp, the independent secondaries are always connected to the output signal and the capacitances may be much better defined, in particular if some care is taken to add electrostatic screening between windings.

Finally, a split bobbin or even better C-core or R-core transformer with electrostatic shielding may be used to completely separate the two windings physically. This way the capacitances the amp output sees would largely be towards the ground center point, a nice thick cardboard or similar separator can make these quite small, indeed.
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Old 31st July 2010, 08:52 PM   #12
banat is offline banat  Serbia
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Actually old split bobbin tehnique is always the best way to made Circlotron OPT(EI or C core trans or autotrans).This tehnique which is not complicate achive next:keep both OPT primary impedance,resistance,capacitance same,and keep betwen primary bobin kapacitance low.All The Best Ilimzn

Last edited by banat; 31st July 2010 at 08:56 PM.
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Old 31st July 2010, 10:16 PM   #13
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Quote:
I think I would prefer to just use a pair of KT88s with a transformer.
Something in this style?

http://www.wdav.de/1961-1964/PPP_Amp_Schaltbild.PDF
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Old 1st August 2010, 07:50 PM   #14
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Originally Posted by SpreadSpectrum View Post
Surely a tube OTL circlotron would require banks of power tubes to get a low zout. Are you saying it is possible with a pair of output tubes? That must require an unholy amount of feedback?

I think I would prefer to just use a pair of KT88s with a transformer.
Any hollow state OTL is going to require a lot of finals in order to move the bigamps through the speeks. (Unless you can get those special, Hi-Z speeks originally designed for hollow state OTL use.) A pair of power MOSFETs can do that with ease, but VTs are not low voltage, high current devices.

I've looked at a whole bunch of possible types for finals, but those 6AS7 dual triodes always look the best. Since you get two triodes with each bottle, that's half the holes you need to make in the chassis.
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Old 3rd August 2010, 12:00 PM   #15
banat is offline banat  Serbia
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Quote:
Originally Posted by revintage View Post
Here is OPT(autotrafo) for that Circlotron Amp,Rkk-900 ohm,Split bobbin coil.Best Regard
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Old 3rd August 2010, 07:40 PM   #16
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Quote:
Originally Posted by SpreadSpectrum View Post
Surely a tube OTL circlotron would require banks of power tubes to get a low zout. Are you saying it is possible with a pair of output tubes? That must require an unholy amount of feedback?

I think I would prefer to just use a pair of KT88s with a transformer.
Feedback is up to you- you don't need a lot to make a practical OTL, even if its low power.

These days, if sonic performance is your goal, there really is no good argument for 4 ohms, as nearly all transistor amps (as well as tubes) sound better (for different reasons) on higher impedances: 8 or 16. OTOH if sound pressure is your goal and you have a transistor amp, 4 ohms can be more desirable. Although this would seem intuitive, I have found that many people confuse 'sound pressure' with sonic merit...

If you can run a 16 ohm load 4 6AS7G power tubes will get you about 35-40 watts. Higher impedance loads will cause the output section to run at a lower temperature as less power is dissipated in the tubes. Distortion will be lower too. But even with 4 power tubes, there is no call for a speaker load over 60 ohms; I've used 4 8 ohm speakers in series for 32 ohms and gotten a very clean 55 watts out of 4 power tubes, although to take advantage of the higher impedance load I boosted the B+ on the power tubes to nearly 200V (obviously the amp was not class A either).

IOW there is a lot of flexibility once you get your head around the idea that it is possible, practical and reliable.
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Old 29th August 2011, 01:50 PM   #17
tinitus is offline tinitus  Europe
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have PP 1.6kohm output trafos

I figured circlotron might work

15watt would be ok
how about EL34 in triode
or any other recommended tube ?
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Old 29th August 2011, 02:13 PM   #18
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Running 2 x 6C33C and 200V circ rails, I got 56W into 8 ohms, on OTL based loosely on the Allen Kimmel sweep-tube design.....
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Old 29th August 2011, 08:19 PM   #19
tinitus is offline tinitus  Europe
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well, I have considered SE parafeed with 6c33c

but scared me off reading about all sorts of troubles
seems to be experts only tube (?)
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Old 30th August 2011, 04:42 AM   #20
Sk8Ter is offline Sk8Ter  United States
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Default 300wpc Circlotron

I hope you do not mind I have some questions on my HUGE and i mean huge mono blocks..the amp was configured with a 12ax7 voltage gain.. to a 12bl7 driver bootstrapped etc...I thought the amp sounded slow... kinda weird but..anyways I decided to mess around ...did some experimentation on just using the 7199 driving a interstage ..... that did not work. and i dont have a schematic so ...what i am asking ... can someone help me design a good sounding front end to drive the 4.. 2 parallel 6n45c tubes per chanel.....did i mention this thing is a monster!...

Thanks for your help
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