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help with Grid Choke selection

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Posted on September 7, 2016 at 04:19:09
awsjr
Audiophile

Posts: 144
Location: Austin, Tejas
Joined: November 30, 2006
the amp is the Paul Joppa WE model 91 Derivative to replace R10.




thanks


 

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RE: help with Grid Choke selection, posted on September 10, 2016 at 20:23:51
mqracing
Manufacturer

Posts: 4307
Joined: June 29, 2000
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

 

RE: help with Grid Choke selection, posted on September 12, 2016 at 02:42:59
awsjr
Audiophile

Posts: 144
Location: Austin, Tejas
Joined: November 30, 2006
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

 

RE: help with Grid Choke selection, posted on September 18, 2016 at 01:15:16
Paul Joppa
Industry Professional

Posts: 6694
Location: Seattle, WA
Joined: April 23, 2001
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?

 

RE: help with Grid Choke selection, posted on September 18, 2016 at 16:32:21
mqracing
Manufacturer

Posts: 4307
Joined: June 29, 2000
by memory the JR version is approx 15 puffs and the senior version approx 25 puffs

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: help with Grid Choke selection, posted on September 19, 2016 at 04:43:56
Paul Joppa
Industry Professional

Posts: 6694
Location: Seattle, WA
Joined: April 23, 2001
OK, that's much less that the 300B's Miller capacitance so it's not an issue. Full steam ahead!

 

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