For those who have access to the AES journal, I should mention an excellent article about triode noise calculation AND practical measurements, done by a Neve/AMS designer, one Merlin Blencowe, in the 2013 November issue (Vol 61 Nr 11).
Ha-ha!ruffrecords said:Typical. I was a member of the AES for years but got fed up with articles on surround sound and game sound so last year I did not renew. Then they publish something right up my street.
Cheers
Ian
bockaudio said:Have not read the entire article but found a trouble point. He includes tubes made from the 1950's to 1990's "worldwide production". The 1990's tubes, if from Russia & China, pollute the results fro tubes made by Western countries from the 1950's to about 1970.
Too bad, it was otherwise a rigorous approach.
That's the problem with statistics, selecting the categories. As soon as you make categories, you influence the results.bockaudio said:Have not read the entire article but found a trouble point. He includes tubes made from the 1950's to 1990's "worldwide production". The 1990's tubes, if from Russia & China, pollute the results fro tubes made by Western countries from the 1950's to about 1970.
Too bad, it was otherwise a rigorous approach.
..since grid leakage due to improper vacuum is not a specification...
If the leakage is serious, then yes, it is probably due to poor vaccum. In a 'normal' tube it is dominated by direct leakage between anode and grid, and there isn't a lot you can do about that (except keep the valve socket clean).gyraf said:Do we know that main component in grid leakage is improper vacuum?
Back on topic, my main objection against new-production tubes is that they (in general) seem to vary enormously in average life time, and has huge shifts in operating parameters over time.
Yes. Not enough vacuum either/or pollution. That can be due to leaks, so would be detectable after many years. There may be other reasons that I don't know of. BTW other parameters may vary over time, in particular s parameter decreases with time due to cathode losing its emissive properties.gyraf said:..since grid leakage due to improper vacuum is not a specification...
Do we know that main component in grid leakage is improper vacuum?
Interesting idea! Does anybody currently do this?I can see a potential business in re-vacuuming stock tubes...
Agreed. It seems the current pumping systems are optimized for speed of production. A big contrast to the high-rel tubes of the 50's and 60's, which took as much as 100 hours of pumping in order to evacuate the sublimates.Back on topic, my main objection against new-production tubes is that they (in general) seem to vary enormously in average life time, and has huge shifts in operating parameters over time. Which has more or less forced me to stick with NOS tubes for the commercial Gyraf range - because I'm running minimum-feedback, and am thus dependent on somewhat stable parameters.
Jakob E.
abbey road d enfer said:Interesting idea! Does anybody currently do this?I can see a potential business in re-vacuuming stock tubes...
Yes. Not enough vacuum either/or pollution. That can be due to leaks, so would be detectable after many years. There may be other reasons that I don't know of. BTW other parameters may vary over time, in particular s parameter decreases with time due to cathode losing its emissive properties.abbey road d enfer said:Do we know that main component in grid leakage is improper vacuum?
Interesting idea! Does anybody currently do this?I can see a potential business in re-vacuuming stock tubes...
David, did you have a bad experience with post 1980 tubes?bockaudio said:Serious discussion of vacuum tubes would not include anything made after 1980. We certainly don't use any in our mics, and that's where we make our living.
Incidentally, you can greatly stabilise gm over time by operating at a slightly reduce heater voltage.
This is very interesting and useful. When you say slight reduction what exactly does this mean?
I remember reading somewhere a discussion of reducing 6,3 filament voltages to around 5 Volts for longer life
but I thought this merely decreased gm not also thereby stabilising it.
Bill
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