SB 104 vs SB 104A

[The Maryland Crofts]

Hi Keith, Dave and everyone-

That's interesting . . . while I do not presently own either the SB- or
HW-104 (its been at least 15 years) I have had some operating experience
with the SB . . . the only difficulty I ran into here is low rf output .
. . traced to poorly wound baluns (coils not "tight") on the high power
transistor output board . . .

as for the HW-104 (which I thought the only difference was an analog
dial versus the "digital" dial) the one I owned required some modest
repair but I had faith enough in it to run mobile for over a year (and I
left it installed in the car year-round so it "suffered" from temp
extremes too) . . . I noticed the birdies on cold days . . . but after a
warm up (and periodic connector pin exercising as Keith describes) I was
off and operating!  Back then the 25 kHz cal sig was handy to keep me
above the 28.5 band edge when on 10.

Keith Rowland wrote:
>
> 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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