'66 EE drive problems update

Hello, all,

This is the continuing story of my EE drive, as of today.

As was mentioned earlier, Angelo, the electrical engineer, found that I had the taps on the transformers in the wrong position, so the filament voltage was slightly out of spec. He reset the taps, and got the voltage set within the 2.5V +- 5pct. tolerance. We left the machine at that point, as Angelo said he'd have to make up a 'high voltage probe' system for his oscilloscope, to set the phasing of the tubes.

The out-of-tolerance voltage seemed a plausible cause for the failure of one of the tubes.

Yesterday, I installed the three new tubes.

Today, Angelo checked out the phasing of the C16J tubes, and, as chance would have it, I had hooked them up 'right way round', so to speak. The phasing checked out OK.

After letting the new tubes 'season' with power on their filaments for an hour, without drawing power from them by running the spindle motor (I'd been told that they needed time to do an initial vapourisation of the mercury in the tubes before they were capable of actual use), we started the machine.

The spindle motor ran smoothly, and seemed to brake alright when the switch was thrown off.

However, now the machine has a new problem.

The motor speed follows the speed control knob only up to less than half of the speed control travel. It runs smoothly and quietly up to 950 rpm, as indicated on the tach, but won't continue to increase speed past that point. The motor continues to run smoothly at 950 spindle rpm, regardless of control pot knob setting past that point, roughly a third of the control knob's range of rotation.

Previously, up until the fallure of the one C16J, the spindle speed would run up to 3500, approx. , at the max speed control setting, and seemed to follow the control knob setting normally up through its range, altho the motor would seem to 'hunt' a bit at around 3000 spindle speed.

Aside from going over large numbers of wiring terminal screws with a screw driver, to verify that none were loose, and replacing the tubes, nothing has been done to the machine's electricals.

Is this new problem, the failure to run past 950 rpm spindle speed, a known problem, with a known diagnosis/repair?

I did notice that the new C3J tube looked visually different in operation, compared to the old existing one. The old one showed a strong light blue glow, whereas the new one seemed to glow much more weakly, with what appeared to be 'red flickers' in its glow.

Could a new but defective C3J tube cause such a problem?

I haven't yet tried running the machine with the module removed, or substituting the old C3J.

Is there anything I should look for, such as some of the diode parts in the module having failed, maybe just from age?

cheers

Carla

carla @ tactical link said:

Could a new but defective C3J tube cause such a problem?

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Yes, and it's the most likely cause. Replace it with the one that was working and see if that fixes things.

BTW: A C16J is xenon filled and has no mercury.

Without any sort of quantitative information about their intensity, my guess is that the red cast is not a problem. The difference in glow indicates a difference between the thyratrons, but if it is not too great, it also is not something to worry about. The tubes are firing on alternating half cycles, so an unbalance will show up on an oscilloscope. Thyratrons are fitful beasts that vary from one to another and age differently. They have been replaced by solid state components almost everywhere and except for the light show, I don't miss them a bit.

I agree that you have a field weakening problem.

Bill

rke[pler said:

Yes, and it's the most likely cause. Replace it with the one that was working and see if that fixes things.

BTW: A C16J is xenon filled and has no mercury.

Click to expand...

Thank you, Mr Kepler, that was the problem.

The little EE now runs smoothly up to 3500 (it might have gone to 4000, for all I know, but 3500 is more than fast enough for me)

Just as a point of curiosity.........I was told by one of the parts/service dept. people at the Monarch plant, back in the days before the internet, when I'd called for advice on mending another Monarch lathe, that should I replace any C16J tubes with new ones, it was imperative that the tubes be allowed to stand with the power to the filaments 'on' but without drawing power to run the spindle motor, for at least half an hour's time, preferably an hour or more.

I thought I remembered being told that this was to allow the tube to warm enough to vapourise some material in the tube which formed a 'coating' or 'deposition' on internal components of the tube.

Had I remembered this correctly, and, if so, what would have been the reason for this 'initial break-in' time?

cheers

Carla

carla @ tactical link said:

The little EE now runs smoothly up to 3500 (it might have gone to 4000, for all I know, but 3500 is more than fast enough for me)

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Lots of chucks aren't happy at 4K, so unless you're running the bare spindle you're likely better off keeping the speed down. I don't think I've ever spent much time at 4K myself, I keep thinking about all the energy in the motor spindle, lathe spindle, sheaves and wonder where it'd all go in an emergency.

Just as a point of curiosity.........I was told by one of the parts/service dept. people at the Monarch plant, back in the days before the internet, when I'd called for advice on mending another Monarch lathe, that should I replace any C16J tubes with new ones, it was imperative that the tubes be allowed to stand with the power to the filaments 'on' but without drawing power to run the spindle motor, for at least half an hour's time, preferably an hour or more.

I thought I remembered being told that this was to allow the tube to warm enough to vapourise some material in the tube which formed a 'coating' or 'deposition' on internal components of the tube.

Had I remembered this correctly, and, if so, what would have been the reason for this 'initial break-in' time?

Click to expand...

Well, it's true to some extent for all tubes and a lot more for a mercury rectifier such as the EL1C and 3C23 thyratrons in the WiaD drive (the mercury based tubes really do need 15+ minutes on time before first driving them). A tube will be damaged if you drive them cold, that's why there's a timer on the start circuit to keep you from running for a minute after starting (and giving it a little more time from *really* cold isn't a bad idea). But none of the thyratrons in your drive are going to have their lives shortened a lot by running the drive a couple of minutes after a cold start.

rke[pler said:

Lots of chucks aren't happy at 4K, so unless you're running the bare spindle you're likely better off keeping the speed down. I don't think I've ever spent much time at 4K myself, I keep thinking about all the energy in the motor spindle, lathe spindle, sheaves and wonder where it'd all go in an emergency.

Concur..........I'd removed the collet drawbar assembly, and had only the collet nose on the spindle when it spun it up briefly, just to see whether it would run up to speed. The original 4-jaw chuck would probably suffer 'rapid kinetic disassembly', much like a grenade, at 4000. (actually being a civilian pacifist, I've never gotten to experience grenades, first-hand......but I've spalled rocks down with 1/4 sticks of powder, 'mud-capping' them, and thats well and truly 'dramatic' enough for me)

If I remember correctly, Tom, of 'Tom's Wheels' said that he re-speeded his EE down by 2o% with a larger spindle pulley, and I mean to do likewise. Thats 3200-ish max, which is still too fast for many chucks. I use HS tools, particularly form-tools, probably more than most, and just don't use high spindle speeds.

Well, it's true to some extent for all tubes and a lot more for a mercury rectifier such as the EL1C and 3C23 thyratrons in the WiaD drive (the mercury based tubes really do need 15+ minutes on time before first driving them). A tube will be damaged if you drive them cold, that's why there's a timer on the start circuit to keep you from running for a minute after starting (and giving it a little more time from *really* cold isn't a bad idea). But none of the thyratrons in your drive are going to have their lives shortened a lot by running the drive a couple of minutes after a cold start.

Click to expand...

Alright......it was a 'works in a drawer' Monarch EE about which I'd called the Monarch works for advice.....so the advice about the tubes was needed for that unit.

On this later EE, I've always let the tubes warm for ten or fifteen minutes before starting the spindle, if the machine hasn't been run for some time.........just to be careful with them.

cheers

Carla

carla @ tactical link said:

...
On this later EE, I've always let the tubes warm for ten or fifteen minutes before starting the spindle...

Click to expand...

Can't hurt, but the data sheet for the C3JA and C16J is pretty clear in stating a 60 second warm-up time is all that's needed before pulling load current. The time delay relay in your modular EE takes care of this for you by not allowing the HV to be turned on until 60s after power is applied...

You are correct that the long warmup for mercury vapor tubes is to boil any liquid mercury off the filament and out of anywhere that can cause a flashover. If they have been standing upright stationary all the time, it is not so important. The problem is with tubes that have been shaken or bumped on their sides, moving the mercury drops to where they can do damage. When installing a new tube, there will often be mercury all over the glass. After the initial bake, there will be a clear band around the elements where the mercury has boiled away.

The filaments for such tubes require special qualities because the large currents being controlled mean emitting a lot of electrons and carrying anode currents that are a significant fraction of the filament supply current, which is added to lighting them up. They have to be large enough to start the process and then be able to withstand the additional current. They often have coatings to improve electron emission. I read somewhere a long time ago that applying the high voltage prematurely can pull the coating off. It didn't explain why.

BTW, I have an RF heater that has Phillips 872 rectifiers that are gas filled, possibly xenon, and no mercury. Phillips, sold in the US as Amperex, seemed to be determined to not do anything the way American manufacturers did it. They work well.

Bill