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Choke for Class A2 211 Grid?

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Posted on October 9, 2016 at 13:28:49
Triode_Kingdom
Audiophile

Posts: 5732
Location: Texas
Joined: September 24, 2006
Mikey, I'm reworking my 211 SETs to clean up a few loose ends. The existing grid chokes aren't gapped, so I've been looking at alternatives. Based on the schematic below, do you think an EXO-01 parafeed choke would work well at L4? This is a lower-Z circuit than most plate loads, so I think 100H is sufficient. Any comments will be appreciated.

Edit: Just to be sure it's clear, the 6BL7 follower has both sections in parallel. I believe the output Z is less than 100 ohms. Total R in the cathode circuit (including the choke's DCR) is approximately 1,600 ohms.




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Another thought on this..., posted on October 15, 2016 at 14:05:56
Triode_Kingdom
Audiophile

Posts: 5732
Location: Texas
Joined: September 24, 2006
Maybe I should be considering the BCP-15 instead? Its higher current rating might be more appropriate for this use, and 40-50H is sufficient for good response well below 20 Hz.

EXO-001: 100H ------- 20mA ----- 985 Ohms

BCP-15: 50-40H ---- 40-50mA ---- 550 Ohms

Opinions anyone?



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RE: Another thought on this..., posted on October 16, 2016 at 15:43:40
mqracing
Manufacturer

Posts: 4271
Joined: June 29, 2000
Hi TK:

Apologies I'm so late in responding. I would most likely recommend the EXO-001 if the current rating of 20 madc is sufficient.

Though the L is relatively high for the application your looking at... the high AC impedance of the choke has several potential benefits...

the exciting current drawn by the choke is itself a function of the amount of L that the choke has. The more L the less exciting current that is required to drive the choke.

the other consideration... though the BCP-15 has a higher current rating than the EXO-001... it may be in your application illusory...

the max AC current that you can deliver is 1.41 times the standing dc current before the onslaught of current clipping. Running the BCP-15 at considerably less than it's design center can in essence limit (i.e., make lower) it's ability to deliver ac current.

just some thoughts to mull over...

MSL



Builder of MagneQuest & Peerless transformers since 1989

 

RE: Another thought on this..., posted on October 17, 2016 at 13:12:48
Triode_Kingdom
Audiophile

Posts: 5732
Location: Texas
Joined: September 24, 2006
Don't worry about the time Mike, I'm grateful for your advice.

"the max AC current that you can deliver is 1.41 times the standing dc current before the onslaught of current clipping"

Well, that's an entirely new concept for me. Is this independent of core size and design? In other words, if I have a 100 mA choke and a 10 mA choke, and the DC current through each is 10 mA, neither choke can accept more than 14.1 mA of AC without clipping?

Also, let's say I'm driving 140V pk-pk across the choke. That would create approximately 5 ma peak current (10 mA pk-pk) in the EXO-001 at 20 Hz, or 3.5 mA RMS. Which of these versions is the correct one to apply to the 1.41 criteria - peak, pk-pk, or RMS?

Thanks again!



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Buy Chinese. Bury freedom.

 

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