Differences between SB-400 and SB-401?

[Kechkaylo Dave (ATLINKS)]

Dear Harvey:

I have both an SB-400 and an SB-401. The SB-401 was released in 1967; the
SB-400 in May, 1964. The SB-401 was a refinement of the SB-400. There were
some minor circuit design improvements in the SB-401, but most importantly,
the SB-401 has a front panel switch which switches the LMO and BFO between
the SB-300/SB-301 and the SB-401.

To transceive with the SB-400, you had to install an LMO jumper under the
hood and literally disconnect the SB-400's LMO. This allowed the receiver's
LMO to do the main tuning (remove the SB-400 LMO coax between the LMO and
mixer bandpass board. Then add a 7-1/2 inch RG-174 coax between the LMO
input jack on the mixer bandpass board and the phono jack mounted on the
chassis next to the two big 125uF filter caps). If you wanted to transmit
with the SB-400 and receive with the 300 or 301 (like in split operation),
you must remove the LMO jumper coax and re-connect the SB-400's internal LMO
output back onto the mixer bandpass filter board. In addition, you had to
pull the BFO plug on the rear apron of the SB-400; otherwise, the SB-400 and
SB-300/301's BFO oscillators would "beat" with each other when operating in
SSB phone.

The SB-401 fixes this with the addition of a front panel switch. This allows
the BFO & LMO lines to be automatically switched in/out whenever you wanted
to operate in transmit mode or in transceive mode.

Personally with my SB-400 & SB-300 combo, I always operate in transceive
mode, with the SB-300's LMO doing the tuning for both receive and transmit.
Therefore, I never do the cable swapping. Maybe this is what Heath was
thinking about originally when the SB-400 & SB-300 twins were designed. But
this became a pain, so they changed the design.

Also, the alignment steps called out in the SB-401's manual did a better,
more thourough job in explaining the long alignment process.

I hope this helps.

Dave Kechkaylo, W8QIZ

-----Original Message-----
From: Harvey Mitchell [mailto:hmitchell3 at HOUSTON.RR.COM]
Sent: Friday, March 22, 2002 12:36 PM
To: HEATH at LISTSERV.TEMPE.GOV
Subject: Differences between SB-400 and SB-401?


Can someone please advise me the main differences between the SB-400 and
SB-401?  I have an SB-400 that I would like to use with my SB-301, but
unfortunately the manual I have is for the SB-401, and I haven't found any
info on the internet about the SB-400.

Thanks,

Harvey Mitchell, K5YU

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