Saturday, September 19, 2015

Memory Lane: Heathkit TC-2 Tube Checker


The Rose Bowl Antique Flea Market strikes again. While wandering around there this past weekend I ran into a guy that had a booth full of cool old electronics and musical equipment. One thing that caught my eye was a nice little tube checker, a Heathkit TC-2.

In case you are not quite as old as me, Hath was a company that sold electronics kits from 1947 to 1992. This company’s products allowed everyday people to get access to electronic equipment that they would not otherwise be able to afford. The kits provided everything needed to put the equipment together, except for the tools. Most of the products from this time were put together by hand anyway, so by supplying their own labor there were significant advantages to this approach. The kits were well planned out and the instructions were the best around, so if the hobbyist was careful, everything would go as planned. They had kits for most everything, from ham radios to oscilloscopes, and even computers in Heath’s final years.

So, this TC-2 was originally kit that put together by somebody, somewhere. It makes me wonder about its back-story, and I wish I knew a bit more about where it came from.

As far as application, this would be a fine piece of equipment if you just want to check tubes at home, but for serious audiophiles or high-end amplifier repair you are going to want more. You see, this is a simple emission tester, not an mutual conductance checker. That means it can test for shorts and cathode (or filament) emission only. The meter reading gives a good-bad reading for the tube by testing for cathode emission by subjecting it to test as a diode (or rectifier). So, this type of checker will indicate if a tube is usable and how strong is the cathode emission is. Both types will do a good job testing for shorts and leakage. A mutual conductance checker applies voltage to each element of the tube, supplies bias and a signal to the control grid, and subjects the tube to a more authentic test (like it would be in an actual circuit). It can measure plate current and allows the tech to create matched pairs. The TC-2 will not do this…

This tool is pretty easy to use. There is a roller on the control panel that shows common tubes, and includes information about which connections to make, what load to set, and the filament voltage (there is also a supplemental chart tacked to the lid of the box with information for less common tubes). The user sets filament voltage by selecting a secondary tap of the correct voltage, and the vacuum tube is set up as a diode with all grids connected to the plate. Then at a specified voltage and load, the tube should draw a specific current based on cathode emission. This measurement is shown on the meter. Shorts and opens can be tested by disconnecting the grids or by shorting them to ground, respectively.

The TC-2 is better than most of its contemporary counterparts, in that it utilizes all tube elements in the test (most only used two). It can test nearly most consumer tubes from the 1920s to 1960s including big pin, octal, loctal, 7-pin, and 9-pin miniature. Newer model tubes that cam out after the 1960s can only be tested with an adaptor.

This Heathkit TC-2 is complete, and in very good condition. The original Tolex-covered case still has most of its latches, and the selector drum is still in great shape. It does not even smell funky. I imagine the capacitor might be a bit funky after this much time, and I would check and/or replace it if I was going to put it into use.

I ended up buying the tube checker for a few bucks and gave it to a co-worker who loves old stereo equipment, as we had talked before about how cool it would be to have one, but the old ones were just too big to keep around the sop. I wonder if it works…


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