Phase inverters symmetrically "split" the incoming (unbalanced) preamp-signal
into two "balanced" signals out of phase by 180 degrees to drive
the push-pull output tubes to maximum efficiency. Various phase inverter
designs include: the "long-tailed"
paraphase," and "split-load"
In all Vintage H.H. Scott products these tubes are configured, as one of
two inverter types:
During manufacturing production runs (of particular Scott types -- the
factory often substituted the presently more expensive and harder-to-find, 7199 for the older (and more common)
6U8 -- 6GH8 -- 6BL8. The two tube types are not pin-out interchangeable, as their
triode sections are pinned differently.
HOW TO: Convert from 7199 to 6U8 Phase Splitters
However, with a simple re-wiring of the
7199 tube sockets the stock circuits are identical. WARNING: DO NOT SUBSTITUTE a
6U8-family tube for a 7199 without first performing this MODIFICATION!
Use the table below
as a guide:
-- 6GH8 -- 6BL8
Typical Scott Amplifier (with "Split-Load" Phase Inverter -- 6U8) Schematic --