On 201611/14/ 12:20 PM, wrote:
Forgive the top posting but WARNING: if a big honking electrolytic capacitor that is more than 60 years old is rattling when shaken, it is absolutely and irredeemingly, irrevocably TOAST. As are its siblings. Reforming is an exercise in futility, and possibly very dangerous, as if by some chance you do actually reform one (or more) for the moment, and it should fail under actual use, all the work previous would be for naught. **POW**.

Agree on the photoflash caps in any case. However, I suspect that the OEM caps are vastly oversize to make up for their rather slow chemistry.

Peter Wieck
Melrose Park, PA

I hear what you are saying Peter, but those caps are industrial grade
caps, not what you would find in a radio. Agreed the shake test will
tell if they are really bad (no rattles!), however attempting to reform
them is not an exercise in futility unless there are obvious signs of
venting around the rubber plug on the top of the can.

If you have access to an ESR meter that will give you a pretty good idea
of the capacitors condition. We sell the Bob Parker kit (as do others)
and using that with an ohmmeter to see if the low ESR is an actual short
circuit or not will give you a pretty good idea of the condition of
these electrolytic caps.

These would have been photoflash rated caps originally and they were
common in photographic gear from the 50s and on. My dad's architectural
photography studio had many flash boxes that used racks of those caps,
back in the 50s/60s and 70s.

John :-#)#

PS, I forgive the top-posting (ducking)


On Monday, November 14, 2016 at 2:57:48 PM UTC-5, John Robertson wrote:
On 201611/14/ 11:12 AM, wrote:
First, where are you? All the tubes you mention are quite common and not very expensive. I probably have all of them in my rather random connection. The bigger issue are those capacitors.

Please note the interpolations.

On Monday, November 14, 2016 at 1:34:55 PM UTC-5, wrote:
All,
I know almost nothing about tubes(AKA valves). My son bought a
capacitor discharge spotwelder that uses tubes. It doesn't work. Parts
of it do but on the whole it appears that it doesn't charge the caps.
There are three types of tubes in the thing.
3 each OA2WA voltage regulators
2 each 2D21 thyratrons
1 each 5U4GB rectifier
There are also 6 each physically large electrolytic caps that are,
I believe, rated for 450 volts. They are made by Sprague and are
marked 200-450. No uf markings though. Apparently a couple rattle when
shaken-probably not a good sign.

200uF @ 450V. You could pay anywhere from $15 to $100 for those caps. Given the application, do not cheap out, but get as high a quality as you can afford. You also have the choice to put caps in parallel to make the capacity - and series/parallel to make a higher working voltage. There is plenty of room given the size of modern caps to go this route.


There are two transformers. The first has many taps and the second
is connected through a relay to the bank of caps. The secondary of
this xmfr is the spotwelder output.
As near as I can tell the circuit basically operates like so: The
first xmfr provides 450 volts AC which goes through the 5U4GB tube to
be rectified and then through three OA2WA tubes which are connected
in series. From there the power goes to the cap bank and charges the
caps. And from the caps through a big relay to the output xmfr.
The OA2WA tubes have only two of the pins connected. So power goes
in one pin and then out the other to the next OA2WA tube and so on. It
looks like there is no output from the last tube in the series. So
maybe this is why the caps won't charge.


I suggest you consider PHOTOFLASH rated caps - they have a very fast
discharge (low internal ESR - you might want to get a Blue ESR meter to
test these caps) and aren't too expensive...

http://ca.mouser.com/Passive-Compone...oflash&FS=True

Look up REFORMING capacitors. Even old ones like yours may be saved,
there was a recent thesis published that showed how large value caps can
last a long time if they are reformed carefully.

2D21's are very old design - there are many circuits online to replace
them with SCRs if you want to bring the machine up to the 21st century...

Likewise your 5U4s, this can be replaced with a solid state bridge (dual
diode) rectifier. As the 5U4 has its own transformer then you need to
make sure it is fused correctly on the primary side in case of a shorted
diode.

OA2 tubes are 150VDC regulators, so with three of them the output is
regulated to 450VDC. If the OA2s are glowing purple then they are at
their regulated voltage (more or less) - all three need to be glowing
for your 450VDC to be regulated. I would expect them to be across the
output of the 5U4 to ground to regulate the output voltage...

John :-#)#


It is probably a blessing that your rectifier (5U4) tube does not work. Were you to be passing B+ - well, the results may be unhappy - see below.

At least one 2D21 thyratron seems to work because the relay that
connects the cap bank works when the machine is triggered.
I would like to know how to test the tubes without a tube tester.

Other than for filament continuity and gross shorts (shorts on a cold tube), no you have no certain way to test tubes without a tester.

Maybe this means I will need to make a tester. I also would like to
know how to test the big caps. My meter has a cap test function but it
doesn't seem to work with these big caps. Maybe this is because the
caps are high voltage types. Is it (fairly) safe to attempt charging
the caps with line voltage (120 volts) by first rectifying and then
passing the current through a resistor and then to the caps?
Here is a link to pics my son took of the guts of the spotwelder:
https://goo.gl/photos/LF4JKeGyA4YWiCwv9
Any comments about the spotwelder would be much appreciated.
Thanks,
Eric

The big caps are toast - full stop. DO NOT EVEN TRY to operate the tester without them as it is possible to do permanent damage to the transformers if the caps are shorted.

If you are anywhere near the Melrose Park section of Cheltenham Township (Philadelphia area) let me know. Despite the size and industrial application, this is a fairly basic issue to troubleshoot.

Now, showing my age, I used one of those ancient beasts some 40 years ago when I was working as a machinist. When set up properly, they are amazingly versatile. I used one to weld various thickness of inconel wave washers and pimple washers onto stainless steel seal backs for aircraft and nuclear applications. From stuff that was almost as thin as paper (0.004 thick) to stuff as thick as index card stock - dial in the machine, pass the pull-tests and it would hold the setting, effectively, until changed. There was a small stash of tubes above the machine - but no 2D21s. When one of them died one way, I found it at Leon Fertik's establishment for $1.50. I replaced them both and purchased two spares. The machine shop is still with us and thriving. Leon, sadly gave up his shop after his wife passed.

Best of luck with it - I can think of a lot of uses.... Especially if your son is an artist.

Peter Wieck
Melrose Park, PA



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(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."