Leslie Amps, The 270 ohm fix

[<HOlsen5629@aol.com>]

Leslie Amps, The 270 ohm fix
hammond@zk3.dec.com

> From: Cochran#m#_Stewart@msgate.apple.com (Cochran, Stewart)
> I must have missed this thread. What was it--some kind of Leslie
modification, no doubt?

Stewart:

Bruce (OrganFxr@aol.com) was referring to increasing the value of the 6550
cathode bias resistor in Leslie amps to 270 ohms.  New 122A, 122XB, and 147A
Leslies from Hammond/Suzuki have this update from the factory.  1've never
asked Hammond engineer Warren Brunsting why he made the change but I suspect
it was to lower plate current and prolong the life of the Svetlana 6550s
currently used. 

Svetlanas are the best 6550s presently available but they are NOT Tungsols.
 Tungsol originally developed this tube-type in the mid-fifties and their
versions (three in all) generally were better than the GE, Sylvania, and
other 6550s that followed.  Don Leslie used Tungsol 6550s starting with the
22H and CBS continued the practice after 1965.  Tungsol discontinued their
6550 in the late seventies and early eighties vintage Leslies usually came
with GE 6550s.  The Genalex KT-88 also was an excellent tube but it was too
pricey for OEM use.  The current Shuguang 6550s and KT-88s from mainland
China are cheap but problematic in Leslie amplifiers.  They are short-lived,
inconsistent in quality, and there is a noticeable difference in the sound.
 These tubes are sold relabeled with a variety of esoteric names and Leslie
owners should beware of what they are buying.

Harvey Olsen