Oddball Raytheon Subminiature QF-721 tubes

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Proximity fuses are not usually Doppler, but pulse coincidence instead.

In the first two pages of 25 items each, I didn't see a single thing that even looked like a tube, let alone a subminiature.

Thanks, Rich

In other words, you couldn't find a pig in a dishpan.

Out photos ARE almost always of the actual item. Otherwise they are a representative of a quantity available. Or, rarely, exceptions are clearly labeled.

-- Many thanks,

Don Lancaster voice phone: (928)428-4073 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss:

Please visit my GURU's LAIR web site at

Proximity fuses are not usually Doppler, but pulse coincidence instead.

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That probably amounts to the same thing in that particular application.

I was simply quoting how it was described to me by someone on A.B.S.E

The internals aren't very clear, but, AFAICS, it looks very like diode structure.

Proximity fuses are not usually Doppler, but pulse coincidence instead.

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Wikipedia seems to agree with what I had previously been told:

Its a sort of crude form of doppler discriminator, as the shell approaches the target to the point that sufficient wave energy is reflected to interact with the original oscillator, the reflected wave is apparently faster than the one transmitted.

The doppler effect so produced makes the reflected wave go in and out of phase with the original oscillator, as the distance shortens the reflected wave gets strong enough to produce a low frequency beat - this is what is amplified to trigger the thyratron.

There is an element of pulse coincidence, but the doppler effect causes it to alternate between constructive and destructive interference.

Of course not, if the dishpan is full of cats and snails.

In other words, go f*ck yourself.

Thanks, Rich

For your sake I hope you are being sarcastic :-)

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Think through what the two techniques measure and how that relates to the proximity of the shell to the target.

?-)

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Sort of a simple metal detector. That seems to work too.

?-)

Left column, click on "vintage electronics".

Sort of a simple metal detector. That seems to work too.

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All the metal detectors I've seen, the proximity of metal alters the inductance of one or more search coils - I've yet to see one sensitive to the velocity of the target.

The circa-1960s Hawk RADAR sets that I worked with in the Army were loaded with 100's of subminiature tubes. About 400 per unit. Most of them were used in applications and with voltages and signals that were usually being performed with miniature tubes. Construction-wise what internals that could be seen resembled a minature tube with most of the empty room and spacers taken out. If memory serves a dual diode was the only type with more than one function. I'm drawing a blank about dual triodes. The subminature tubes were rated to be highly rugged (they were also used in missles and artillary shells) and long-lived - at least 10,000 hours. In the equipment I worked on they were clipped onto heat sinks that underlaid the swaged-post epoxy terminal boards that the other parts and wireing were attached to. The chassis were like 19" long sheet cake pans and mounted as back-to-back pairs in pull-out drawers. Air was forced in between the chassis. The chassis were held in place by aircraft-style screw clip fasteners and all connections were via a single multi-pin connector with both shielded and unshielded pins and teflon-coated silver-plated fine stranded wiring.

The filament supplies were magnetically-regulated 6.3 volts DC while the B+ was highly regulated 250 or 300 volts. The few socketed tubes were power tubes including 300A series regulators in the power supplies. Air temperature inside the equipment boxes was up to 140 degrees.

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I guess you did not read the article all that carefully, Both VT and Doppler are misdirectors.

?-))