Bob says:
>IMD increases because there is no such thing as 2 perfectly matched tubes.
>Uneven load sharing no matter how small will increase IMD.
If you stick in any 4 tubes selected at random from tubes with the spread of
sweep tubes or even 6146Bs, you will have trouble, but with reasonable
design and matching, I can't say that I agree. Collins and Redifon were
amongst those companies that produced PA's with 3 and 4 tubes in while
meeting exacting professional IMD specs. Unless the mismatch is large, the
IMD will not suffer in a measurable amount.
Matching by adjusting the individual screen voltages is a well known
technique. BTW, what about distributed amplifiers - they use paralleled
tubes in great numbers and achieve good linearity.
73
Peter G3RZP
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