Tuned Circuit Selectivity

If it's a Model 59, it's a beautiful thing.

Cheers

Phil Hobbs

Nice work! I do actually own a bespoke, discrete Q-meter which is about the size of a modern oscilloscope. I can see it from the distance but can't get anywhere near it owing to it being surrounded by 'moat' of other vintage test equipmnent. I'd post a pic, but I don't have a telephoto lens to hand, nor do I have a photo hosting site ATM either. Shame, really must do something about that. How do you rate Dropbox?

What methodology are they using to measure these very low capacitances?

Well, *if* that isn't the one I have it's identical in appearance at least. I'll have to get it out properly for comparison purposes and have a play with it this weekend coming.

Thanks, Phil.

There are manuals online, with schematics.

Basically they apply a 1 MHz sine (sometimes other freqs on different models) to one end of the cap and measure the current on the other end, with RF circuits and amps and a phase-sensitive detector. Lots of RF gain gives sensitivity.

Dropbox is free, with 2 or maybe 4 Gbytes. I have a terabyte, for something like $8 a month. I use it to work from here to home to the cabin to the laptop, instead of carrying memory sticks around. I do the cabin monitoring and temperature controls through a shared Dropbox folder too.

DON'T throw it away! I'll buy it for a reasonable price.

Darned right.

A few years ago I did a bake-off between several dipmeter I own or could borrow: my Model 59, a B&W 600 (tube), a Heathkit solid state (the 1250 I think) and their HM-10 tunnel-diode dipper, and the "dip meter" plug-in coils for an MFJ 1259. The "test subject" was a section of Airdux inductor, wired to an air-variable capacitor... should be a nice high-Q resonator.

The goal was to see how far away from the test coil I could hold the dipmeter probe-coil, and still get a readable "dip" at the resonant frequency. The further away, the less coupling and "pulling".

The MJF coils were essentially useless... couldn't get a meaningful dip unless the coil was touching the test coil, or nearly so, and it wasn't particularly stable or easy to read.

The HM-10 was almost as bad.

The Heathkit 1250 could get a dip from an inch or two away.

The B&W did a bit better than the 1250.

The Model 59 was getting a detectable dip from 4-5" away. Very, very good sensitivity.

I'd love to test one of the Millen GDOs but the only times I've seen one in decent condition, for sale with its various coils, the price being asked has made me back away slowly.

Would $3,900 be reasonable? An Ebay seller is offering a set with the LF and MF heads as well as the more common HF/VHF head.

piglet

The Boonton 72 measures the capacitance between the two test terminals while rejecting stray capacitance to ground which is neat.

I only need to use it once or twice a year but it is unbeatable.

piglet

It's great for semiconductor C-V curves.

I have one of those too, but I've never turned it on. I'll give it a try when I have a chance.

Cheers

Phil Hobbs

I paid $135 for one of the HF/VHF and $120 for the UHF one. They work perfectly.

Cheers

Phil

I paid $81 for it with a complete set of coils.

Cheers

Phil Hobbs

What on earth makes you think I'd throw it away??

I've had a chance to examine it further today and it's the same as Phil posted about, Model 59 with the pluggable coil set, mint condition, amazingly. No plans to sell it for the foreseeable future. Don't need the money. Got money, want time.

Seems a fair price to me. If we were living in 2040, that is. Some people are just plain greedy.

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