SB 104 vs SB 104A

[Keith Rowland]

Hi Dave:

Personally, I would consider a plain 104 a good source of parts, many of
which are no longer available, for my working 104-A rigs.

Heath was working on the very outer edge of the technology of the day
when they brought out the SB-104, their first solid-state rig.  It was a
catastrophe. Birdies in the receiver, garbage on the transmitted signal,
poor CW waveform, finals that self-destructed at the slightest hint of
SWR, the display fluttered, the TR switching had transients, etc., etc.
They spent about four years re-thinking the rig, and then came out with
a mod that was almost a rebuild of the rig.  The mod transformed it into
an SB-104A, which still has some very audible birdies, especially on 10
meters.

I have two SB-104As, and a good thing.  You need the spare rig to use
while you're working on the other one.  Even at that, in the 5 years
I've had them, the entire final board on one has been rebuilt (including
the finals, which still tend to blow up if you drive the rig past "6" on
the meter scale while transmitting), a mod had to be devised to the
power supply, which would blow the 20-amp fuse at times when
transmitting, due to transmitted RF, the plug-in circuit boards have to
have their pins cleaned and excercised about every 6 months to keep the
connections solid,  plus numerous ongoing other repairs.  Also, recently
the VOX circuit has gone west.  When you speak, it goes into
oscillation, creating a varying carrier that sound absolutely awful on
the air.  Have replaced several likely components, but no luck so far.

The other rig blew both the 5 and 11-volt regulator chips (available now
only from one source that I know of, and at something like $20 apiece),
necessitating a redesign to use readily available 3-legged regulators,
and at present it has failed on all the 10-meter band positions--it
transmits fine on all bands, but on all 10-meter positions, enormous
birdies sweep across the entire band, and no signals are received.
Alignment has not solved this problem.

Despite all this (and I haven't listed all the problems), I like the
SB-104A.  I use them every day, have worked over 200 countries, mostly
on 20 meters, and during the sunspot minimum at that,have never failed
to work any station that can be heard, they have marvelous audio, the
controls are well-placed and large enough to see, the digital readout is
big and clear, and the entire SB-line (which I have, including the
SB-230 amp), still looks really good all lined up on the operating
table.  You can see the lineup on my webpage at:

rowland1.home.mindspring.com/hello/index.htm

I have to say, though, that anyone who is not an engineer may well find
these rigs beyond their capability to keep them going.  Even with a
BSEE, nearly 50 years as a radio and TV consulting engineer, and 45
years as a ham, I'm still having trouble second-guessing the original
design engineers, as evidenced by the fact I haven't yet been able to
solve the above-mentioned problems with the two that I have!

I'm posting this reply to the list because, judging from postings during
the past year or so, I notice that these rigs are still popular, and
maybe this info will be of use to others besides yourself, who are
interested in the SB-104(A)s.

73,

Keith

David Humbertson wrote:

> Hi guys,
> Can someone tell me the difference(s) between the
> straight 104 and the A version. They were popular
> at a time when I was not following Heath gear too
> closely. Is a plain 104 to be avoided if possible?
>
> Thanks
>
> 73,  Dave - W3NP
> Ft. Ashby, WV
>
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