In Reply to: RE: Summertime Blahs posted by Salectric on July 19, 2014 at 12:38:38:
Schematic for the Western Electric 86C should be available online. If you can't find it, let me know and I'll e-mail you a copy. It's basically an input transformer, followed by three identical single-ended voltage gain stages with 262A triodes, then an interstage transformer as phase-splitter/driver, then a pair of 300B in push-pull, then the output transformer. (There's also a super trick distortion cancelling circuit in the output stage, but I'm probably not going to mess with that on mine.)
Designed for amplifying the signal from a sound head, the 86C has way too much gain for home use, so in my amps I have eliminated the input trans and at least one of the voltage gain stages. I'm also not using WECo tubes, since I don't have any 262A's, and my 300B's are slated for other uses.
So my amps will only have one or two of the input gain stages (depending on how much gain I end up needing). I'll be using 56 or 27 type tubes in place of the 262A's. Pretty similar, really. Interstage transformers are UTC LS19's, output tubes are 6A5G's (like a 2A3, but with center-tapped 6.3V heaters). Output transformers are UTC LS57's.
I'm trying to stick with all NOS or vintage parts. Power iron is Chicago transformer Co., chokes are UTC CG series, caps are paper-in-oil. Even the power and signal connectors are NOS old-timey stuff. I'm planning on making a wiring loom and tying the bundles. We'll see how that goes. Chassis are 1/8 inch aluminum, welded at the corners.
Sorry, I don't have a schematic to post. I have 'textbook' values that I'll be starting with, but really, I won't have final values for everything until I start putting it together and check voltages and operating points.
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Follow Ups
- RE: Summertime Blahs - gilmorneau 17:25:55 07/19/14 (10)
- RE: Summertime Blahs - Salectric 10:00:44 07/20/14 (9)
- RE: Summertime Blahs - gilmorneau 13:06:58 07/20/14 (8)
- RE: Summertime Blahs - kstl 22:40:38 04/19/16 (7)
- Using the UTC LS-21 - gilmorneau 15:26:52 05/28/16 (6)
- RE: Using the UTC LS-21 - kstl 23:19:58 05/31/16 (5)
- RE: Using the UTC LS-21 - gilmorneau 07:19:31 06/02/16 (4)
- RE: Using the UTC LS-21 - kstl 11:42:42 06/02/16 (3)
- RE: Using the UTC LS-21 - gilmorneau 17:18:35 06/02/16 (2)
- RE: Using the UTC LS-21 - kstl 21:51:47 06/02/16 (1)
- RE: Using the UTC LS-21 - gilmorneau 22:18:17 06/03/16 (0)