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Re: Gizmological Heresy?

Posted by Ralph (M) on December 18, 2000 at 13:55:05

In Reply to: Gizmological Heresy? posted by Wayne on December 15, 2000 at 18:25:35:

Despite the fact that two tube sections may show quite a disparity in a tube tester, the fact of the matter is that the tube has a mu of 2. 2 is not very high (in fact it is quite low :)). The result of this is that the relatively major changes in tube operation demanded by the simple setting of the bias point and the very large input signal from the driver are actually fairly close in tubes that check relatively far apart from each other. Yes, they won't be a match but their operation will be quite close to each other and won't be off by a factor of three as in the above example.

If the mu was even a little higher we would never be able to get away with this. The problem is: 16 bias contols in an M-60? 28 in an MA-1 etc. It's not needed. Even if the tubes *were* all set this way, their AC characteristic would be unchanged.

If we were to have seperate bias settings, it would require a coupling cap for each control and a driver tube section to go along as well. A nice exercise, but research indicates that the amp would never be set up right and would never sell. So we have the very practical matter of the amp being suddenly very impractical.

Harvey is essentially trying to call me on the carpet over this issue which is one any OTL manufacturer has to face: triodes or pentodes (and how many of each)?. What we found is that the mu is more important then the number of tubes- you'll have *way* more trouble with 4 triodes with a mu of 4 then you will with 16 with a mu of 2!!

The ultimate solution is a custom triode- good luck with that in this world of fading tube technology. So our choice seems to be the correct one.

The *REAL* problem here is that Harvey doesn't listen- I tried to explain this to him 4 years ago.

Need I point out that he has not heard an M-60 in the intervening four years? He hasn't heard what the resistors in the output section do, any of the driver changes, never heard the Caddock resistor package, optional caps, etc. etc. In basic terms, he's a loose cannon.

-Ralph

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