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Antique Electronics Autopsy: Heathkit Grid Dip Meter GD-1A

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kfield
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My cousin had one!
kfield   11/27/2013 12:25:20 PM
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Very cool - I remember my older cousin owning one of these, and he was very stingy about letting the other kids touch or play with it. Where did you find one, and I bet you paid more than $20!!

Caleb Kraft
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Re: My cousin had one!
Caleb Kraft   11/27/2013 1:05:33 PM
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I think I actually paid $20! 

David Ashton
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Re: My cousin had one!
David Ashton   11/27/2013 9:57:07 PM
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Pity you did not get the coils Caleb, I daresay it would work still.....

I have a friend who is a "ham" and he wanted me to help him make a GDO.  I found a nice circuit with a FET that does from the 100's of KHz up to the mid 100's of MHz.     If it works, maybe I should get into the kit business.....

grg9999
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Re: My cousin had one!
grg9999   11/28/2013 12:05:02 PM
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I had one of these years back.   Very useful gadget.  It's basically an RF oscillator with a grid current meter.  So you can use it as a signal generator to test out radios and the like.  And since it has a grid-current meter, you can put it next to a L/C circuit and you'll get a "Dip" in the grid current at resonance, so you can verify the working and frequency and approximate "Q" of a tuned  circuit.  very useful, as old radios had a lot of tuned circuits.  If you dial back the knob until it just stops oscillating, it becomes a tuned RF voltmeter, very useful in debugging and tuning up live oscillator and transmitter stages.    All of the frequency and voltage and stability aspects were very approximate and not going to put Boonton or HP out of business, but good enough for many purposes.    Heath made a smaller, newer one years later using transistors and tunnel diodes, but they were not as good as this old tube-based one.   You just could not get as good a "dip" with those low-impedance transistors and tunel diodes.

 

 

zeeglen
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Re: My cousin had one!
zeeglen   11/29/2013 10:44:03 AM
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>Caleb " I think I actually paid $20!"


Love these old Heathkit teardowns!  One minor correction, the bottom slide switch is actually the diode/osc mode select; the power switch is on the sensitivity control.  In diode mode the B+ to the tube plate (anode) is turned off, then the unit could be used as a wavemeter or AM demodulator into the headphones due to rectification between the grid and cathode.


I bought a used successor the GD-1B from a fellow ham while in high school.  Think I only paid $15.  Still have it, and will email you a photo of the plug-in coil set.


w2aew
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More on the Dip Meter...
w2aew   11/27/2013 1:04:23 PM
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If you are curious about how you'd use a Dip Meter, check out my video on the basics of Dip Meters.  In the video, I use a Heathkit Dip Meter, but it is a more modern, solid state version that I built as a kid in the 70s.  

http://www.youtube.com/watch?v=_HwIL6mqq_k

 

Caleb Kraft
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Re: More on the Dip Meter...
Caleb Kraft   11/27/2013 1:05:49 PM
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Oh cool, thanks for sharing that!

junko.yoshida
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Re: More on the Dip Meter...
junko.yoshida   11/27/2013 1:14:52 PM
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@w2aew, thanks for posting the youtube clip. I had NO idea how people would use one of those devices until I saw the video!

Susan Rambo
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Re: More on the Dip Meter...
Susan Rambo   11/27/2013 2:45:28 PM
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Thanks for posting the Heathkit Solid-State Dip Meter video. Very cool.

Bert22306
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Re: More on the Dip Meter...
Bert22306   11/27/2013 3:55:03 PM
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At first, I wondered how you were measuring the resonant circuit by only connecting to one point. And then I concluded you were actually measuring an antenna.

Interesting. A poor man's oscilloscope and oscillator all in one.

w2aew
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Re: More on the Dip Meter...
w2aew   11/27/2013 4:05:43 PM
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The only "connection" is inductive.

Bert22306
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Re: More on the Dip Meter...
Bert22306   11/27/2013 4:15:53 PM
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"The only 'connection' is inductive."

Okay, that too. But in order to measure the change in current through the resonant circuit, or voltage change created by a changing current flow, you need current to flow through the circuit under test. The flow was created because the circuit was radiating RF.

Sanjib.A
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Re: More on the Dip Meter...
Sanjib.A   11/30/2013 12:15:33 PM
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Cool video!! Are these instruments still in production? If I can find I would try to grab one and would like to experiment for debugging EMI/EMC issues.

w2aew
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Re: More on the Dip Meter...
w2aew   11/30/2013 2:22:48 PM
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There are probably not many being made these days. But MFJ Enterprises is still selling one http://www.mfjenterprises.com/Product.php?productid=MFJ-201

Sanjib.A
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Re: More on the Dip Meter...
Sanjib.A   12/1/2013 12:15:45 AM
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Okay...thanks a lot!

David Ashton
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Re: More on the Dip Meter...
David Ashton   12/1/2013 3:57:57 AM
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@Sanjib....if you want to be brave (and have fun) and make one yourself there is what looks like a very nice design here

http://sm0vpo.com/use/gdo.htm

80 KHz to 460 MHz - covers a good range.  I have not yet built one but it is on my to-do list....

Jonathan Allen
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Grid dip meter
Jonathan Allen   11/27/2013 1:08:11 PM
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As a power RF specialist I depedn on my trusty grid dipper.  Mine happens to be an Eico 710.  It's basically similar to the Heathkit shown but a bit more compact.  I carry it in a canvas case originally made for a "brick" cell phone.  The instrument and its coil set (The coils live in a mahogany block drilled to accept the pins.) fit perfectly.  There is even room for a spare tube, a BNC coil adapter, and the Manual which fits in its own zippered compartment.  I previously owned a solid state immitation "grid" dip meter, but it was almost useless so I traded it. 


In addition to analyzing resonant circuits, the GDO can test transmission lines for electrical length and measure the distance to shorts or opens.  As a wavemeter it detects RF leakage.  Amazing versatility for an instrument with just one triode section.  I won't leave home without it!

Susan Rambo
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Re: Grid dip meter
Susan Rambo   11/28/2013 11:41:58 AM
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Very nice, @Jonathan Allen. Would you paste some images of it in the comments so we can see your Eico 710? Thanks!

vvc0
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Fond Memories of Heathkit
vvc0   11/27/2013 1:33:49 PM
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I built a few Heathkit devices, including a color television, an oscilloscope, and a printer. Heathkit did an extraordinary job of design in putting together their kits. The assembly documentation was second to none. The color television had at least 5 or 6 manuals, covering the assembly of the circuit boards, the mechanical assembly of the unit, tuning the varius stages, and adjustments to the set. It was a marvelous way of gaining experience in assembly and testing of complex devices. I don't think there are any equivalent systems today that even come close to the experience Heathkit provided.

robotgrrl
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Heathkits!
robotgrrl   11/27/2013 8:07:30 PM
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Sweet photos of the insides of this Heathkit! It's really neat to see all of the old components and a tube!

 

I had the honour to start building an AC Voltmeter Heathkit when I was an artist in residence at Evil Mad Scientist (part 1, part 2). It was very interesting to build it, especially since Heathkits are recalled as legendary. It was cool having all of the wires being attached in 'mid air', compared to kits now where everything is on a pcb. Was definitely surprised at the amount of solder needed, since the 'lugs' were giant, as well as the leads from the components. Sometimes the instructions were confusing — but it's not like they could go and edit the documentation, since it's printed on real paper!

 

One of the pieces was missing, so we designed and laser cut a replacement part. People have actually downloaded the part from Thingiverse, so maybe there are other people out there who were also missing it (though unlikely)!

 

Noticed the 'mighty' capacitor in your GD-1A. There were also huge capacitors in the AC-VM, the metal enclosed one took up a lot of space. Why were capacitors so big back then? Were they made by hand or something?

David Ashton
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Re: Heathkits!
David Ashton   11/27/2013 9:49:28 PM
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@robotgrrl....    "Noticed the 'mighty' capacitor in your GD-1A. .... Why were capacitors so big back then?"

They have decreased a bit in size, especially high voltage electrolytics....think it;s something to do with the etching of the foil plates - and thinner foil.

But smaller is not always better - as I once found out:

http://www.eetimes.com/author.asp?section_id=36&doc_id=1284545

Bert22306
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Re: Heathkits!
Bert22306   11/27/2013 11:41:22 PM
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I too noticed all those "flying" components. That's the way most tube circuits we designed, I'd say until the 1960s perhaps. That's when you started seeing PCBs, even in some tubed electronics (miniature tubes mostly).

I bought a Knight Kit VOM way back Freshman year in college, and am still using it to this day. No tubes. Just passive components hanginmg out in mid air, as it were.

Michael.Thomas_#5
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Re: Heathkits!
Michael.Thomas_#5   11/28/2013 4:54:26 AM
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Early PCBs made with paper and phenolic or glue broke down under high voltage. No arcing or leakage over 1" of air.

Some military designs used a half-way system of epoxy boards with solder wrap posts. Made flying components a bit more controlled.

Cremo0
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Frequency range
Cremo0   11/28/2013 3:53:50 AM
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The frequency range covers 2MHz to 250MHZ

ANON1249426187345
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"Display"? That's what we call a meter, sonny..
ANON1249426187345   11/29/2013 1:28:24 PM
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Now you're making me feel old.  What you call a "display" is a "meter", which is short for "galvanometer", but I don't think anyone called them that after the dawn of radio.  Permanent magnet and a coil of very fine wire.  Current through the wire makes a magnetic field which moves the needle. 

The GDO's meter has only a single scale, but meters used in VOMs and VTVMs often had several scales for various ranges.  You had to be sure you were looking that the correct one.  But we were used to that from negotiating the multiple scales of our slide rules...  Some meters (such as my 1970-vintage Olson VOM) had a strip of mirror on the surface with the scales, so that you could line up the needle with its image and avoid parallax errors in your reading.

Regarding the "gigantic" capacitor - that one's actually pretty small (as implied by the "mighty midget" name) - only 15 uF and 150 volts.  Capacitors in the TVs I took apart in my youth often had electrolytics with voltage ratings up to 450 or more.  Often the "cans" were 1.5 to 2 inches in diamaeter and 3 or 4 inches long and contained three or four capacitors.

Note the capacitance is given "MF", using "M" for "micro" rather than the Greek letter mu.  Small capacitors were specified in "mmf", or "micro microfards", rather than todays picofarads.  Instead of nanofarads, you had values like "0.001 MF".  Luckily, there was plenty of room on the parts to print this sort of thing.

Jonathan Allen
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Grid dip meter
Jonathan Allen   11/30/2013 1:26:18 PM
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For anyone who wantsa to learn more about the grid dip meter, let me recommend a book:  "Servicing with Dip Meters" by John D. Lenk.  Howard W. Sams Co, 1968.


The Radio Amateur's Handbook also discusses this versatile instrument. 

 

 

xwindowsjunkie
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Wait a minute!
xwindowsjunkie   11/30/2013 3:23:30 PM
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I'm still using mine. It's not an antique, because if it is then I'm...........


Yes I built mine. It was the second Heathkit I built. It still has the original 6AF4 in it but the selenium rectifier has been replaced with a silicon diode and the power filter cap as well. 

I remember seeing a few articles way back then that had conversions detailed to put JFETs in place of the triode. One even went so far as to replace the power transformer with a basic 12.6/6.3 filament transformer so you could eliminate the high voltage (at least on the secondary side).

Jerrysc
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Grid dip Meter
Jerrysc   12/1/2013 11:17:48 AM
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Mine was a slightly later tube model. Looked the same except the meter bezel was transparent. Pulled it out after many years of storage and it was still in working order. Dont really have a use for it anymore so I sold it on eBay for $25.

grover_gren
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Re: Grid dip Meter
grover_gren   12/2/2013 10:00:39 AM
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Well done mister C you have found another monster! A truly scary-looking lump of hardware that deserves to be torn down and buried in ten different places. It looks like something reclaimed from the chamber at Abu Ghraib. Did I spot a half-hitch tied in the mains cable to provide strain relief? Nasty nasty. KILL IT WITH THE BIG HAMMER!  

mhrackin
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Re: Grid dip Meter
mhrackin   12/9/2013 3:26:00 PM
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Believe it or not, back in the '50s the "electrician's knot" was the CODE REQUIREMENT for power cord strain relief! Usually used with a rubber (natural of course) grommet that prvided a cushion between the CLOTH insulation and the nasty sharp edges of the hole in the sheet metal.  While on the topic of ancient history, the moving-coil meter movement had a name (eponymous with the inventor): D'Arsonval.  I still have quite a few Bakelite "terminal strips" for the RIGHT way to do the point-to-point wiring; flying connections were amateurish (no slur on hams, BTW; I've been licensed since 1957, ARRL Life Member).  Also ground lugs, along with some military-grade insulated standoffs for the same purpose as the strips (but single-point with a turret top compared to the multi-point terminal strips).  Despite the relative fragility of the vacuum tubes, the rest of the typical constructions of that era were pretty rugged, as they had to be with several hundred volts and high currents everywhere.

grover_gren
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Re: Grid dip Meter
grover_gren   12/10/2013 9:17:47 AM
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thanks for that comment mhrackin. D'Arsonval was an interesting chap, and what a time to work in science (1851 - 1940)

biassetting
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Anyone have the coil data for this Gd-1A??
biassetting   3/25/2014 2:36:35 AM
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I have been looking for any coil data that I could build replacement coils from. If anyone has the coil data and and a suitible diode replacement for the rectifier I most certain lt would appreciate the help.  Thanks

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