Drug Store Tube Tester
If you're old enough you might remember seeing one of these in a drug store, grocery store or even Radio Shack. You could pull all the tubes from your radio or TV, put the in a paper bag, and take them down to your local store to test them. And hopefully you wrote down which one came out of which socket. Once you found the bad tube, or tubes, the store proprietor would unlock the bottom and find new tubes. And the price list is taped right inside the door.
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This tester did not have a manufacturer's label anywhere that I could find, so at first I wasn't sure what company made it. It says Sylvania on the plastic face and inside the meter, but the meter label is just a cut out, paste on label, and the plastic face just slips in a slot and could be changed to anything you want in a matter of seconds. However, I recently stumbled across one of these testers that is identical to mine except for the Sylvania labels. It turns out that this is a U-Test-M brand and someone put a Sylvania sticker right over the U-Test-M name in the meter.
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All the electronics are on the tube socket plate, so the rest of the cabinet top is pretty empty except for the AC wiring and flourescent light. And the tube chart.
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The lower section contains the tube drawers and price list.
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The back of the tube socket plate. The's a power transformer, a lot of wiring to the sockets, some range and current limiting resistors, and a small PCB.
I found two 100Ω 2-watt power resistors out of tolerance and replaced them. All the resistors on the selector switches are still OK. The connector plugs for the tube socket wiring had some corrosion, as did the switch contacts, so they were all cleaned with contact cleaner and Deoxit. |
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The PCB has three transistors, and on the backside are half-a-dozen trim pots. No labels or instructions anywhere on what the trimmers do. The only component replaced on this board was the electrolytic capacitor.
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This is an emission type of tester but it actually does a pretty good job. If a tube reads good and has no shorts I usually go with it. If a tube reads bad or shorted I won't toss it without pulling out one of my other testers, like the TV-3 or Precision 10-12, to double check it. But the drugstore tester is usually right. The only time I've ever had an issue was with power tubes, which I think was caused by corroded pins on the interconnect cables, and was fixed when I restored it. Now it works great and I find it quite handy to have sitting there ready to go at the flip of a switch. And it just looks cool.
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Page created 3/29/2021
Last edited 4/10/2021
Last edited 4/10/2021
