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Testing the viability of thyratrons

TDegenhart

Diamond
Joined
Mar 26, 2011
Location
Geneva Illinois USA
There seems to be a lot of problems lately about whether a thyratron is functioning correctly. Some of the more resent posts.

http://www.practicalmachinist.com/vb/monarch-lathes/1956-wiad-drive-problems-284150/

http://www.practicalmachinist.com/vb/monarch-lathes/tube-failure-questions-290034/

http://www.practicalmachinist.com/vb/monarch-lathes/grid-voltage-assymetry-292471/

http://www.practicalmachinist.com/v...dular-c16j-grid-transformer-work-wiad-293039/

I feel reasonably sure that with a little digging I could find a lot more more like these.

My question is, can thyratrons be tested by disconnecting the grid connections from the tube and substituting a Variac or equal between the cathode and the grid (through an isolation transformer of course)? The tubes are quite expensive and there is no longer the corner drug store that one can take the tubes to for test (not that one originally could!).

We have available people that are either experts on this subject or very knowledgeable that have chimed in but I sense a lot of frustration by owners. Is it possible for someone with the right equipment, transformers, scopes, etc, that could rig a test setup where a tube could be shipped for testing? I would do it, but all I have is the scope and voltmeters. I have no working knowledge of thyratrons.

Does Monarch have test manuals for these machines that outline in detail how each circuit works and how to trouble shoot it?

Tom
 
In-circuit tests to answer that have been covered several times.

What could a bespoke test rig bring to the table?

It would need a realistic dummy load and a means of measuring control grid effectiveness.

The first is not at all easy, let alone portable when the load is a meant to be heavy and powerful motor, not a lightweight resistive heater.

The second is useless information if it happens to remain effective, but only if operated outside of the range a 10EE (or wotever) can actually provide and still balance one tube with its mate(s).

And then.. IF such a rig existed, a person holding tubes, no lathe, would have to ship them off to be tested - perhaps for a fee as well as r/t transport. THEN ship - hopefully only GOOD ones - again. To the customer. They are easily damaged.

Where's the gain over shipping them directly to the (potential) customer and pricing in either risk, warranty, or some compromise reasonable to what has become, after all, a VERY tiny market?

???

NB: It is WISE to JF replace any and ALL the resistors, capacitors, and diodes. New ones just do not cost enough to justify testing old ones, let alone trying to get another half century of use out of them. Ditto wire and end-terminations.

A test setup to vet the health of the transformers would then be much easier to implement than one to test the tubes.

Tubes then become last suspect standing.


Bill

Not really that hard. Hook 240 V single phase between the anode and filament - terminal through a resistor that draws something near half the full load current of the motor. Inductive or resistive doesn't matter. Connect a DC supply between the grid and filament -. Start with the grid at around 15 volts negative and swing it toward positive until the tube fires. An analog voltmeter across the load resistor will give enough information about the firing point. DC on the grid tells more than a pulse because it shows the anode firing voltage for a given grid voltage. The filament transformer would be the heaviest component. The unit would be small enough to ship around.

I could build one from stock, but right now I am in the unusual state of having a backlog of work, mostly due to a 1236 Chevalier surface grinder that was doing odd things. We wound up removing the table and saddle, then rewiring the saddle. We never found the table travel switch wire that was grounding out, but shotgunning it cured it. I just love working on machinery that has to be disassembled with a forklift.

Bill
 
Interesting thread. I might actually try to build this thing, if I can get a filament transformer cheaply. I could get a variable 24 VDC power supply for a reasonable price. Bill, it seems that the resistor would have to be pretty impressive. Basically a braking resistor, am I correct? I was thinking (just estimating) that FLA or the motor would be ~24 amps. So @12 amps - 240VAC, I am calculating I would need a 20 Ohm resistor that could draw 4.8 kW. I am sizing this based on the AC component which I would think would be higher. This is the part that is confusing to me because wouldn't there be both an AC component and a DC component at the resistor?
 
Interesting thread. I might actually try to build this thing, if I can get a filament transformer cheaply. I could get a variable 24 VDC power supply for a reasonable price. Bill, it seems that the resistor would have to be pretty impressive. Basically a braking resistor, am I correct? I was thinking (just estimating) that FLA or the motor would be ~24 amps. So @12 amps - 240VAC, I am calculating I would need a 20 Ohm resistor that could draw 4.8 kW. I am sizing this based on the AC component which I would think would be higher. This is the part that is confusing to me because wouldn't there be both an AC component and a DC component at the resistor?

As mentioned, electric stove elements are in that wattage range. As I recall the elements on my GE cooktop are 2.4 and 4.8 KW, so a combination would get any reasonable load. Don't worry about AC and DC components in the load. It doesn't care. What we are attempting here is not to duplicate the exact operating conditions in the lathe, but rather to establish if the tube is useable. Get a copy of the tube operating characteristics and compare what you get on the bench with that. Further, if you really want to go cheap, use a battery and potentiometer for the grid voltage. A 9 volt should work quite well.

http://frank.pocnet.net/sheets/049/c/C16J.pdf

I can hear it now from Thermite: "Now wait a minute....!"

Tom
 
I have a good supply of locomotive cab heaters. These are U shaped with fins and mounting flanges, a little over a foot long as I recall. They are rated at about 1700 watts at 72 volts, so 3 or 4 in series should do it. You would want a DC analog meter for averaging reading the voltage developed across the resistor. It would read about 120 VDC if you were getting firing over the entire half cycle. I most likely have meters for this and grid voltage in the collection.

You wouldn't need a fan on the heaters unless you were doing a long test.

The grid voltage would be controlled by a pot, circa 1000 ohms with a 10 K grid resistor. You want to read the grid voltage at the pot wiper rather than the grid because the grid will change voltage from the discharge. Any little 12 V transformer with a full wave bridge will do for a supply.

Bill
 
I have two C16J tubes that has some plating on the inside of the tube around the upper part? About 70% up from the base to the top. These were given to me many years ago. I could install them and try them out, but want to make check and see if these weird looking C16J tubes could fail something else on the drive. Is this any indication of failure?
 
Monarch can test your tubes for you.
The C16J tubes were used in some light systems to light baseball fields and some TV stations.

Hal
 
If you have a working 10ee that uses C16J tube(s), substitute it with your suspect C16J tube and put your 10ee through its paces.

Now, tell me those of you with electronic smarts, what would you do to put it through its paces? What would indicate success or failure?

Inquiring minds...

John
 








 
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