Veeco TG-7 TC gauge schematic and hamfest tale

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Richard Hull
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Veeco TG-7 TC gauge schematic and hamfest tale

Post by Richard Hull »

Well, hamfests are back in style after mean old scary covid is gonzo here in VA to the point of just ignoring it and no masking it.

The Manassas Hamfest was this past Saturday. I picked up the usual assortment of goodies. In blasting thru the "pickens" to be had, I actually passed over what I thought was an old PID controller at first glance. On my third pass through the offerings at a more leisurely pace, I actually looked this item in the face. There be Millitorr on the meter!! It was a filthy thing. Musty, dirty, power cord clipped off to 1-inch stub, cover lose, and about 5 cal tags all dated to as late as 1975 plastered all over the face and body.

With my usual disdain, I asked if the guy had the cables and sensors that went with it. No was his answer. Dose it work? "Sorry buddy, I don't know but I think it will accept J or K thermocouples." How much, I asked? 50 cents, he blurted out. I gave him two quarters and wandered back to the car to dump my back pack and the Veeco.

Once home, I checked and the Veeco used a DV-1 TC tube. However a check of the TC gauge tube data I have on hand indicated both the DV-1 and the DV-6 are identical 10mv tubes with identical pin outs but the DV-1 needs about 40ma on the heater, the DV-6 needs about 20ma.

In testing the device, I found it had a constant voltage ferro-resonant power transformer with a 6.6VAC output winding. (stable voltage warranted).
Otherwise, the circuit, like all TC gauge circuits, was abysmally simple, provided you have the proper meter. The Veeco did have the right meter, of course. I back traced the schematic which I attach here. I have several brand new DV-6M tubes on hand here and no DV-1 so I decided to more than double the 15 ohm 5 watt limiter resistor in the Calibration circuit to 39 ohms at 10watts. (had one on hand). I made up a XLR to octal female cable and plugged in the DV-6M. I replaced the clipped power cord. I then cal'd the meter and had it pull down to 13 millitorr (~10 microns) with my Edwards 12, direct drive test pump.

I let the pump and Veeco run for about 5 minutes and noticed the pressure was rising!! Shutting the pump off and removing the XLR cable, I went back to the bench and felt the transformer and it was rather warm. Touching the largish 1ufd 250vac old style, vertical mount, oil filled transformer capacitor it was hot as hell! I grabbed a large 1 ufd 500V orange drop capacitor and installed it in the circuit after pulling out the old oil cap. I hooked every thing back up and ran for 15 minutes. The cal remained good for the entire run and the orange drop was at ambient, so, it was fixed.

The cleaning was a tedious effort. Blowing the dusty guts with my high pressure air hose removed years of dust bunnies and dead bugs collected over many years due to the well ventilated top cover. A long period of using WD-40 and Goo-gone removed the old unsightly cal tags festooning the case and front panel. Tub and tile cleaner did the cosmetic cleaning. See the images.

When I get orphans like this, I just gotta' fix 'em up.

Richard Hull
Attachments
A clipped tail AC cord and filthy back of the item as purchased
A clipped tail AC cord and filthy back of the item as purchased
A very ugly face as purchased
A very ugly face as purchased
A clean rear is a pretty rear
A clean rear is a pretty rear
A clean face is a pretty face
A clean face is a pretty face
Veeco TG-7.jpg
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Jerry Biehler
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Re: Veeco TG-7 TC gauge schematic and hamfest tale

Post by Jerry Biehler »

I tossed one of these the other month, it just stopped working, no idea why. Checked all the components inside and they measured as it should. I just replaced it with an old Varian 840 and scrapped the old one Veeco.
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Richard Hull
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Re: Veeco TG-7 TC gauge schematic and hamfest tale

Post by Richard Hull »

Once I pulled the old oil cap, I checked its capacitance with a precision Beckman digital and an old Sprague magic eye tester. The Beckman read 1.01 ufd. The the Sprague read very close to 1 ufd. The orange drop fixed it. Must have been some variable ESR issue in the old cap. It sometimes happens that way in electronics. Testers would not lie outright, but may never see issues or diagnose the component in its normal active mode.

Finally some poor folks here in the past, present and future, might kill for a 50 cent TC gauge controller. The retort to that is..."would they know what it was at sight?" "Would they have the savvy to fix it or even wire in the tube?"

Oh well, for what it is worth....

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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