just a general question on tubes. Is there any rule of thumb regarding plate voltages for any given tube? I mean, if a tube is rated for 450V is it best run at the upper end or kept a bit lower? I know little about tubes and what is the best way to run them. Is there a benefit to running higher or lower voltages?

smegster:

read this in its entirety:

ecp.cc

There will be a quiz tomorrow.

just a general question on tubes. Is there any rule of thumb regarding plate voltages for any given tube? I mean, if a tube is rated for 450V is it best run at the upper end or kept a bit lower? I know little about tubes and what is the best way to run them. Is there a benefit to running higher or lower voltages?

You can run the tube anywhere you want below max dissipation. I tend to like the sound of tubes driven hard if you are looking for a more compressed tone. But, in general, especially in audio amps I prefer a tube driven easy. The tube lasts much longer and seems more at ease.

Yeah, there are basically two schools of thought -- one is Team Over-engineering, in which you run the tubes well within spec, and use more of them if you need more; the other is Team Tubes Are Cheap, in which they run them "hot", because they think they sound better that way.

There is another school of thought. The school of minimum distortion.

Each tube has a particular set of curves and distortion at various voltages

and currents. There is no one rule that fits all. You can usually figure it out

from the plate curve characteristics but not always. Triodes are much

easier to do this with. Typically 60% power is the right number.

Tetrodes and pentodes, and especially beam power tetrodes have to be tested,

but generally the numbers end up 90% of full power.

The output from the transformer on the stacker is 230V, this driving a pair of 6sn7wgta (450v rated I believe) so running at less than optimal perhaps?

Marc, that was a very informative read, didn't understand portions of it as I have no grounding in electronics whatsoever, so still over my head in parts but at least now I know what the parts do and where biasing comes from and what it means now

I would say the tubes are barely coasting from what I can make out. I wouldn't mind driving them a little harder as they are pretty cheap.

You can run the tube anywhere you want below max dissipation.

Most datasheets list a max plate voltage above which arcing may occur.

There is another school of thought. The school of minimum distortion.

Indeed

There will be a quiz tomorrow.

Question #1. What is the major error in that article?

-d

You are running 300V B+ with 10mA of current .

This operating point was chosen after much messing about - we had a variable psu that went up to 450 (iirc) and there was not much subjective increase in SQ above 300. So that is where it was set.

..dB

You are running 300V B+ with 10mA of current .

This operating point was chosen after much messing about - we had a variable psu that went up to 450 (iirc) and there was not much subjective increase in SQ above 300. So that is where it was set.

..dB

"messing about" or "measuring about" I'd rather see measurements that "subjective increase in SQ" ... I guess I don't understand why some of these designs are so void of measurements. Not an attack, really.. I just don't get it I guess.

plenty of measuring about too , the other Mark is a little retentive when it comes to these things. Is this a destiny thing? perhaps you all belong to a secret markl society ( he says as he dives for the bunker (

..dB

heh, *incoming..*

anyways, 300V is good for the round about 60% thinking so I'm happy and learned a thing or two along the way. The questions I ask might sound a bit retarded, but that's only because I am a bit retarded

I can now say I'm not as uninformed as I was yesterday, so that's good.