29 Aug
2008
29 Aug
'08
11:13 a.m.
I think, rather, that that's a good portion of the
explanation of why they
were so slow.
Ballpark example, take a 12AU7: the sum of the grid-to-plate and
grid-to-cathode capacitance is around 3 pF. Suppose the network resistance
feeding the grid circuit is 250 KOhm, that's an RC time constant of 0.75uS,
a little better than just 1 MHz. (R can be reduced of course but power
consumption is then on the climb.)
Well, OK, i could buy that, but from what I have seen from the
circuits and construction of tube logic circuits is that the 3 pF is
not much compared to all the stray capacitance kicking around due to
construction techniques.
--
Will