Re: FX-6A flashtube availability and data

According to Joseph Gwinn <JoeGwinn@xxxxxxxxxxx>:
In article <e21os90t4d@xxxxxxxxxxxxxxxxx>,
dnichols@xxxxxxxxxxx (DoN. Nichols) wrote:

[ ... ]

They were made May 22 1975 according to the stamp on the box
endflap.

I wonder if P-E is actually making the tubes these days, or selling new
old stock one tube at a time.

A good question. I wonder whether they have re-boxed them if
selling NOS -- or whether the boxes still say EG&G? :-)

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.

That is possible.

They also sent me a FX-6A data*** (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).

O.K. Which probably determines the choice of max RPM on the
Strobotac.

Yes.


Arc length is 7.9 mm. The trigger electrode (called the "sparker" is
near to the anode and cathode, inside the glass envelope.

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.

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)

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.

But this suggests that they fire at much lower voltages than the
typical trigger wrapped around the outside of the typical flashlamp.

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.

O.K. Good for slow rotating devices -- but not the top end.

The required voltage and energy was not documented.

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.

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.

Hmm ... the three main flash capacitors in the StroboTac are all
rated at 1000 VDC -- and selected by the range switch.

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.

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.

Does anyone have a circuit diagram?

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

<http://www.ietlabs.com/pdf/Manuals/>

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.

[ ... ]

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.

O.K. Good luck with those.

Enjoy,
DoN.

--
Email: <dnichols@xxxxxxxxxxx> | Voice (all times): (703) 938-4564
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