[Test-Equipment] Millen GDO question

[Bill Smith]

----- Original Message ----- 
From: Richard Knoppow
To: ka4inm at tampabay.rr.com ; Discussion of Electronic Test Equipment
Sent: Wednesday, August 03, 2011 4:23 PM
Subject: Re: [Test-Equipment] Millen GDO question

    What I wanted to know was if this was normal behavior. I
will have to obtain a couple of fresh tubes and try them.
Even though the current tube tests good on a TV-7 it doesn't
mean it is good enough for this circuit. The meter reads
quite high on the other bands although it varies quite a bit
from one to another and across each. That I would consider
normal. I think the hair-pin coil is just fine, in fact
there is not much that could go wrong with it. The
frequencies are reasonably correct on all of the coils. I
think there was probably some sort of adjustment for this at
the factory but I am not about to fuss with it to try to
make it better than it probably was new.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com

Hi Richard,

Mine does the same thing.  I don't get much meter deflection with the
hi-band coil, although pinching the coil makes the meter drop, and it drops
out altogether at about the same spot as yours.

Your meter is likely working as designed.  Recall it is from a much simpler
era.  There was no coil calibration other than winding the coils to a
specified inductance.  Expect the oscillator to pull quite a bit during an
observed dip.  The frequency calibration chart inside the unit is
surprisingly accurate, but can only serve as a rough guide to the actual
frequency.

Accurate frequency measurements require a calibrated receiver, and with any
modern receiver with a digital readout the meter can be used to accurately
measure inductances and capacitance.  The easiest way is to combine a known
and unknown component in a parallel-resonant circut.  Accuracy is in the
eyes of the beholder, but certainally measurements can be made that are more
than accurate enough to build period transmitters and receiver circuts.

A grid-dip meter is a handy device to have in the shack.  It isn't the vital
component it once was, as modern antenna, inductance, and capacitance
bridges are often easier to use, but it still has its purpose and is fun to
pull out and use when needed.

The Millen here is happily stored near a working BC-221 frequency meter.

73 de Bill, AB6MT
hbco2 at sbcglobal.net