[Boatanchors] Early vs Later Mohicans

[Philip Atchley]

Hi,

I posted the following to the Heathkit reflector, but thought some folks here 
might be interested too.  It is after all a "baby boatanchor" or perhaps a 
"Dingyanchor" dating to the early 60's.

"Somewhere" I had read that the difference between the GC-1 and GC-1A Mohicans
was only in the knobs, dull metal vs. chrome.  Mine is a GC-1 with the duller
knobs (That W6LRG polished for me).  HOWEVER, there are apparently other
differences as well.  Mine has a Hi/Lo antenna Impedance slide switch on the
back that ISN"T shown in the GC-1A schematic on BAMA.  There is apparently
other circuit differences too, at least in some of the very early ones (see
below).

Yesterday I posted a question concerning a "missing" 6 Volt Zener diode in my
Mohican and how the radio had severe frequency pulling with strong signals.
Especially on the higher bands.

I surmised that perhaps the builder had either forgotten to install it or
didn't know what to do with the "extra" diode.

Well, after doing some "reverse engineering on this set I've determined
conclusively (at least to my satisfaction) that this must have been an "early"
model and never did have a Zener diode.  This based on the following.

1.  Resistor R51 is 100 Ohms instead of the 270 specified in the schematic.
2.  The wiring to the BFO switch in this set wouldn't allow the 6 Volt Zener
Voltage to appear across the BFO AND 9 Volts on the AVC switch.  The Zener mod
apparently required a slight wiring change.

Today I decided to add the Zener to my set.  I replaced R51 with a 270 Ohm
resistor and then added a 6 Volt Zener from the low side to ground.  (Actually
back to back 5.6 V Zener and a silicon diode, gave me 6.1 V) The set worked,
but had low gain, with the S meter reading mid scale with no signal.
REBIASING the AGC line by reducing the value of R1 to 33K returned the gain
and S meter returned to Zero. The set then seemed to perform better on all
bands. (NOTE, the BFO STILL has 9 Volts with this mod I chose not to rewire
the whole chassis).

At that point I went through a thorough alignment and was pleased to discover
that the set was MUCH easier to align, especially on the higher bands where
frequency pulling had formally made alignment difficult and "iffy".

How does it play?  MUCH better, I really can't over emphasize that too much.
Now if I tune in a strong station at 17.8 MHz, it doesn't drift back and forth
in frequency as the station fades.  Even more noticeable is the fact that I
can copy the local trash on the 11 Meter band and tuning stays "put" on a
channel as stations of different strength come and go (as much as any 11 meter
signal can be expected to "stay put").

73 de Phil,  KO6BB
991 Different NDB's heard to date.

http://www.geocities.com/ko6bb/
Merced, Central California, 37.3N  120.48W  CM97sh