Anyone know of some ridiculously powerful triodes for class A useage? - diyAudio
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Old 16th March 2009, 04:53 PM   #1
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Default Anyone know of some ridiculously powerful triodes for class A useage?

For about 100-500wat output, maybe with different frequency responses (I'm designing a BIG 2-4k tri-amped system) perferbably with 0.1% distortion (you can always try lol). I was looking in to ones used for transmitting but most of the one's I've seen have about 5% distortion, Svetlana have some explicitly described as possible class A useage.
I was thinking get some ones that would be overpowered and reduce the operation conditions to reduce distortion? Cheers for any help on this I proper want to do it!
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Old 16th March 2009, 05:10 PM   #2
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look for a 6C33 (Rusian tube).
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Old 16th March 2009, 05:24 PM   #3
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You want ridiculous power, you need a big transmitting tube. My favorite, the 833A. You will need a big power supply, a good OPT and some serious cooling since the filament alone eats 100 watts. I could get an easy 200 watts in A2, 50 watts in A1 came at 0.9% distortion. To get to 0.1% you will need NFB and a really really good OPT.

http://www.tubelab.com/833SE.htm
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Old 16th March 2009, 06:03 PM   #4
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hey-Hey!!!,
The Eimac 304TL has gain of a 211 with less plate resistance than a 2A3. It also has a 300W anode dissipation rating( just like the 833 ). Filament is 25A/5V. There is also bigger, 450TL and 750TL if yer truly nuts... or the Russian GM100
cheers,
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Old 16th March 2009, 06:21 PM   #5
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Quote:
Originally posted by tubelab.com
You want ridiculous power, you need a big transmitting tube. My favorite, the 833A. You will need a big power supply, a good OPT and some serious cooling since the filament alone eats 100 watts. I could get an easy 200 watts in A2, 50 watts in A1 came at 0.9% distortion. To get to 0.1% you will need NFB and a really really good OPT.

http://www.tubelab.com/833SE.htm
Yeman I've already found your page, it's well informative! The lnik's not working right now though
And Bandersnatch the GM100 looks the most plausible right now since it's got the highest output but there might be more. I'm probably going to ring all the valve manufacturers in the UK (because that's where I'm from and it'll be easier to co-ordinate supplies) and ask their opinions.
I was also going to make it OTL for full range response (Atmosphere so they can get 2Hz out of their OTL stuff)
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Old 16th March 2009, 07:26 PM   #6
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If you can't find triodes big enough, Fake it!

Though for reasons of grid leak at very low plate voltage,
I had to abuse the triode's plate more like a screen in UL...

Whatever, its OTL except for the cap... I'm working on it.

This is largely based upon Nelson Pass' Zen + Aleph.
Bent around a Triode's 4th circuit. Plate in > Cathode out...
35W ain't too bad for one half of a 12AU7 in SE.

-----------------------------

Look to Tubelab's Super 45 for further inspiration:
http://www.tubelab.com/SuperTubeSE.htm
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Old 16th March 2009, 07:54 PM   #7
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Quote:
I was also going to make it OTL for full range response (Atmosphere so they can get 2Hz out of their OTL stuff)
That changes everything. If you are using conventional speakers with the typical 8 ohm impedance you need to source (and sink) a lot of current. Several AMPS are required for the 100 watt range. This isn't going to happen with any reasonable transmitting tube, and is going to require several low impedance tubes in parallel, or some solid state assistance.

Yes Atmasphere gets a low cutoff frequency without output transformers but it takes a big bunch of 6AS7's in parallel to do it. The 6AS7 is the lowest cost tube capable of handling some current. The next step up is the 6336A or the 6528, these get expensive. Beyond that there is the 7241 or 7242, big bucks though.

If you are using electrostatic speakers it is possible to drive them directly with sweep tubes, but then you don't need a 2Hz corner frequency unless you have really big speakers.
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Old 16th March 2009, 08:03 PM   #8
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Just a few thoughts - it seems that ur rather completely unclear as to what it is that you actually want to do.

All of these big high power transmitting tubes require very very high voltage and almost all of them also have a comensurately high plate impredance that means a difficult to build output transformer.

Then too these tubes are not designed as Class A tubes, so you have to run them at a substantially lowered plate voltage and adjust the bias - while that may get you into the range of class A It surely will not give you anything near 500watts of class A, even in PP. You actually have to derate the tube substantially compared to its Class B spec.

Then you also have to drive them with something substantial in most cases... depends a bit on the tube's gain, but it's not going to be a 12AX7 usually.

Suggest that you think through your project more fully and narrow down the real world specs that you need to acheive before deciding that you want or need?
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Old 16th March 2009, 11:58 PM   #9
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I'm collecting the bits Lumps of brass for the heater connectors, teflon base, Ally stock to turn for the top caps. 813 for the antitriode, 350W rewound toroid. Modded PC supplies 10V 20A.1200V 1A supply.
Will start at the end of summer.
Mike
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Old 17th March 2009, 01:27 AM   #10
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You could always run an Eimac 8974 in triode...
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