RIT

[Steve Harrison]

At 05:34 PM 03/30/98 -0800, Sean Pratt wrote:
>Greenies
>
>Has anyone here ever installed RIT into their beloved Heath
>transceivers?  It's something I'm considering doing to my HW-101.  But
>am a little on the terrified side of drilling new holes in it.  Was just
>wondering if anyone thinks it would be a worth while effort?

W6GGV and I did this to his SB101 years and years and years ago. Near as I
can remember, we used an ordinary 1N4007 silicon diode as the varactor. I
*think* we converted the RF gain pot for RIT but I can hardly remember now.
You should be able to do it without drilling holes anywhere. There are gaps
between the sheet metal of the LMO through which you can bring out wires
for the varactor bias, and you can then just "pigtail" things in the air to
terminal lugs mounted under the LMO cover screws and run wires hither and
thither to get the actual bias voltage from some low voltage point. I'm
sure that we used a zener for regulated bias from +12VDC point somewhere.
As I remember it, the 1N4007 worked but didn't provide much frequency
swing. Hank later found a real varactor and installed that for much
improved frequency swing, but I have no details whatsoever now. A look in
some ARRL handbooks and the Solid-State Design manual may give you some
clues of what to try. And yes, you do have to open the LMP; but I never had
any trouble at all with any resulting instability or drift; just be
absolutely certain that you don't move anything inside that you don't have
to, and that you reinstall the cover so it fits tightly.

Another very nice no-holes mod that I did on his 101 and on my SB300 for CW
using the CW filter was to shift the BFO frequency down from its
ridiculously-high 1+ kHz point to something much easier to hear such as
around 600 Hz. As I remember it, this turned out to be really simple; I
believe that I discovered that the crystal provided for RTTY was ideal and
a trimmer capacitor across (or in series with) it provided the final bit of
encouragment to get the BFO where I wanted it.

Unfortunately, however, in the SB101, this had to be switched out on CW
transmit because the new BFO frequency didn't pass through the IF filter on
TX. Also, I only had one of those RTTY crystals which I used for my 300. I
found that I could shift the frequency of the USB crystal just enough to
make a big difference with a trimmer cap and a silver mica, I don't
remember if they were in series with the crystal or parallel. I used a very
small relay to short the caps on TX mode to get the BFO back into the IF
filter passband.

I don't have any other details of any of these mods, sorry; it was too long
ago and the "victims" of the mods are long, long gone as is whatever
paperwork we had.

One easy and simple mod I remember making to my SB300 for greatly increased
sensitivity on the higher bands was to replace the RF amplifier tube with,
I believe, a 6HS6. The two tubes are not exactly the same; one is a
remote-cutoff pentode and the other a sharp-cutoff pentode, I think. And I
believe the cathode and suppressor grids are internally-connected on one
but separate on the other. The effect of plugging in the 6HS6 was the
suppressor grid then ran at the cathode bias because of the internal
connection, I think. This made the AGC behave differently and you might not
like the effect on SSB; I think it tended to pump. But since I only
operated CW and the sensitivity improvement on 10 and 15m was unreal, I
left it in.

Wonder if anyone in the LA area ever found those mods in that old SB300...

73, Steve Ko0U/1

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