Needed Info: 100-250 Coil, GD-1B

[Dick Blaney]

More on the Heathkit GD-1B GDO.  To answer some of your other
questions, Calibration?  The kit came with the marked "generic" dial,
and one or more "blank" dials, ie; with the 0-100 logging and unmarked
range scales.  You would then use a signal generator of some sort, and
calibrate the blank scale.  Otherwise, like most builders, you would
simply install that "generic" scale, and be close.  After all, a GDO
was never meant to be a Frequency Meter.  Now, the 2 micas that
connect one to the plate, the other to the grid, thd the other ends of
each go to opposite ends of the tuning capacitor.  These are listed as
90 mmfd, (mmfd=pf).  About the cathode resistor, I see no reason to
jumper out that 100 Ohm cathode resistor.  It should be bypassed with
a 33 mmfd ceramic capacitor, though.   With respect to the tube, it
could be either a 6AF4 or a 6T9, according to my manual.  Mine has the
6AF4.  I see no reason to try to change mine to a FET, since the tube
gives me the acceptable performance that I expect from a GDO.  Hope it
helps.
73 de
Dick, WB8MHE
wb8mhe at bright.net

-----Original Message-----
From: al winfrey <awinfrey at iquest.net>
To: HEATH at LISTSERV.TEMPE.GOV <HEATH at LISTSERV.TEMPE.GOV>
Date: Saturday, June 26, 1999 4:15 PM
Subject: Re: Needed Info: 100-250 Coil, GD-1B


>Hi Steve,
>
>That coil is the one that always falls out when you open the box. If
I remember right ,
>it is just a "hairpin loop" made from 12 or 14 ga wire and having a
length of maybe 3 cm
>or a little over an inch.  It would be nice if someone else having an
actual coil could
>give you the exact measuerments.  You could adjust the calibration by
squeezing the coil
>a bit.  Hope that helps.
>
>Al - wa9hsl
>....
>
>Steve Harrison wrote:
>
>> Howdy,
>>
>> I've obtained a great-condition GD-1B from a very kind fellow in
>> Connecticut; but it is missing the 100-250 MHz coil and manual. I
probably
>> don't need the manual too badly (there isn't much to a GDO, after
all!);
>> but I would like to try to duplicate the original 100-250 MHz coil
if
>> possible. Also, I'm curious about any alignment instructions that
Heath may
>> have had (so the manual might be useful, after all). And, I found
the
>> original 82-ohm cathode resistor shorted with a jumper for some
reason. I
>> want to get this thing halfway calibrated and working on the
100-250 MHz
>> range in particular to give to a good buddy in Maine so he no
longer has
>> reason to complain "I can't tell if it's oscillating, nor where, if
it is!".
>>
>> SO: can anyone describe to me what the original 100-250 MHz coil
looked like?
>>
>> And, can anyone briefly describe any alignment instructions?
>>
>> And, was shorting that cathode resistor some mod to enable more
consistent
>> oscillation across the V/UHF range, or what?
>>
>> Also, what is the claimed value of the two mica DC blocking
capacitors
>> between the tube grid and plate, and the tuning capacitor??
>>
>> Finally... does the 6AF4 tube have to be in especially-good
condition in
>> order that this GDO operates reliably across the entire range? I
recall the
>> 6AF4 was used extensively as the local oscillator in UHF tuners
some 30-40
>> years ago, pre-Nuvistor days. I'm half-tempted to try a FET since I
don't
>> have any 6AF4s left (got lots of acorns for my own Measurements
Corp.  GDO,
>> though!).
>>
>> TNX Much,
>>
>> Steve K0XP
>>
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