Treetop Circuits
Owner’s Manual for SB-51 SSB adapter
Version 4
1
The SB-51 SSB adapter
(Fig. 1)
from Treetop Circuits is designed specifically as an
accessory for the Collins R-388 and 51J series receivers. It provides enhanced performance
in SSB and CW modes. Performance in AM mode is largely unchanged. A 12-volt DC supply
for the receiver’s muting relay is incorporated as an added convenience.
To maintain consistency with the receiver documentation, and in deference to the
distinguished history of these receivers, we use 1950’s terminology -- for example
“megacycles”, not “MHz” -- in this document.
The SB-51 comes as a PC board, ready to install and operate. It plugs into the radio in place
of the detector/AVC tube V110
(Fig. 2)
, and most connections are made through the tube
socket. In addition, two (optionally three) wires are connected from the SB-51 to the radio
and two components are removed. With the SB-51 installed, all controls operate as before,
but performance in SSB and CW modes is markedly improved.
To achieve this improved performance, the SB-51 replaces the diode detector with a high-
level product detector, and provides a fast-attack slow-return AVC circuit. These circuits
are automatically switched in when the receiver’s BFO is turned on. With the BFO turned
off, AM detector and AVC circuits which closely mimic the original circuits are switched in.
Fig. 1 –The SB-51 as supplied.
