104/104A

[John Farrington]

At 09:24 AM 09/03/2001, W0AKG wrote on the Heath reflector:

>Can any body tell me the main difference between the SB 104 and the 104A ?
>Thanks guy's.
>Martin L Tippin  W0AKG
>140  Monarch Lane
>Branson,  MO  65616


Quite a lot - besides the later 104-A's that came from the factory, there were
2 field modification kits so owners could update both their original SB-104
and its power supply, the HP-1144.

The 104 upgrade kit was quite extensive, with a 40-page manual (# 595-2016-03),
and took me a few days to put in. The main item was a completely new factory-
assembled front-end board which replaced the poor-performing original, but
there
were also numerous wiring and small part changes throughout the radio. Included
were new SB-104A assembly and operation manuals. Sorry, the following outline
doesn't contain much detail, as that would be too long for for me to type.

Changes made:

- new front-end board (factory-assembled)
- VFO mods
- VFO/filter board (new board)
- xmtr audio/reg board mods
- HFO/premixer board mods
- carrier generator/xtal filter board mods
- rcvr IF/audio board mods
- power amplifier board mods
- driver board mods
- ALC/output board mods
- underchassis wiring & pushbuttons, and small parts
- CW xtal wide and narrow wiring mods
- RF detector circuit mods for the panel meter
- different alignment instructions in the new manuals.
- a new trim strip was supplied for the front labelled "SB-104A".

As I recall, one of the pushbuttons on the original SB-104 turned on/off the
last digit (tenths) of the frequency display, because Heath thought the
frequent flickering might bother some operators;  the upgrade kit eliminated
that function, so the last digit stays on all the time.

Although performance was better, in the following years there were several
articles in various ham magazines describing further improvements that owners
could make.

The modification kit for the HP-1144 power supply had a 16-page manual
(595-2219) plus an illustration booklet;  the modifications included a whole
new regulator board with a crowbar overvoltage protect circuit. There was
quite a bit of new chassis wiring, plus new power transistors.

73

John   KE5ZB

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