[Heathkit] Re: Heathkit SB Essay

[Kenneth G. Gordon]

On 13 Jul 2007 at 0:17, Chris Kepus wrote:

> What is a SB-101.5?  Sounds veeerrrry interesting.
> Thanks,
> Chris
> W7JPG

That was what **I** called my much modified and upgraded SB-100 
back in the 1960s.

I bought a mostly finished SB-100 with PS and speaker back then from 
a school-teacher/ham who was moving to a new job.

After finishing it and tweaking it up, I then thought that I would compare 
the circuit with an SB-101 and make the same changes that Heathkit 
did to make my SB-100 into an SB-101.

After that I did some more tweaking and adding a few things, only some 
of which I can remember at this late date in my life.

A couple of things I DO remember:

At that time in my life, I thought that the higher the transconductance of 
the RF, Mixer, and IF tubes, the lower the noise and the higher the 
sensitivity...so I got out all the tube manuals I could find and examined 
them closely for tubes which had the same base diagram as the original 
6AU6s, yet had much higher transconductance.

I can't remember what I finally settled on, but they weren't 6HS6s. The 
ones I used for the RF and Mixer had considerably lower plate 
dissipation ratings than even the 6HS6 and ran really hot, but the 
sensitivity and lack of noise were remarkable.

I didn't have any luck with trying this with the IF because it fouled up the 
gain distribution too much and I was never able to solve that problem.

Since in Missoula, Montana at that time, I had no high-power hams 
near me, the lack of dynamic range was not a problem at all.

I ran a small fan pointed at the rig, and ran it with the lid open.

I also modified the heterodyne oscillator so I could use an external 
crystal.

I discovered that the SB-101.5, when aligned so that the ham bands 
were EXACTLY centered, could be made to cover 500 Khz above and 
below several bands, except 40 meters, for MARS work, simply by 
changing the heterodyne oscillator crystal, and would still maintain the 
same calibration accuracy.

This idea worked quite well on the 20 and 15 meter bandswitch 
positions. 

I then used it on AFMARS, mostly for phone patching, but for other 
uses also.

I did most of my phone patching in the 500 Khz range above 20 meters.

What I had was a sort of KWM-2A.

I also did some other things, which I can't now remember.

I finally carefully wrote up everything I did and sent it to Heathkit.

I was quite surprised to discover that some of my suggestions were 
used in both the later HW-101s and in the SB-102, most notably the 
idea behind their use of the 6HS6, although as I remember it, there 
were one or two more of my tweaks used.

In any case, I thought my SB-101.5 was about the best rig an 
IMPOVERISHED young ham could have at the time.

I also used it heavily for CW traffic handling. I used a foot switch and 
set the VOX sensitivity and delay controls to zero. I would lift my foot 
between every word, and often, between characters. Switching was 
very fast, and I never worried about cutting the first dit. It was a sort-of 
QSK.

I used a McElroy "MacKey" bug, which I still use, and normally ran 
between 30 and 40 wpm.

I thought seriously about some further modifications, like the RIT mod 
that came out in the ham literature about that time, the mod that added 
capacitance to compensate for the Miller effect, which was first 
published in QST in an Hints and Kinks and which Heathkit 
incorporated in later HW-101s and the SB-102, and a full-QSK mod, 
but never felt enough need to incorporate those.

There was also a mod I was interested in, simply because it was 
"interesting", called "Instantaneous Voice Interruption" which someone 
devised for the KWM-2 and published in QST which was an extremely 
fast type of VOX in which the transceiver switched to receive between 
syllables so it acted very much like full-duplex 'phone, but I never did 
this one either. 

Well, that's the story of the SB-101.5.

Ken Gordon W7EKB