Parts List for REV2, REV3, REV3A, and REV4 SC-50 Squelch and CTCSS boards:
All board versions are functionally equivalent.

REV4 boards (shipped after Jan 1, 2016) include 5 changes:

1. An added two-pin header which can jump pin 2 and 3 together on the DB25.  
The header physically goes between the squelch pot and C21.  It's called SJ5.
Installation of a jumper (short) on this header allows discriminator audio 
to be put to the input of the high-pass filter without doing it at the DB25 
connector.  A jumper is also provided for this header.

2. A few more resistors are now mounted normally (flat - against the PC board)  
instead of vertically - namely R5, R24, and R27.

3. Added a convenient 9.6 Volt test point.

4. The voltage regulators inputs are now wired in parallel.  On board revisions 
REV3A and prior, the 5V regulator was sourced from the output of the 9.6V regulator 
and somewhat limited the maximum source current for the logic high open collector 
(PNP) outputs. 

5. All .1uF film capacitors are now .12uF film of the same manufacturer. There is no 
functional change due to this part value change.  

U1 - 78L09
U2 - SC6709 or M7716 (Motorola - optionally supplied)
U3 - 78L05
U4 - FX465D5 (CML)
16 pin dip socket for U2

Q1 - 2N2222 
Q2 - 2N2222
Q3 - 2N2222
Q4 - 2N2907
Q5 - 2N2907
Q6 - 2N2222


(4 - 2N2222, 2 - 2N2907)

D1 - 1N4004
D2 - 1N4148
D3 - 1N4148

(2 - 1N4148)

D4 - LED - Green
D5 - LED - Blue
D6 - LED - Red

R1 - 15 ohm
R2 - 27k
R3 - 180k - mounts vertically
R4 - 4.7k
R5 - 10k - mounts vertically on all but REV4 boards
R6 - 1k  - mounts vertically
R7 - 220 ohm
R8 - 100 ohm
R9 - 4.7k
R10 - 10k
R11 - 4.7k
R12 - 1k
R13 - 680 ohm
R14 - 100 ohm
R15 - 10k
R16 - 10k
R17 - 560k
R18 - 820k
R19 - 22k
R20 - 10k Pot
R21 - 1 Meg
R22 - 4.7k
R23 - 4.7k
R24 - 1k  - mounts vertically
R25 - 1k  - mounts vertically on all but REV4 boards
R26 - 1k  - mounts vertically
R27 - 10k - mounts vertically on all but REV4 boards

RD - 22k - User supplied - mounts vertically
RX - User determined - User supplied - mounts vertically


(5-10k,  5-1k,  5-4.7k, 2-100 ohm)


X1 - 4.000 MHz Crystal

S1 - 6 position DIP switch

SJ1-2 - 3 position header (green)  with short (might be blue)
SJ3-4 - 3 position header (yellow) with short
SJ5 - 2 position header (white) with short - REV3A and later only.

C1 - .47 uF
C2 - .12 uF
C3 - 4.7 uF
C4 - .12 uF
C5 - 22 uF
C6 - 4.7 uF
C7 - .001 uF
C8 - 100 pF SM
C9 - 470 pF SM
C10 - .01 uF
C11 - .22 uF
C12 - 3.3 uF
C13 - 2.2 uF
C14 - .47 uF
C15 - 4.7 uF
C16 - .12 uF
C17 - .47 uF
C18 - 18 pF SM
C19 - 33 pF SM
C20 - .12 uF
C21 - .12 uF
C22 - .12 uF
C23 - .47 uF
C24 - .12 uF
C25 - .12 uF
C26 - .12 uF
C27 - .22 uF
C28 - .15 uF
C29 - 750 pF SM 300V
C30 - 100 pF SM
C31 - 47 pF ceramic
C32 - 47 pF ceramic
C33 - 47 pF ceramic
C34 - 47 pF ceramic
C35 - 47 pF ceramic


(4-.47uF,  9-.1uF,  3-4.7uF, 2-100pF SM,  2-.22uF,  5-47pF)

DB25 Female chassis connector

Masters Communications SC-50 Squelch-CTCSS circuit board  (current revision)