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.....
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.
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.
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.
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.
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!
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.
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?
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.
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.
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).
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.
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!
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.
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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