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In Reply to: RE: Brook 12A bass response? posted by Thermionic27609 on March 12, 2017 at 14:35:46
A 1953 original brook schematic showed the following updates.
R14 R15 changed from 220K to 68K
C12/C13 C14/C15 changed from two .1 to .5
High sensitivity, wide dynamic range, low distortion, and smooth frequency response. Pwk
http://www.itishifi.com
Follow Ups:
Iain42,Where is this updated Brook schematic available? I've found the 1950 SAMS schematic and thought that that was the only one -- with a few errors.
Are you saying that they increased the RC input to the 2A3s to 1uF/68k? Or 0.5uF/68k?
Edit: I found the Brook 22A schematic, which appears to be virtually the same circuit as the 12A implemented with 12AU7s and 6C4s instead of 6SN7s and 6J5s. It doesn't have the same high-pass points as the 12A. The input to the PI is DC coupled from the preceding 12AU7 plate, and the input capacitor has been increased 5x. The driver is coupled to the 2A3s with 0.5uF/100k, plus 1k grid stoppers.
Edits: 03/13/17
I took notes from a Brook 12A 1953 schematic I saw in the Klipsch Museum Of Audio History. It was listed as updates. I am in the middle of a 12a clone build so I am going with the updated version.
C12 C13 to one .5
C14 C15 to one .5R14 68K
R15 68K
High sensitivity, wide dynamic range, low distortion, and smooth frequency response. Pwk
http://www.itishifi.com
Edits: 03/13/17
If you would be willing to post your final schem for the 12A clone (along with pics of course) I would really appreciate it. I have often thought of doing exactly the same thing, and I am casting about for a new project.
Thanks!
I am building from the sams schematic with the changes I saw from the 1953 update. I may make some of the changes mentioned here. I'll try to track changes.
High sensitivity, wide dynamic range, low distortion, and smooth frequency response. Pwk
http://www.itishifi.com
Ah, so the 1953 Brook 12A revised schematic is a physical document that no one has scanned?
True.
It may be released at a later date but out of my control. It turns out these schematics were shipped with the actual Brook amplifiers.
High sensitivity, wide dynamic range, low distortion, and smooth frequency response. Pwk
http://www.itishifi.com
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