WW2 electronics AA delayed shells

[CatalinaWOW]

At least where I have worked in the US a fuze is a device to set off ordnance while a fuse is used to limit excessive current.  Don't know about world wide usage but nationalized spell check wouldn't help that since the program has no idea what you are talking about. 

The story of the VT fuze has always fascinated me.  VT stood for variable timing and was a bit of disinformation to conceal the fact that it was a proximity fuze.  Prior to this fuze AA shells had a timer which was set mechanically before firing.  Time delay chosen to go off when it reached the altitude the targets were expected to be at.  Obviously there are all sorts of problems with that, starting with knowing that altitude, convincing the targets to stay there, getting the poor guy loading the gun to twist his screwdriver the right way over and over again and following through to various times to altitude due to ammunition differences, air density variations and the like.  But as a partial answer to lordvaders original question these fuzes where purely mechanical.  A spring driven clockwork movement.  These movements were quite reliable and still used in safeing and arming applications well into the 1980s and 1990s.  But the whole infrastructure for that, from design through manufacture is gone now.  Too expensive without that infrastructure.

There were 13 manufactures for the tube used in the VT fuze.  They tested huge batches and found that only one relatively consistently survived the firing (when waxed into a hole cut in a wooden block).  I think I remember that Sylvania was the winner on that.

There was an optical version also developed, but it never worked out all that well.

The thing that really fascinates me about this fuze was how fast this got into production.  Tuves and team apparently got the concept in 1941 and 4000 units were built and tested at White Sands in early 1942.  Less than a year later they were at full production making 80,000 per week.  Pretty impressive ramp up for a totally new technology and working under the constraints of total secrecy.  Some folks say this was the second most secret project in the US, after the Manhatten project.  Shows what can be done when you really, really want to.

[jmelson]

well why do so many tubes need several hundred volts, why were these super low voltage tubes not used in radio's, tv, etc ?

They weren't really up to the job, & there was really no advantage in their use.

I have an R-392 receiver that runs entirely off 28 V DC, with no voltage converter.  All tubes are pretty standard-looking 7-pin miniature.  It works pretty well.  It was designed to run off a military truck electrical system.

Some later gear moved to 57xx series tubes that were even smaller, and ran on pretty low plate voltage.
Some of the 1960's crypto gear had hundreds of these tubes in one unit.

Jon

[james_s]

well why do so many tubes need several hundred volts, why were these super low voltage tubes not used in radio's, tv, etc ?

They were, well not those specific tubes but low voltage tubes were used in farm radios that ran off 32V. Tubes are less efficient at low voltages though, they are inherently high impedance devices so the current they can carry is limited. For a given tube if you use a higher voltage it can handle more power all else being equal. When you've got a wall socket available there's no reason to try to make a radio with a low plate voltage when you can have a much higher voltage available and get much better performance for the same cost in parts.

[jesuscf]

Very interesting.  If the enemy knew about this kind of fuze, wouldn't a radio receiver had detected an incoming projectile?  Once detected, wouldn't it have been easily activated with a radio transmitter?  It reminds me of what happened with the German magnetic mines.  Thunderf00t has a nice video about it:

[Canis Dirus Leidy]

If the enemy knew about this kind of fuze, wouldn't a radio receiver had detected an incoming projectile?  Once detected, wouldn't it have been easily activated with a radio transmitter?

"The method and system of this invention is a fuze jamming device which is effectually a repeating facility in which the continuous wave (CW) signal transmitted by the fuze is received, and retransmitted back to the fuze."

[schmitt trigger]

What I find incredibly fascinating about WW2 is the amount of technical and engineering achievements by all major belligerents.

And those were done in record time, and within the constraints of simultaneously waging a total war.


Back to the original topic.
There were several very low voltage tubes developed. My fave is the CK534AX. With an operating plate and filament voltages of 15 and 0.625 volts respectively, these were well within transistor power supply levels.

[Gyro]

It's because the parties were waging total war, not despite.

Winning a (conventional) war depends on outpacing the enemy in all things. That means that factories get re-assigned from their previous production to weapons etc. R&D goes the same way. Normal working hours, marketing overhead etc. go out of the window and everyone focusses on coming up with something new and getting it into use as urgently as possible.

Nothing unites a country in a common goal like all-out war (sadly).

[Mr. Scram]

What I find incredibly fascinating about WW2 is the amount of technical and engineering achievements by all major belligerents.

And those were done in record time, and within the constraints of simultaneously waging a total war.


Back to the original topic.
There were several very low voltage tubes developed. My fave is the CK534AX. With an operating plate and filament voltages of 15 and 0.625 volts respectively, these were well within transistor power supply levels.

Look at all the junk the world manages to produce on a daily basis and imagine all those efforts redirected into a war effort, with the added incentive of people working to protect their lives and everything they hold dear.

[chris_leyson]

After a little bit of research I'm sure I have a Mk45 Mod 11 fuze. According to OP-1480 https://maritime.org/doc/vtfuze/index.htm the approximate length of the Mk45 Mod 12 is 7.7", my fuze measures 8" when what is left of the rear section is screwed on. I think when they were deactivated they just chopped the back end of the rear section off with a band saw. The Mod 11 was longer and taken out of service.
I have the schematic drawn out but need to check the cathode connections for "top" and "bottom" filament connection.
Also have to check the capacitor orientations for outside foil. There are six capacitors in the amplifier section not counting the firing capacitor. Three of them are marked RCA TYPE M 0.004 MFD and the other three are marked 0.01 SELKAR S P12705.
It turns out that the "SELKAR" tubular capacitor was manufactured by Sprague from 1944 onwards for the US Navy, Sprague Electric Co. v. Commr. of Internal Revenue. What looks like a paper capacitor actually turns out to be metallized film, cellulose acetate.
The firing capacitor is maked M927654 1 MFD 100 V.D.C. FAST A8076. Best guess for B+ operating voltage is 67.5V because 67.5V dry batteries were available in the 40's and dry batteries were used in earlier fuzes. Ralph B. Baldwin's book mentions 67.5V dry batteries.