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the amp is the Paul Joppa WE model 91 Derivative to replace R10.
thanks
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This circuit is not much mine, I just adapted an existing circuit to use MQ products in a parafeed output. The pentode driver output impedance is very high relative to a more usual triode driver, being dominated by the 91K plate resistor. This makes it very susceptible to leakage capacitance in a grid choke, potentially limiting the high frequencies. Maybe Mike knows how much capacitance there is?
by memory the JR version is approx 15 puffs and the senior version approx 25 puffs
MSL
Builder of MagneQuest & Peerless transformers since 1989
OK, that's much less that the 300B's Miller capacitance so it's not an issue. Full steam ahead!
When your driving the grid of an output tube which is biased tens of volts off of ground you can look at and consider either a M6 (or M4) or low nickel or an admixture (pinstripe) of silicon iron and nickel.
In many respects it is more of an aesthetic decision or choice. Each will sound somewhat different. And IMO it's not that one is better than the other- just as chocolate is not inherently better than vanilla.
Overall M6/M4 has greater drive capacity and if driven well (in the tens of volts) has good permeability.
With lower signal levels the nickels with its characteristic higher perm may be the better choice.
But these are not hard and fast rules and individual sonic preferences come into play here.
MSL
Builder of MagneQuest & Peerless transformers since 1989
thanks for your time to reply Mike... I actually may have a pair of M6 small chokes in the stash... I know I have some hi-nickel, not low but either way a good pair to test.. thanks again - Al
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