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'50+W AB2 Bass Amp Design and Build'
Author:danhei (registered user: 749 posts )
Date: Mon, Feb 20th, 2012 @ 18:07 ( . )

I've long had plans to build a bass amp and am finally going to implement them. Amplifiers I like tend to be multipurpose that sound good with guitar and bass, like Hiwatt and Orange, although I'm not looking to simply clone one as I've been down that road before.

Parts for the cause:

Hammond 373BX PT (700VCT @ 175mA DC, 6.3V @ 5A, 5V @ 3A)
Hammond 1650N OT (60W, 4.3K, UL optional)
2x6L6 or 2xEL34 output (have both types on hand).

B+ should be near 500VDC with SS rectification, and capable of greater than 50 watts output. Leaning towards pentode over UL as 500VDC seems a bit high for UL using EL34s and, especially, 6L6s. 6550s would be better there, but I think B+ current would be too low for them.

Aiming for AB2 operation. Will use cathode or MOSFET followers after PI, DC coupled to output tubes, for greater drive. This leads to my first questions: How do you calculate the negative supply voltage needed for the cathode/mosfet followers (this is a negative supply in addition to the B- for bias). How does one determine the operating point for the CF and calculate how much drive the output tubes require? I've found some example schematics of AB2 amps using cathode followers after PI but it would be nice to be able to go through the PI, CF, and power amp doing the calculations rather than simply copying a design.

Will probably use James-style treble-bass tone stack, though would really like something with a truly useful mid control as well (so no FMV stack!). Any ideas for a good mid control suitable for bass that's not terribly complicated to implement?

Not really tied to particular preamp tube types as of yet. Have standard 12A_7 tubes, along with some ECC88 (designed for cascode operation), 12BH7, pentodes (EF86, 6AU6), and pentode-triodes (6AN8, 6U8).

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--* 50+W AB2 Bass Amp Design and Build
2/22/2012 @ 13:26--Celeste hall
2/22/2012 @ 13:30----Celeste hall
2/22/2012 @ 15:10------Bryan James
2/23/2012 @ 18:23----danhei
2/23/2012 @ 09:23--Bryan James
2/23/2012 @ 18:37----danhei
2/24/2012 @ 10:52------Bryan James
2/29/2012 @ 00:49--------danhei
2/29/2012 @ 09:19----------Bryan James
3/01/2012 @ 00:46------------danhei
3/01/2012 @ 13:37--------------Bryan James
2/23/2012 @ 18:09--tgray
2/23/2012 @ 18:46----danhei
2/24/2012 @ 12:22------tgray
3/02/2012 @ 10:38--------FredB
3/02/2012 @ 11:05----------tgray

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