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Voltage Q: 6L6GT SE cathode bias

10/18/2003 2:04 PM
Peter Rasmussen
Voltage Q: 6L6GT SE cathode bias
What's the highest recommendable plate voltage for a 6L6GT in single ended cathode biased operation?  
10/21/2003 10:39 PM
Le Basseur
The average value for the fk voltage potential is 180V,assuming that the filament is somehow grounded.Personally,I went a few times to 100-120V,assuring a proper (higher than 0V)potential for the filament,just to avoid any risk of breaking the filament's insulation.  
However,most of the time I saw around 80-90V on schematics,wich is perfectly common-sense.  
What is your application,if you need some higher vk?
10/22/2003 1:25 AM
Rob Mercure

Hey Peter,  
Out of curiosity - are your specifically asking about the original glass 6L6 - as opposed to any of the upgraded "B" and "C" versions? Anyhoo, SE and cathode bias really don't affect the maximum Ep which is 360V for the 6L6GT.  
10/22/2003 6:48 AM
Peter Rasmussen

OK, from the start, the idea is build a champ-like class A amp with a 6L6GC. Designing the powersupply (and figuring out what tranny to go with) I'd like to know how high a voltage I can put on the plate and still operate within class A and not destroying the tube...  
Next, I'm a amp-build novice (if you haven't already guessed it!), and any hints/links/help to where I can find some more comprehensive, but still understandable, litterature on ampbuilding/tubeoperation would be greatly appreciated!
12/1/2003 10:12 PM

I believe, by definition, all SE amps are class A; there's only one tube so it must bo "on" all the time.
12/2/2003 1:33 AM
Rob Mercure

Not so - and as fate would have it - I commented on this in one of the other forums. Class A just means that current flows through 360 degrees and, if one wants minimum distortion, a single tube must be Class A. But it ain't perxactly the same thing. Lots of radio frequency oscillators and amplifiers operate SE in Class C where current flows less than 180 degrees using a resonant "tank" circuit to create a sine-type waveform. And we musn't forget tubes used for DC purposes or switching. And, for yucks, you can bias a Champ type circuit to scant AB1 and get some interesting, and nasty distortion artifacts.  

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