[ARC5] Heath GDO People

[Richard Knoppow]

    It seems to me I knew the history of the GDO but can't 
remember it. They were certainly popular in about the early 
1950s. I had a home built one long ago but it disappeard during a 
garage sale.
    I have a Millen tube GDO and an AN/APM-10. The military one 
is more elaborate but the Millen one is easier to use. It also 
has the advantage that it can test many crystals by connecting 
them in place of a coil. There is enough radiation to pick it up 
on a sensitive counter or certainly a receiver. The capacitor 
setting for maximum output gives some idea of the correct load 
capacitance for the crystal. Because the APM-10 has resistors in 
the plug-ins one can't put a crystal across the terminals to test 
it. Both are pretty accurate in calibration but the accuracy of 
the Millen surprised me. I do not have the accessory coils for 
the Millen but would like to find a set sometime.

On 4/25/2022 8:21 AM, Jack Antonio wrote:
> I have an EICO grid dipper, from my grandfathers estate, but have 
> since graduated to
> an AN/PRM-10.  The EICO was always a bit finicky in getting good 
> coupling to the coil under
> test.
> 
> Jack Antonio
> WA7DIA
> 
> 
> On 4/25/2022 11:10 AM, MICHAEL ST ANGELO wrote:
>> I built the solid state Heath HD-1250 GateDO. I remember 
>> soldering the leadless 47pF ceramic capacitors to the variable 
>> capacitor in the oscillator section. The foam turned to goop 
>> and I eventually removed it.
>>
>> I have the Millen 90651 GDO.
>>
>> I find both were useful in getting into the ballpark range of a 
>> resonant frequency but not useful in actually measuring or 
>> calibrating circuits or antennas.
>>
>> Mike N2MS
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL