[Heathkit] SB-104(A)

[Ulrich Graf]

Hello to the list,

A few weeks ago I was able to get 3 SB-104s from a ham in the
neighbourhood. I want to restore them successively. Two of the three are
real SB-104 As, the third is a SB-104, upgraded to an SB-104 A. While
investigating the boards assembly I noticed that there is one receiver
input board corresponding to the schematic with two diode mixers and the
two circuit bandpass filters, another same board is modified and
supplied with two industrial diode mixers but the third board seems to
be quite different. It has bandpass filters obviously consisting of
three resonant circuits and the mixers are no diode ring versions but
dual gate mosfets. I have never heard about such a version. Is that an
earlier model from SB-104 times and where can I get a schematic from?
Any hints very welcome.

73, Uli, DK4SX