FX-6A flashtube availability and data

The EG&G FX-6A xenon flashtube is used in the General radio Strobotac,
which is used to measure the speed of machines rotating at up to 25,000
rpm.
The FX-6As darken with age, and are hard to find.
FX-6A is an old EG&G product. The relevant part of EG&G was sold to
Perkin-Elmer
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, and P-E now makes
these flashlamps. I think that this is still done in Salem, Mass.
I talked to P-E today. The FX-6A is available for US $232.00 each for 1
to 10 units. FX-6 series are called "low cost strobes"; I don't want to
know what normal and high cost means.
They also sent me a FX-6A datasheet (well, max operating conditions):
Max energy per flash: 5 Joules.
Max average power: 7 watts.
Max anode voltage: 1000 Vdc.
Min anode voltage: 300 Vdc. (Typical will be ~600 Vdc.)
Max flash rate: 500 flashes per second (30,000 rpm).
Arc length is 7.9 mm. The trigger electrode (called the "sparker" is
near to the anode and cathode, inside the glass envelope. The required
voltage and energy was not documented.
Joe Gwinn
Reply to
Joseph Gwinn
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"Joseph Gwinn" wrote: (clip) The FX-6A is available for US $232.00 each for 1 to 10 units. (clip) ^^^^^^^^^^^^^^^^ Holy crap! I have an old Strobotac that I bought years ago for $5 (I think.) Care to make me an offer?
Reply to
Leo Lichtman
According to Joseph Gwinn :
Hmm ... where my wife was born (though not in the P-E plant. :-)
####### ### # # # # #### # # ### # # # # # # # # ### # # # # # ###### # # # # # # # # # # # # # # # # ### ####### #### #### # # ###
(The above should be viewed with a fixed-pitch font like Courier. If you don't want to take the time to switch fonts, it simply says "Ouch!" in *big* letters. :-)
That means that the batch of four which I won on an eBay auction is worth $928.00.
They were made May 22 1975 according to the stamp on the box endflap.
O.K. Which probably determines the choice of max RPM on the Strobotac.
Actually -- there are five of them, One (pin 1) is very close to one electrode (pin 9), and the remaining ones are equally spaced, with the final one not being nearly as close to its electrode.
But this suggests that they fire at much lower voltages than the typical trigger wrapped around the outside of the typical flashlamp.
Hmm ... A pity that it is not documented. That could be one of the factors which would make a normal flashlamp not suitable for the circuit in the Strobotac.
Thanks for digging up this information.
If nothing else, it makes me feel better about spending a bit over $125.00 for the batch of four of them -- and now I understand the motivation of the winning bidder in the batch which I *lost* prior to that. :-)
Enjoy, DoN.
Reply to
DoN. Nichols
Thats an outrageous price! - depending on the mechanical fittings, it SHOULD be possible to use a "standard" flash tube (their about $5 here) - you would need to get a trigger transformer and add a wire wrapped around the body to trigger them, but hey.....worth a try - might be other considerations, would need to dig out the data sheets and see.
Andrew VK3BFA.
Reply to
Andrew VK3BFA
formatting link
is a link to the typical tube I was talking about.
Reply to
Andrew VK3BFA
Looks like the ones used for dance-floor lighting- have you tried a stage equipment shop?
-Carl
Reply to
Carl Byrns
Ten dollars?
If I get a Strobotac, I'll be real motivated to do the engineering to find and/or fit a substitute flashtube.
Joe Gwinn
Reply to
Joseph Gwinn
I wonder if P-E is actually making the tubes these days, or selling new old stock one tube at a time.
I also wonder if the Russians have duplicated the FX-6A. They still make pretty good vacuum tubes, and I would not be surprised if there was a Soviet-era copy of the Strobotac.
Yes.
Apparently, all but the one designated as the sparker are used only as probes. No idea what is being probed for, or why.
Pin# - Use 1-3 - probe when required 4 - Anode (ie, positive) 5 - open 6 - probe when required 7 - Probe (no "when required") 8 - Sparker (will most likely be positive wrt the cathode) 9 - Cathode (ie, negative)
Yes, by a factor. The current Series 1100 tubes should give us the needed voltage range range, although the 1100s only go to 300 Hz.
One clue is that the max anode voltage is 1,000 volts. The sparker voltage will be in that range, as the sparker is simply another nearby electrode, albeit one not designed to handle the full flash energy. Typically, an internal trigger takes less than the full holdoff voltage.
I recall that the flash capacitors are charged to 600 volts; don't know where I got that tidbit.
A little reverse engineering is in order. Can you measure the trigger capacitor voltage and capacitance in your Strobotac? This will tell us the needed trigger energy.
Does anyone have a circuit diagram?
Yes.
I do see some current-production P-E flashlamps rated for 1,000 Hz, so some kind of retrofit seems possible, although one may also need to either replace or augment the trigger transformer.
Joe Gwinn
Reply to
Joseph Gwinn
Thanks. Who is the maker? Do they have application notes and more complete datasheets?
Joe Gwinn
Reply to
Joseph Gwinn
I would have thought dance-floor strobes would be far slower and far more powerful than a Strobotac.
One use of the FX-6A that I've found is automotive wheel balancers that were made by Balance Technology Inc (BTI) and competitors. Wonder what they use these days; I'm sure that won't stand still for $230 per tube.
Joe Gwinn
Reply to
Joseph Gwinn
Hi Joe, what you see is what you get - the data sheet was all that was on a local retailers website. probably, asuming your in the US, that Digikey or Mouser would have similar ones - perhaps they would have more data. The max strobe rate - no idea, but I cant imagine that the listed tube in the original post is the ONLY one suitable in the world.
Its a basis for experimentation - might work, might not, Relatively cheap and easy to lash up - if it works, a nice bit of test gear back on the road, if it doesnt - well, youve blown 10 bucks and a bit of time..... Trigger transformers are also available, about 2 dollars.
I am a working technicain, not an engineer - cant give you voluminous theory on the application, I use the "suck it and see" approach........sometimes works, sometimes a spectacular failure. But I do get enough oddball electronic things like this working to make a (precarious) living.......the high value or rare device thats worth putting a few hours of experimentation into before they go to the dumpster....
Andrew VK3BFA.
Reply to
Andrew VK3BFA
Anyone try uaing one of the new super bright white LEDs for a strobe?
Reply to
Tm
According to Andrew VK3BFA :
[ ... ]
There is also the FX-7 -- which appears to have a larger envelope size, but otherwise be similar, so it might work, except for not fitting the reflector. And I'll bet that it is at least as expensive as the FX-6A.
Yes -- but these are quite unlike the FX-6A.
The FX-6A is in a stubby 9-pin miniature tube base.
It has the two main electrodes allocated to two of those pins.
It has *five* *internal* trigger electrodes connected to five of the remaining pins -- fine wires reaching in to points along the arc path, and all electrically independent.
The Strobotac has a 7-conductor ribbon cable going from the electronics box to the pivoted stem which contains the 9-pin socket for the flash tube, and over which the neck of the reflector fits. (This rather limits the maximum dimensions of the tube to ones no larger in some dimension than the diameter of a 9-pin miniature tube.
The reflector is designed so the arc length (about 1/2" long) is in the focus of the reflector.
The internal flash triggers operate (presumably) at a much lower voltage than external triggers.
The fact that a separate wire is brought out to each suggests that each has a unique voltage applied to direct the arc along the intended path.
Including possibly an induced failure to the trigger circuits in the StroboTac in this case.
While I have the four remaining unused lamps, plus the one in pretty good condition, and one rather darkened from use, I intend to use it as it was designed.
If those ever are all expended -- *then* I will try retrofitting some newer flashlamp. But I think that not too many of those are designed to survive 27K flashes/minute. :-) And I'm not sure about the trigger transformer, either.
O.K. You finally got my interest piqued sufficiently, so I just pulled it out of its case:
1) It is old enough to be tube driven, not solid state. A 5965 and a 5727. This suggests that the trigger circuit is not as fragile as I at first feared.
2) Looking at the ribbon cable end inside the box, the flashlamp main terminals are the end-most ribbon cable leads, the only trigger connection is for the center one, feeding the centermost trigger electrode which suggests that the ribbon cable acts as a capacitive voltage divider to couple signal to the remaining trigger electrodes.
3) The trigger transformer is a potted brick, about 1-1/2 x 2-1/4 x 3/4"
4) The main capacitor for the highest flash level is 1.15 uF at 1000 VDC. The smallest is 0.47 uF, also at 1000 VDC. The middle one is 0.22 uF, again at 1000 VDC. They are all marked "Vicofilm Capacitor" from "Industrial Condenser Company".
5) It does have *some* solid state devices -- a bridge of top-hat rectifiers. :-)
6) There is also a three-section electrolytic. 50 uF, 25 uF, and 25 uF at 450VDC.
7) The speed pot is one of General Radio's special precision wirewound pots, though there are four Allen-Bradley sealed pots scattered around the rest of the circuit.
8) And, of course, it has a custom power transformer, with no useful markings.
9) Two slow-blow (MDL) fuses (1/2 A, 250V) in clips on one of the circuit boards.
10) One NE-2 lamp between two upright braces, secured by a heat-shrink band as a vibration seal. It is presumably a voltage reference, as there is no way for the light to get out, and the pilot light for the speed scales is a bayonet-base incandescent pilot light. (Another NE-2 is used as part of the calibration system -- it is visible through a window in the front panel, and you set the speed pot to specific speeds, and tune the front-accesible pots for lowest brighten/dim rate in the lamp.
11) The date codes on components seem to be in the 1967-1968 range.
Don't expect me to attempt to trace the circuit -- it is General Radio's quality construction of the period, with single-sided circuit boards, but it is too dense a construction for me to bother without serious need.
Understood. But at present, it is cheaper to buy more StroboTacs on eBay than to buy new lamps. So -- as long as the lamps with those are in good shape, you could get one, sell the lamp back on eBay, and experiment with your own StroboTac.
FWIW -- the energy per flash is in three ranges, corresponding to three flash rate ranges, so you don't overheat the lamp and burn it out too rapidly.
Enjoy, DoN.
Reply to
DoN. Nichols
According to Joseph Gwinn :
A good question. I wonder whether they have re-boxed them if selling NOS -- or whether the boxes still say EG&G? :-)
That is possible.
O.K. My examination of the device shows that only one is actually driven directly -- but the others appear to be capacitively coupled through the ribbon cable. I haven't pulled the lamp socket out, but based on the layout of the ribbon cable, I would expect the "sparker" to be the middle of the set.
O.K. Good for slow rotating devices -- but not the top end.
Hmm ... the three main flash capacitors in the StroboTac are all rated at 1000 VDC -- and selected by the range switch.
It is pretty densely packed. The trigger transformer seems to be in a potted brick -- and I *think* that the capacitor is included in that brick.
Not I. One of the things that I looked for while I had it open was a circuit diagram pasted inside the case. No such luck.
O.K. A google Search lead me to a PDF file of a manual for the 1538-A Strobotac -- as slightly later version.
This says that the tube operates at 800-1000 VDC, and the trigger is 5000 V.
O.K. I've found some schematics -- and this one is solid-state, while the previous one (which I have) is tube based -- as shown by another posting this evening on this newsgroup -- so I won't duplicate it here.
Go to

and you will find manuals for both the 1538-A and the 1531-A/B, among others.
I've just bookmarked that -- and gotten manuals for several things which I have.
[ ... ]
O.K. Good luck with those.
Enjoy, DoN.
Reply to
DoN. Nichols
Don, fairly obviously, if you have spares there is no point in trying to fit a substitute. QED. I wonder what the modern equivalent is - probably hand held, LCD readout, and runs forever on 2 by AA cells......a white LED?
BTW - this old gear is interesting from a "antique electronics" viewpoint - I have a shed full of NIXIE based test equip. I will oneday get some of it working, - no point except getting it going.. and if I dont, the kids can curse me as they cart it off to the dump when I die.. ( a 5 digit nixie tube based precision voltmeter is not much use for anything except as a prop in sci-fi movies - see "The Dish" movie if it made it your way, a whole rack full of HP counters on self test...)
Andrew VK3BFA.
Reply to
Andrew VK3BFA
Here is something useful
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Regards,
Boris Mohar
Got Knock? - see: Viatrack Printed Circuit Designs (among other things)
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void _-void-_ in the obvious place
Reply to
Boris Mohar
Somehow I doubt you could get a short enough flash to be practical and I wonder about the max rep rate. Intrested in the results if any one ever tries it. ...lew...
Reply to
Lew Hartswick
The circuit drawings seem to say that all are driven by a 5 KV pulse through 22 picofarad capacitors, one per line.
It may be 800 volts. It seems to depend on the model. It's easy to achieve 600 volts with a voltage quadrupler, without a HV transformer.
It is, according to the circuit diagrams.
Bingo! Of course. I got them. Thanks.
I may also have a way to make an ordinary flashtube work far above it's normal flash rate, based on tricks used to get far above 25,000 plashes per minute.
Joe Gwinn
Reply to
Joseph Gwinn
According to Andrew VK3BFA :
At least at present.
I have my doubts about the LED being fast enough. I believe that the white ones are actually a UV LED combined with a white phosphor mix, and the decay time of the phosphor is in question here.
Of course, there are handheld ones which will *read* a contrasting mark on a part of the rotating device, which is probably quite good enough for determining RPM -- though there are advantages to a strobe which allows you to view a machine through its cycle -- including in my case, view a concertina reed vibrating under pressure of airflow.
Hmm ... I don't think that I have any Nixie based ones left (though some Sperry neon 7-segment displays in old Bridgeport DROs might almost qualify), but I can see your 5-digit voltmeter and raise you two, with LED readouts. (Rack mount, too, of course. :-)
Well ... occasionally, I want to read something as accurately as possible.
And even for resistors -- it has 4-wire mode for eliminating measuring the resistance of the leads.
Of course, somewhere around here I have a plug-in resistor marked "0 Ohms, 1%". I would like to know how they can promise that accuracy with *that* particular value -- even if it were a solid block of silver. :-)
Enjoy, DoN.
Reply to
DoN. Nichols
According to Boris Mohar :
Fun reading.
Thanks, DoN.
Reply to
DoN. Nichols

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