WW2 electronics AA delayed shells

[lordvader88]

In things like anti-aircraft guns, with exploding projectiles, How did they make delayed fuses and proximity fuses, sensor based fuses, fit inside the projectile, way back in WW2 and before/after using electronics ?

What kinds of circuits were they, surely they weren't making ultra mini vacuum types, or ultra mini high voltage batteries to fit in stuff like this, what kind of HV capactors maybe were used, or I wonder...etc ?
https://en.wikipedia.org/wiki/Proximity_fuze


I can imagine maybe using the voltages from the weapons, being set for a certain range, then loading a RLC tank circuit, that decays as the projectile travels for few seconds, then somehow triggering at some lower voltage from the tank circuit. What were they really doing and how and with what ?

[dmills]

By the end the AA shells were actual radar proximity fuzes.

Built with miniature valves and a rather clever battery that was activated when the acceleration of the firing broke a glass tube of acid.

There are diagrams (Including circuit diagrams) out there.

Incidentally, ground combat using these (very expensive) rounds in error was how they discovered the terrifying effectiveness of air burst rounds on infantry.

Google is your friend (But it helps if you spell fuze correctly). 

[vk6zgo]

In things like anti-aircraft guns, with exploding projectiles, How did they make delayed fuses and proximity fuses, sensor based fuses, fit inside the projectile, way back in WW2 and before/after using electronics ?

What kinds of circuits were they, surely they weren't making ultra mini vacuum types, or ultra mini high voltage batteries to fit in stuff like this, what kind of HV capactors maybe were used, or I wonder...etc ?
https://en.wikipedia.org/wiki/Proximity_fuze


I can imagine maybe using the voltages from the weapons, being set for a certain range, then loading a RLC tank circuit, that decays as the projectile travels for few seconds, then somehow triggering at some lower voltage from the tank circuit. What were they really doing and how and with what ?

The link you provided answers most of your question-------but, yes, there were very small vacuum tubes & gas thyratrons made at the time.
In fact, the link mentions this (ignore the reference to "all solid state" a couple of paragraphs in).

Miniaturised "high voltage" batteries (actually around 22.5 volts) were commonly used in tube type hearing aids immediately before & just after WW2, so the capability was available.

The proximity fuse batteries were probably less of a design problem than hearing aid ones, as flight times of the shell were very short, so neither the HT or "filament" battery needed a long life.
Shelf life is of course important in both applications.

If it was being designed today, it would almost certainly contain a microcontroller somewhere, but people have become so accustomed to being able to use "brute force" methods easily, that they cannot readily comprehend the "work-arounds" that allowed designers in earlier times to produce effective devices.

[vk6zgo]

By the end the AA shells were actual radar proximity fuzes.

Built with miniature valves and a rather clever battery that was activated when the acceleration of the firing broke a glass tube of acid.

There are diagrams (Including circuit diagrams) out there.

Incidentally, ground combat using these (very expensive) rounds in error was how they discovered the terrifying effectiveness of air burst rounds on infantry.

Google is your friend (But it helps if you spell fuze correctly).

Much of the world call them "fuses".
Google usually isn't very sensitive to US-v-"just about everybody else" spelling distinctions, & will normally bring up the same sites using both spellings.

[lordvader88]

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

[soldar]

By the end the AA shells were actual radar proximity fuzes. 

Can we have some cites corroborating that? Because I find it extremely difficult to believe.

I know AA guns were aimed using radar but those radars were the size of trucks so I would be very surprised to learn the shells had radar proximity fuses.

I would think they were timed fuses which were simply mechanic or chemical.

[dmills]

Here is a decent article https://warfarehistorynetwork.com/daily/wwii/artillery-proximity-fuses/

But a quick search on "ww2 proximity fuze" will turn up quite a lot of stuff including drawings and cutaways, these things were made for AA, Artillery, gravity bombs.

Arguably it was more RF proximity sensing then radar, but still.

Regards, Dan.

[vk6zgo]

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.
Analog TVs in particular, need to produce fairly serious power in the horizontal & vertical scanning circuits.
The easiest way to get such power is to use higher voltages & full sized tubes.

Conventional Superhet radio receivers used compound tubes in their mixer stages, which could both do the mixing and provide the local oscillator function.
Very hard to do with sub-subminiature tubes, as was the audio output requirement of, commonly, several watts.

The gain of even full sized tubes with low anode voltages was low, & it was not till the 1960s that tubes designed to operate with anode voltages of around 12v with enough gain to be used in the RF & IF stages of car radios were developed.(this allowed the car 12volt battery to run everything.)

Those radios had solid state audio output stages, as power was too hard to obtain with tubes at such low voltages, whereas power transistors were designed for such service.

[Canis Dirus Leidy]

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

In brief: more voltage, more power, less distortions:

(In the twenties, the Soviet industry produced ST-6 vacuum tube. Due to the use of an “accelerating” (with a positive voltage) cathode grid, and a small gain factor, the tube could work at an anode voltage of only 20 volts. But in general it was worse then R-5 at 100V of anode voltage).

Can we have some cites corroborating that? Because I find it extremely difficult to believe.

Just google "Mark 53 proximity fuze": https://www.radiomuseum.org/r/crosley_proximity_fuse_mk53_fuze.html

I know AA guns were aimed using radar but those radars were the size of trucks so I would be very surprised to learn the shells had radar proximity fuses.

These devices have different work distances. Tens of kilometers for air warning/fire control radar and tens of meters for proximity fuze.

[Gyro]

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

Low voltage directly heated tubes were used in many many battery portable radios. They used 1.5V filament and 90V (end voltage ~50V) batteries. They were capable of driving an efficient paper speaker at acceptable volume. Specialised tubes like Electrometer tubes have a maximum anode voltage of around 6V.

The problem with low voltage tubes - low power capability (although valve rectifiers and series voltage regulator triodes work at low anode-cathode voltage drop, not battery applications though). As for TV's, what would be the point, you need EHT to make a visible image on the screen, high drive on deflection coils etc.

[chris_leyson]

All of the US manufactured proximity fuzes used VHF doppler at around 150MHz or so, although I can't find a reference to confirm that. I powered up a Mk 45 fuze about 20 years ago at it seemed to oscillate at 120MHz. About 15 million Mk 45 fuzes were manufactured for the US army and about 1.6 million for the the British army, also about 80,000 Mk 45 (3"/50) were used by the US navy but suffered from premature detonation due to high waves when fired at a low angle, they were withdrawn from navy service and replaced with a five tube design with the additional tube used for AGC, possibly the Mk 53 or Mk 58.
The Mk 45 used three miniature triodes and a thyratron. A single triode VHF oscillator was mounted just under the antenna and a pair of triodes were used as the detector which triggered a miniature heated thyratron that was used to discharge a 1uF 100V paper cap into the squib.
The battery was made up of stacked annular discs, one side zinc and the other carbon, with plastic spacers and an amuple of chromic acid. The shock of gunfire would shatter the ampule and the spin of the shell would distribute electrolyte throughout the battery plates. It took about 1/10th of a second after set-back before the radio transmitter functioned.
Due to the high forces at set-back the valve structure would buckle slightly causing the tungsten filament to bend so a ruggedised tube was developed with a small "mouse trap" spring to keep the filament under tension.

Reference "The Deadly Fuze, The Secret Weapon of World War II" Ralph B. Baldwin ISBN 0 354 01243 6
US3113235 Rugged Vacuum Tube H.H Porter Etal
US3166015 Radio Fequency Proximity Fuze M.A. Tuve Etal

A poor picture of a pair of Mk 45 triodes posted below. Top tube is the oscillator triode and you can just see the grid support in the centre. Bottom tube is one of the detector triodes, the 'T' shaped structure to the right, mounted between the supports, has the "mouse trap" spring wound onto it.
Somewhere I have a schematic from a reverse engineered Mk 45 and will post it when I find it.

[vk6zgo]

By the end the AA shells were actual radar proximity fuzes. 

Can we have some cites corroborating that? Because I find it extremely difficult to believe.

I know AA guns were aimed using radar but those radars were the size of trucks so I would be very surprised to learn the shells had radar proximity fuses.

I would think they were timed fuses which were simply mechanic or chemical.

It wasn't really quite radar, but the free running oscillator in the fuse was affected by the proximity of other objects.
Apparently there was a reflected wave which was Doppler shifted.
This mixed with the local oscillator in the oscillator tube*, having more & more effect as the other object became closer, until it tripped the fuse.

This is the best translation I can make from the quite meagre information I found on the 'Net.

*It was not unusual to use tubes for several different functions, before the advent of compound tubes which separated the functions, offering better stability.
PS:- It seems the "production" version was more complex, as describes by chris_leyson above.

[chris_leyson]

Radar was never used in WWII proximity fuzes. The Doppler signal from a reflecting target was detected by measuring the variation in oscillator anode current as the shell approached the target. I think typically they were designed to detonate at 50 feet or so from the target but there were lots of variations depending on the application. If used to shell fox holes as in the Battle of the Bulge I think the optimum burst height was 70 feet, the German army didn't know what had hit them. They were also very effective against the V1 with help from the M9 gun director and SCR-584 radar.  A real Mk 45 shown below (inert).

[dmills]

Sure sounds like CW Doppler radar to me, especially as they shaped the radiation pattern and amplifier responses to make the range/velocity sensitivity match the shrapnel pattern.

Radio ranging certainly, and if a modern microwave doppler door opener can be described as  a 'radar' sensor, and I have seen them described that way, then that surely qualifies? 

Regards, Dan.

[soldar]

Thanks for the very interesting information. Those WWII fuzes were more advanced than I thought.

[lordvader88]

By the end the AA shells were actual radar proximity fuzes. 

Can we have some cites corroborating that? Because I find it extremely difficult to believe.

I know AA guns were aimed using radar but those radars were the size of trucks so I would be very surprised to learn the shells had radar proximity fuses.

I would think they were timed fuses which were simply mechanic or chemical.

It's ture, and it like to see a schematic

When they 1st made radar, they where trying to detect reflections, at a few miles, that where about 100-1000 times stronger Watts/area than a typical radio of the time used, around micro-Watts/meter^2 iirc

So in some projectile, that's getting within 10-50 meters or whatever, the radar EM is way way stronger. But what all is the circuitry and what parts/etc ??

When 'they' 1st started making spark gaps that would pick up EM waves, did they in-effect miniaturizes that, so that it sets off some primer cap ?

[chris_leyson]

From Merle A. Tuves patent US3166015

"With the oscillator 35 energized, as the projectile approaches a target, such as an airplane, the radio waves emanating from the projectile are reflected by the target, and the reflected waves change the radiation resistance of the antenna 33. As a result, the loading of the oscillator 55 circuit is changed, whereupon the plate current of the tube 40 also changes. This current change in the plate circuit develops a voltage across resistor 50 which is impressed upon the amplifier 36 through the resistance 52 and a wire 78 connected through a plug-and-socket connection 79 to one side of a condenser 83 in the amplifier unit. The other side of the condenser 83 is connected to the control grid of tube 84, the resistance 82 providing proper grid bias. The condenser 80 serves to by-pass high frequencies to the ground and cooperates with resistor 52 to form a low pass filter.

The amplifier, as shown, is provided with a second stage of amplification, including a tube 85, and the output of the amplifier is used to trigger a thyratron 86."

Maybe it could be argued it's very primitive CW radar but I would say it's more akin to a proximity detector. As the patent was filed January 1943 it's probably an early example of a proximity fuze. Must go and find that schematic. 

[Mr. Scram]

It always boggles my mind that a place as violent as an artillery shell can carry electronics without destroying it before final detonation. The fact they managed to do this that long ago without the benefits of ICs is the cherry on top.

[dmills]

The electronics is not hard, making the electronics work in a shell acceleration environment in a way that is sufficiently squaddie proof and safe to abuse, that is tough (Also, at least reasonably sea water resistant). Actually a big part of the real magic was the power source for the thing which had to come up to power quickly (~0.1 seconds) and have a shelf life of years.

There were issues with firing at low angles over rough seas where the the waves could be detected and cause detonation, they fixed this with a diode detector producing a bias to the trigger circuit.

The design is an awesome mix of physics, chemistry, electronics and mechanical engineering.

[radar_macgyver]

Much of the world call them "fuses".
Google usually isn't very sensitive to US-v-"just about everybody else" spelling distinctions, & will normally bring up the same sites using both spellings.

Professional publications about explosives and munitions distinguish the "fuse" and "fuze" spelling. The UK Ministry of Defence states (emphasis in original):

    FUSE: Cord or tube for the transmission of flame or explosion usually consisting of cord or rope with gunpowder or high explosive spun into it. (The spelling FUZE may also be met for this term, but FUSE is the preferred spelling in this context.)
    FUZE: A device with explosive components designed to initiate a main charge. (The spelling FUSE may also be met for this term, but FUZE is the preferred spelling in this context.)

https://en.wikipedia.org/wiki/Fuze

[iMo]

The projectile rotated 3000 rev/minute, and the antenna had a special radiation pattern.
While in proximity to the target it created a beat, the beat was amplified and triggered the fuse. So no Doppler, afaik.
The fuses were easy to trigger far from target by sending modulated signal and sweeping around the frequency (around 200MHz). That was proven during US experiments in late '44 as the large amount of fuses were captured by Germans after D-day and US military was looking for potential countermeasures.

[Cyberdragon]

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

Low voltage directly heated tubes were used in many many battery portable radios. They used 1.5V filament and 90V (end voltage ~50V) batteries. They were capable of driving an efficient paper speaker at acceptable volume. Specialised tubes like Electrometer tubes have a maximum anode voltage of around 6V.

The problem with low voltage tubes - low power capability (although valve rectifiers and series voltage regulator triodes work at low anode-cathode voltage drop, not battery applications though). As for TV's, what would be the point, you need EHT to make a visible image on the screen, high drive on deflection coils etc.

Subminiature tubes were used a lot in the military were applicable from walkie-talkies to radar control systems. They weren't often used in the consumer market, but there were things like pocket radios and hearing aids that used submini tubes.

https://www.radiolaguy.com/Showcase/PortableRadios/subminiature.htm

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.cia.gov/library/readingroom/docs/CIA-RDP80-00809A000600330387-6.pdf&ved=2ahUKEwjugLOc5rvhAhWDct8KHelKDV8QFjANegQIBhAB&usg=AOvVaw2OXeQISlvzVe04eLA-4yg3

They were also used in some calculators and computers.
 
https://www.radiomuseum.org/forum/subminiature_tubes_in_computers.html

Note: these tubes operate like a normal vacuum tube, unlike the low voltage car tubes which were space charge tubes.

[apis]

[chris_leyson]

I think Merle A. Tuves patent is probably for the Mk 30 or maybe Mk 32 fuze for 4.5 inch AA guns. The Mk32 required separate oscillator and amplifier sections which made it quite long and it also required a 2 inch dry battery.

Early fuze designs used 67.5V dry batteries which were also used in some WWII walkie-talkies, however, it was found that the shelf life was as short as 3 to 4 months in the south pacific, but in general was 6 to 12 months. National Carbon Company, a division of Union Carbide, set about developing a reserve "wet" battery. The reserve batteries were made up of stacked zinc/carbon annular rings around a small glass ampule containing chromic acid. The ampules were supported by a "crown" breaker or a "Bellville washer" in the 1.5 inch batteries and a "two point" breaker in the 2 inch batteries. As the centrifugal forces in a spinning the shell were so high it was possible to have a dead section in the battery if the electrolyte was not uniformally distributed. To fix this 1/64th inch holes were drilled into the battery plates so that the amount of electrolyte reaching each plate was equalized. It was considered preferable to allow a high resistance short through these holes than to risk complete fuze failure through improper electrolyte distribution. The same production lines that made Christmas tree lights were used to make ampules - hence no Christmas tree lights for the duration of the war. Eastman Kodak did a lot of work on the battery design alongside National Carbon and spent a million man hours on production methods and tooling before producing a single battery. On V-J day, Nation Carbon, Eastman-Kodak and Hoover were producing 101,000 batteries per day.

[lordvader88]