G - RX Front End
Updated Schematic
[
UHD Schematic
]
SB-104 => 85-1666-1
Heathkit Changes
(March 24, 1976)
from SB-104-31
Improved Sensitivity
(Does not apply to 85-1931-x)
The following change should be made to all HW/SB-104's received for service:
Remove and discard L733
Remove and discard C787
This change eliminates the series resonant circuit from the colector of Q703 to ground, and improves the performance of the PN 40-1875 coil at L734.
[
85-1708-1 without above mod
]
[
85-1788-1 without above mod
]
All older front end boards shown below have the inproved sensitivity mod applied.
Updates (SBM-104-1)
PC Board
X-Ray
Schematic
SB-104 => 85-1708-1
PC Board
Board XRay and schematic same as HW-104 85-1788-x below.
HW-104 => 85-1788-x
PC Board
Alignment
X-Ray
Schematic
As modified re. SBM-104-1
8.65 MHz Reject Filter
The SB-104A does not have this reject filter.
Reject filter photo from SB-104 manual
This reject filter is wired differently than the following directions.
SB-104A => 85-1931-1
PC Board
Homemade board? Photo resist but no solder mask?
Alignment
X-Ray
Schematic
Modified for use in HW-104
©2008
WB4KDI Dave J. Barnes
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