Aligning the SB-303 and SB-401any trick to make OSC's more robust and sure starting????

[Michael Waldrop]

According to the SB-303 manual, page 129, there are a few mods required to
the SB-400 and SB-401 to allow it to work with the SB-303 in transceive
mode. The mods are listed below:

SB-401 mods to transceive with the SB-303 (per SB-303 manual page 129 and 130)

1. Locate the 100 ohm (brown-black-brown) 1/2 watt resistor on the front
panel Frequency Control switch. Replace it with a 68 ohm (blue-gray-black)
1/2 watt resistor.

2. Locate the mixer-bandpass circuit (small board behind the LMO) and remove
the 6EW6 tube (V4) along with the tube shield

3. Remove the 21 Mhz trap coil (part # 40-479)

4. Remove and discard the 270 ohm (red-violet-brown) resistor and the 100pf
capacitor combination. In its place install a 270 ohm (red-violet-brown) 1/2
watt resistor.

5. Replace the 6EW6 tube (V4) and shield

6. Replace the cabinetand reconnect cables.

That's all the manual says for the SB-401.



SB-400 mod to transceive with the SB-303 per the SB-303 manual page 129.

1. Locate the RCVR LMO phono socket on the rear apron. Connect a 68 ohm
(blue-gray-black) 1/2 watt resistor from the center lug of the rear apron
RCVR LMO jack to the center lug of the RCA jack ontop of the chassis behind
the rear high voltage capacitor. This is all accomplished from under the
chassis.

On the SB-400 you will have to remove the short cable from the SB-400 LMO
output that connects to the mixer board, remove it and set it aside. Connect
a short length of RG-174 coax with RCA male connectors on both ends between
the LMO output and the RCA socket on the top rear of the chassis, directly
behind the rear most high voltage capacitor. Then connect the cables between
the SB-400 and the SB-303.

That's it for the SB-400.

Whether this will work or not, I can't say. I have not tried it since I use
seperates all the time either with my SB-300 or SB-303. I also recommend
reviewing all SB-303 and/or SB-400/401 technical bulletins for any
additional information.

73's

Mike
W5RKL

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