Tubes in broken spotwelder & other questions

First, where are you? All the tubes you mention are quite common and not ve ry expensive. I probably have all of them in my rather random connection. T he bigger issue are those capacitors.

Please note the > All,

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

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.

The big caps are toast - full stop. DO NOT EVEN TRY to operate the tester w ithout 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 (P hiladelphia 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 w hen 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 ap plications. From stuff that was almost as thin as paper (0.004 thick) to st uff 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 sma ll stash of tubes above the machine - but no 2D21s. When one of them died o ne way, I found it at Leon Fertik's establishment for $1.50. I replaced the m both and purchased two spares. The machine shop is still with us and thri ving. 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

I'm north of Seattle on Whidbey Island so a visit would be unlikely. My son has tried to power the thing up and even though parts do work it won't do any welding. There is no odor of magic smoke so I think the xmfrs are both OK. I told my son not to power it up any more until we figure out what's wrong with the thing. The welder has two ranges:

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...

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.

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 :-#)#

Yeah - that is a bit distant, for now. I did get a chance to visit one of t he participants herein in his native habitat (central Texas) recently, so, stranger things have happened.

At this point:

a) Focus on the caps. Get them replaced with caps rated, either singly or i n combination at 200uF @ 450V minimum. Some basic rules of thumb: Caps in s eries are additive for capacity, but not for voltage. 10 x 20uF @ 450V (IN PARALLEL) = 200uF @ 450V.

Two caps in series must be calculated, but keeping it very simple, if two 2

b) Test the tubes by checking the filaments and for any dead shorts interna lly when cold. A base diagram will tell you which are the filament pins, an d then any pin to any pin not internally connected (also given on the base diagram) for shorts.

There are lots of sources for tubes - if you get stuck, let me know and I w ill root through my spares box. I have 0A2s and 5U4s, most likely in some q uantity. As to 2D21s I am not sure, but they are stocked at Antique Electro nics Supply (AES) for $5 or so.

Then, your best friend is cleaning anything that can be cleaned without dam age. Dust removal, correct lubrication if applicable, rust removal (Beware of steel wool!) and similar.

Best of luck with it - given that you are in the PNW, and, worse, on an isl and, make sure that you keep the system dry and free of salt. Given the ope rating parameters of that beast - you DO NOT want stray currents floating a round.

Peter Wieck Melrose Park, PA

Forgive the top posting but WARNING: if a big honking electrolytic capacito r 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 c aps are vastly oversize to make up for their rather slow chemistry.

Peter Wieck Melrose Park, PA

t very expensive. I probably have all of them in my rather random connectio n. The bigger issue are those capacitors.

te:

iven the application, do not cheap out, but get as high a quality as you ca n afford. You also have the choice to put caps in parallel to make the capa city - and series/parallel to make a higher working voltage. There is plent y of room given the size of modern caps to go this route.

toflash&FS=True

Were you to be passing B+ - well, the results may be unhappy - see below.

ube), no you have no certain way to test tubes without a tester.

er without them as it is possible to do permanent damage to the transformer s if the caps are shorted.

p (Philadelphia area) let me know. Despite the size and industrial applicat ion, this is a fairly basic issue to troubleshoot.

go when I was working as a machinist. When set up properly, they are amazin gly versatile. I used one to weld various thickness of inconel wave washers and pimple washers onto stainless steel seal backs for aircraft and nuclea r applications. From stuff that was almost as thin as paper (0.004 thick) t o stuff as thick as index card stock - dial in the machine, pass the pull-t ests 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 di ed 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.

our son is an artist.

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)

citor that is more than 60 years old is rattling when shaken, it is absolut ely 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 un der actual use, all the work previous would be for naught. **POW**.

EM caps are vastly oversize to make up for their rather slow chemistry.

I keep "that" ESR meter, and it is extremely useful. I also have a neat lit tle cap tester that actually tests caps at full operating voltage (up to 45

-)>

My point is that a capacitor, even half-a-dozen capacitors are usually pret ty cheap if measured against the alternative failing at a critical moment. These are not the typical cap found in the typical radio - there is a LOT o f energy stuffed inside those beasts. Too many for me to trust a 50+ year o ld cage for containment.

Peter Wieck Melrose Park, PA

That's not what I "heard". It should be 10 uF.

(C1 x C2) / (C1 + C2) = Working Capacitance is the equation I have used these many years.

Example 1:

Example 2 (from the link):

At least where I come from.

Peter Wieck Melrose Park, PA

If equal value capacitors are in series (same for resistors in parallel) all you have to do is devide the value of one of them by the number. That would be 20 devided by 2 for 10.

You can also take the long hard way and do the product over the sum as in your example. You just need to LOOK AT THE VALUE IN THE EXAMPLE AS BEING 20 INSTEAD OF THE 10 FOR EACH ONE THAT YOU USED.

For equal values of capacitance the voltage will add, if the voltages are not equal then there are problems. Resistors are needed across the capacitors when equal values of capacitors are used. This is mainly due to the wide variation of capacitance in most of them. Helps to bleed off the stored charge also.

te:

if two 20uF @ 450V are connected in series, the >actual capacitance will b e 5uF @ 900V. "

ed these many years.

OK - I have enough stray caps at home to do a lash-up and I have enough ver y accurate meters to test the actual results of that lash-up. But, I just r ebuilt the power-supply of my Dynaco ST-70 and my actual working results we re as the equation implied, as I remember.

Nor would I ever run caps of differing voltage in series. Or parallel for t hat matter.

I will report my results.

Again, here is the link. I am NOT making this up.

Peter Wieck Melrose Park, PA

Read Ralphs post again?

Example 1:

C1 = 20, C2 = 20

not 10 ...

The previous poster was simply pointing out that you made an error in your math. You had a 10uf and a 20uf cap as your math components based on the link, but were speaking of two 20uf caps in series in the preceding text.

For two identical value caps in series divide be two for the resulting capacitance. Voltage is added. If there are differences in the capacitance between the two caps then the formula is needed.

Hey, we all make mistakes, even I've made one or two (a minute)...

John ;-#)#

I found 220 mfd 450 caps at JustRadio.com. I'm not sure if these will discharge fast enough. I emailed the site and am waiting for an answer. A quick search for photoflash caps turns up 300 volt caps, no

The 220 mfd will work fine where the 200 mfd caps are used. Many of them have a large tolerance of 20 to 50 %or more.

Did you look at the Mouser link I included a few posts ago? They list

Here is a surplus place with photoflash caps, not cheap, but they are in stock:

However, if you use the part number you will probably find a stocking distributor...

JustRadio sells good caps, but they aren't photoflash rated - pretty safe bet on that!

John :-#)#

Might be helpful to take a peek below the obvious.

Take a close look at the pix of the capacitors at the mouser link. Compare the solder pins to the size of the buss bars in the welder. At least you'll be able to say you thought about the consequences of tiny pins and dubious solder connections. That compounds if you go with fewer larger caps. All that energy into the weld came from the caps. It's just as easy to melt the solder at that end.

Don't go too crazy with the cap values. My spot welder is calibrated to deliver energy based on the voltage and cap value. If the cap is different, the calibration can be off by that ratio. If your meter has a square-law scale, that can make a significant difference in calibration at one end or the other. You can't just add a resistor to fix it. But you can put a post-it note on the panel and do the scale factor in your head.

If you don't have a schematic, create one. It only takes one wrong assumption to make a lot of smoke.

Beware saturation in the output transformer. Mine has a core reset pulse between firings. If that part of your system is broke, you can saturate the core. At best, that can take your diagnostics down the wrong path. At worst, more smoke that takes out the parts you just fixed.

Are we having fun yet?

For a welding purpose, 100l milliseconds is very fast (no functioning capacitor you are likely to find would have too high ESR for this job).

ESR gets to be important with low voltage high current, where a fraction of a volt of ripple is a malfunction. Fraction of a volt difference on a 450V capacitor charge is negligible.

I agree that the speed doesn't matter, but low ESR caps have wiring that will survive higher currents. No sense having a whopping cap with internally-fused connections.

I also have a bench-top spot welder, from my father who was an orthodontist. It has a 110V input (so we needed a transformer from 240V), and that feeds via a small Variac into a selenium rectifier. I suspect the caps need replacing (again - they were last done 25 years ago) and I have a bunch of 300V photoflash caps from disposable cameras that I hope will suffice.

The welding contacts are an anvil and an upper contact connected to the foot pedal, via an adjustable pressure-operated switch that fires the contacter. That leaves both hands free to hold and position the work. When you press down hard enough, the thing fires, very cute.

What I don't know is how to determine the maximum energy I can dump through the output transformer without saturating it. Anyone know how I can tell (other than just keeping the capacitance below the original value)?

Clifford Heath.