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Old 9th July 2006, 07:06 PM   #11
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They are half the power of 6C33c so the output might be half of it.Perfekt!
Not quite, the current of a 6C41 is half of a 6C33C so power will be 1/4, (P=R*I^2) that is one of the basic problems with building a small OTL, power falls quickly with current and effciency will also be lower, it is easier to make a high power OTL, my OTL with 4 6C33C give about 4 times more power than the one with 2 tubes.

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Old 9th July 2006, 09:06 PM   #12
Ryssen is offline Ryssen  Sweden
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Well if I use 4 6C41/chanel will that be the same as 2 6c33?Might as well use 2 6c33c then. What about SE OTL with one 6c33c,will that be 1/4 of the power,I mean I have built in DC protection,the output cap.
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Old 10th July 2006, 04:16 AM   #13
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ARG Audio Labs built a 5 watt SE OTL with only one driver tube
and a single 6c33c per side. I believe they went out of business.
I fore one would like to see their circuite.
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Old 10th July 2006, 05:20 AM   #14
Jeb-D. is offline Jeb-D.  United States
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There is no way 1 6c33c can run as a 5w OTL. If they were claiming that, there full of it. Unless they had some kind of high Z speakers to go with it. 1 6c33c would give you 1Wpk @ 16ohm load or .5Wpk @ 8 ohm load. Any higher would require exceeding the tubes Imax parameter.
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Old 10th July 2006, 05:39 AM   #15
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A 6C33C have a maximum allowed contionous cathode current of 600mA and that will give an output power of 1.44W in 8 ohm, I would not recommend to go much above 600mA so thats it.

In a class AB amplifier it is safe to run much higher peak currents, although max allowed peak current is not specified for the 6C33C experience show that there is no problem to run peak currents of 2.5A or more if the average current doesn't go much over 600mA. Also in a class AB amplifier while playing music the average current will be much lower than for peak conditions which give very long life of the ouput tubes.

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Well if I use 4 6C41/chanel will that be the same as 2 6c33?Might as well use 2 6c33c then.
I would recommend to use 6C33C in that case as it there will be no problems with tube matching, using parallell connected output tubes always give a whole range of new problems that it is better to avoid if possible, that is one reason why 6C33C is so an ideal tube for an OTL as it gives substantial power and low output impedance even for one pair.

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Old 10th July 2006, 05:55 AM   #16
Jeb-D. is offline Jeb-D.  United States
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Tubetvr, thanks for pointing out that the Imax of the tube is for continuous not peak. That gives me more room to play with in one of my designs.
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Old 10th July 2006, 06:14 AM   #17
Ryssen is offline Ryssen  Sweden
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Just to be sure,2 6C41/chanel gives about 6-7w/channel/8 ohm?
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Old 10th July 2006, 06:41 AM   #18
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Just to be sure,2 6C41/chanel gives about 6-7w/channel/8 ohm?
Assume that we build a class B amplifier then the peak current is Pi * average current over one period. For 6C41C allowed max average current is 350mA so peak current can be ~1.1A which gives ~4.8W in 8 ohm, (Pout = Ipk^2*Rl/2). This calculation is valid also for a class AB amplifier but efficiency is lower due to higher idle current.

Given that it is an amplifier for music you can allow for a higher average current than specified as the current peks only will happen during music peaks which normally are 10 - 20 dB higher than the average output power when the ampliofier is close to clipping, so 6-7W seems reasonable and will give long life, an idle current of ~100mA should be OK.

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Old 10th July 2006, 11:32 PM   #19
Ryssen is offline Ryssen  Sweden
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Well id I decide to build one in any form is it wise to use a DC protection?Any one had a failure,blown a speaker?
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Old 11th July 2006, 05:22 AM   #20
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is it wise to use a DC protection?Any one had a failure,blown a speaker?
IMHO it is not needed, a fuse in the B+ line is enough in the unlikely event that a tube develop a catasthrophic failure. The speaker can withstand a DC voltage during the time it takes to blow the fuse, if one is anxious why not use ultrafast fuses.

If the fuse method is not deemed acceptable it is easy to build something around a window comparator that after LP filtering checks the DC voltage and switch of B+ in the event of failure.

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