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In Reply to: Re: My first OTL Circlotron posted by Lew on January 20, 2006 at 14:34:39:
Do You Speak about this link? http://members.aol.com/aria3/otlpaper/otlhist.htm This's the only article I've fond. Could you tell me about the sound of this amp. Could you explain how to calculate the power supply for it & output power. I can't understand How can it give so great power it the peak current 6c33c tube the only 600mA?
Follow Ups:
The URL you posted above takes you to Kevin Covi's article on circlotrons that I think was part of the old ASOG archives. From the bottom of the pages you can go to one of his schematics. The schematic posted below by tubetvr is for an OTL, but that is not a circlotron output stage. It appears to me to be a "totem pole" type of output stage that is characteristic of the Futterman-type circuit. I mean to cast no aspersions on the Futterman type OTLs; I used such amplifiers myself for ca 20 years without problems. I am just pointing out that if Neon wants a circlotron schematic, the one posted by tubetvr does not qualify as such. By the way, Neon, it used to be true that the M60 Owner's Manual had an M60 schematic within. Atma-sphere used to sell the Manual to interested persons for a nominal fee. If this is still the case, you might try that source for a schematic as well.
how much does this schematics cost? Do you know?
Since I already wrote that I am not sure that the manual is still available to non-owners of the M60 (and other) Atma-sphere amps, I can hardly be relied upon to tell you the price. You should contact Ralph Karsten or Bill Layer at Atma-sphere. It's probably 50 bucks or less, maybe much less.
"I can't understand How can it give so great power it the peak current 6c33c tube the only 600mA?"6C33C is specified to 600mA max average cathode current
but there is no problem to let the peak current go up to a much higher value. I am using 6C33C at peak currents uo to 2.5A without any problems but note that the average current is then only ~0.8A so not so much above the specified maximum. 2.5A peak current give 25W output power in 8ohm, 6C33C can give higher than 2.5A, 3A or more is not a problem but I decided to play itself and limit the current to 2.5A.Rgds Hans
If it isn't to much for you could you tell me how to calculate the output power and a peak current for 6c33c?
Output power is P=R*I^2 where I is the RMS current in the load. If we assume that only one tube is sourcing the current at peaks which is the case for class AB then the peak current must be I*SQR2. Note also that each tube will only source current for half of the period as it will be more or less cutoff for the other half. Given this assumptions we can calculate the necessary peak current for a given power which will be Ipk = SQR(2P/R) and the average current through each tube which will be IRMS/(2*1.1) (2 due to what I wrote above that each tube don't conduct current during more than half of the period and 1.1 which is the difference between the RMS and average of a sinewave current).An example: 25W at 8 ohm give peak current of SQR(2*25/8) = 2.5A and the average current is SQR(25/8)/(2*1.1) = 0.8A
Normally tubes are not specified for peak current but only for the maximum average current so it is not given that any tube can be used in this manner. Max peak current depends on cathode emission and differs between different tubes, some are very marginally designed when it comes to cathode emission and some other have very overdimensioned cathodes, 6C33C seem to be one of these.
Regards Hans
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