This is an archive based on a page that used to be at It has been reassembled from my copy (saved when the site was live) together with files retrieved from and other resources. Hundreds of other files have been kindly contributed over the years too. Many of the files here are just schematic diagrams but some include additional information such as specifications, and a few are complete manuals. 'Partial manuals' normally include everything apart from construction details. 595 files available. Click a row in the table below to download the file. You may download up to 5 different files in a 30 minute period.

1. Heathkit Tc 2
2. Heathkit Tube Tester

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Just got a TC-2 tube tester in very nice cosmetic condition, looks like it's never even been taken out of the box. However, it isn't working properly. It has the following symptoms: 1) The filament in the tube being tested does not glow.

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2) The needle on the meter moves to the middle only when a tube is inserted in the socket (I've read it should go to the middle upon powering up, before a tube is inserted). 3) The short light seems to be out, I have yet to see it flicker. 4) On a random test with a volt meter, it appears most of the taps out of the transformer are putting out the proper voltage (I checked the lower end of the spectrum, up to the 6.3v tap).

5) Nothing inside looks burned or damaged, but all original caps, resistors, & diodes are obviously old (1958). 6) Pilot lights come on just fine (scroll lamps) 7) When in 'test' position, all tubes drop the meter to zero, even known good tubes. I'm guessing that may be because the filament isn't glowing? 8 ) The line adjustment knob does calibrate the line, but only when a tube is inserted. I have already ordered a replacement diode and the large cap (.1uf 600V), will be replacing those tomorrow. But that's just routine. Any advice would be greatly appreciated.

I've done lots of electronic work, but I'm new to tube testers. Might be important to mention that I've only tried 6L6GC, 5881, and 12AX7 so far on this tester.

All of which are a 6.3v filament. I've been looking for some simple troubleshooting info online, but can't find these symptoms exactly. I'm guessing the problem might be obvious to someone familiar with these tube testers. 1) The filament in the tube being tested does not glow. Very abnormal. May be due to a bad solder joint or open circuit somewhere in the unit. The lever switches need to be properly set up for the tube under test, as one of their functions is to complete the filament circuit.

2) The needle on the meter moves to the middle only when a tube is inserted in the socket (I've read it should go to the middle upon powering up, before a tube is inserted). There's a switch on the right hand side for Adjust Line/Shorts and Tube Test. It has to be set to the Adjust Line position in order for the needle to go mid-scale. The 'Adjust Line' control is then used to bring the needle to the center mark. Note that this should be done with the tube in the socket and the lever switches properly set.

3) The short light seems to be out, I have yet to see it flicker. Lack of flicker doesn't necessarily mean there's a problem, especially if the tube isn't even lit up.

Of course the aforementioned switch needs to be in the 'Adjust Line/Shorts' position first, and you have to flip each of the lever switches in turn. You can test the shorts test by connecting a 1-megohm resistor between the various pins on one of the sockets to mimic a typical tube 'short,' then see if the light turns on when you go through the lever switches. 4) On a random test with a volt meter, it appears most of the taps out of the transformer are putting out the proper voltage (I checked the lower end of the spectrum, up to the 6.3v tap). 5) Nothing inside looks burned or damaged, but all original caps, resistors, & diodes are obviously old (1958).

6) Pilot lights come on just fine (scroll lamps) All good signs of life, but it's still not working. Look for miswiring-always a possibility with kit equipment-or dirty or damaged switch contacts. Open or badly out-of-spec resistors also need to be checked for. 7) When in 'test' position, all tubes drop the meter to zero, even known good tubes. I'm guessing that may be because the filament isn't glowing? It's an emission tester, so no filaments = no emission = no reading. 8 ) The line adjustment knob does calibrate the line, but only when a tube is inserted.

That's probably OK. IIRC, my TC-2 (which I no longer have) did not seem to have any real control of line adjustment until you put it under a little bit of load by plugging a tube in.

I have already ordered a replacement diode and the large cap (.1uf 600V), will be replacing those tomorrow. But that's just routine. Any advice would be greatly appreciated. I've done lots of electronic work, but I'm new to tube testers. The diode may be a meter rectifier, and is used for the line voltage adjustment only. They were often specialized, low forward drop devices.

If you replace this with an ordinary diode, the calibration of the meter is likely to be incorrect on the line voltage adjustment. It seems as though the line voltage adjustment was working OK, from what you said above, so this may not be something you really want to mess with.

The capacitor is used only for the shorts test. While it's probably a good idea to replace it on principle, it's not going to make any difference for most of the symptoms you mention. 'Hell, there are no rules here-we're trying to accomplish something!' Thanks Chris, that's all VERY helpful information. I was testing a few of the resistors: of the 9 or 10 in the circuit, all but two test well within spec, but two are about 20% off. That seems like too much.

I'll replace those two. I read somewhere that someone used an IN4007 diode in place of the old selenium diode, and it worked out. But I have no idea if it messed up their accuracy. I'll avoid that change for now.

All of the contacts seem quite tarnished, I'd better clean those up. I'm hoping the filament switch isn't the issue, that would be difficult to replace. I have a suspicion that the reason this tester might be so clean & unused looking, is that the builder might have built it and never been able to get it to work properly, so he put it away in its box. It seems the original build instructions had an error in that the diode direction was shown backwards. I'll be checking that out. But the old selenium diode does not seem to have a visible arrow on it.

I'll keep poking around. Hope it's nothing major.

Set the tester for a 6SK7 tube. Connect a 1000 ohm 1 watt resistor across your DVM prods, and insert them into pins 2 and 7 of the octal socket. Rotate the filament voltage across all settings and check the voltage are correct at every step.

Okay, did this test and it worked out quite well. Definitely need the 1 watt resistor though.

Even the 1 watt began to heat up alot when I got to the higher registers of filament voltage (85v & 115v). I'd probably use a 3 watt next time. Anyway, all my filament voltages looked about right (they'll be even closer when I change a couple of resistors that are out of spec (about 20%). The tester is beginning to come to life.

I've actually tested a few 12AX7's and a 12AT7. The odd thing is, the 12AX7's all showed good only on one side, bad on the other. I know they aren't all bad that way, so I suspect the tube socket might have one bad pin input (number 5 doesn't look so good. On visual inspection). The 12AT7 tested perfectly however, both sides. My 6L6's still aren't testing good (and they are known good tubes), I'm guessing the octal socket is wired incorrectly.

I also went thru and cleaned some contacts, they are all quite tarnished. That may have helped.

I'm going to get some contact cleaner and give everything a good blast. So far, so good. Last edited by on Jan Thu 26, 2012 9:45 pm, edited 1 time in total. The one thing with kits is the soldering. Many people spent a lot of time and care building their kits but did not know how to solder properly, and worse, did not know the signs of a bad solder connection.

The result was kits that worked poorly if at all. The good news is many of these kits were put aside and forgotten for years.

When they hit the market, in the case of the TC2, more than 50 years later, only simple repairs are needed. All the parts, save electrolytics, have not aged and worn. Tube testers like the TC-2 and the TC2P were worked hard in shops and many will be found with worn out miniature, nine pin and octal sockets.

It is a very good tester, and even if you have no tubes, the transformer is a handy source of AC for a variety of experiments. de VE7ASO VE7ZSO Amateur Radio Literacy Club. May we help you read better. Function is quite sporadic now that I've used the contact cleaner. Here is what I'm getting now: 1) The meter now goes to the middle when the unit is turned on (no tube installed), instructions say that's one indicator of proper function.

That wasn't happening before. So that's a good thing.

2) I have successfully tested 12AX7's (both sides now) and 12AT7 (both sides). Also a good sign. 3) I cannot seem to get the filament to glow at all on a 6L6 (octal socket). However, I ran the test using the 100k 1w resistor on the octal socket and all filament voltages look pretty close to spec (they are actually a touch on the low side).

Since that test is on the #2 & #7 pins in the octal. I guess those pins are ok. 4) I've seen the short light blink once or twice while flipping levers. That's also a good sign (bulb is good). 5) The strangest part is: I can go back and put a 12AX7 or 12AT7 in and it won't test. Then 5 minutes later, it'll work great. But I'm still thinking dirty contacts.

Very sporadic. 6) One thing I have noticed is: when the 12AX7 (or 12AT7) is going to test correctly, the meter needle sits slightly above half (and the filament begins to glow). Whereas if it's sitting perfectly at the halfway point before I hit the test button, I know it won't work (and when I say won't work, I mean it shows the tube as bad). On one occasion, I jiggled one of the toggle switches and got the meter to bump up above half a bit. And then I knew the tube would test properly (filament started to glow also). So I'm thinking most of the issue is probably bad contacts from sitting for so long causing no voltage to the filament.

As soon as I get that filament to glow, the tester works perfectly. I'm also thinking there may be a bad connection to the octal socket, but I've touched up all solder joints and still no luck. Gonna double check all the wiring at this point. All resistors have tested in spec by the way (give or take 5%).

Heathkit Tc 2

Assuming the diode is fine. And I have no idea about that capacitor.

80% of the 3 position toggle switch contact points look black, the clean ones look silver (as in probably silver plated?). Even the contact cleaner isn't doing much in there. Might have to remove each switch and clean the contacts with an eraser. Tedious work.

I cannot seem to get the filament to glow at all on a 6L6 (octal socket). However, I ran the test using the 100k 1w resistor on the octal socket and all filament voltages look pretty close to spec (they are actually a touch on the low side). Since that test is on the #2 & #7 pins in the octal.

Heathkit Tube Tester

I guess those pins are ok. Forget the resistor on tour DVM for now. Measure the voltage at pins 7 and 2 of the big-pin 7 pin socket.

Then plug in a 6L6 and see if the voltage drops. Check the line adjust rheostat for bad spots. The wiring harness for the 2 and 7 pins, starts at the 2 and 7 lever switch and goes around the sockets. The selected filament voltage goes the 2 bus wire running across the switches. Have you the manual yet? This will give you the general idea. One hint: On this tester, the tube sockets are wired so all of the pin 1's are connected together, all of the pin 2's are connected together, all of the pin 3's are connected together.

So if you put a tube in the octal socket, you can monitor the heater voltage at one of the other sockets that has a pin 2 and a pin 7. A tube like a 6L6 draws considerable heater current (0.9 amp). Consequently, any resistance in the switch contacts, tube socket contacts, or cold solder joints is going to keep it from working.

Note that this includes the filament voltage switch as well as the pin 2 and 7 lever switches. Another approach would be to set the tester up to check the 6L6 but do not put the tube in the socket. Then unplug the tester from power and measure the resistance from pin 2 to pin 7. You should be able to measure the resistance of the transformer winding, which will be very low, maybe one Ohm or so. If you get more resistance than that, trace the circuit through the switches until you find where it is coming from.

A resistance of perhaps a few Ohms or more would be enough to keep the tube from lighting up. What are you using to clean the switches? Ordinary contact cleaner from Radio Shack or a home center might not cut it.

You might need something stronger, like De-Ox-It. 'Hell, there are no rules here-we're trying to accomplish something!' A tube like a 6L6 draws considerable heater current (0.9 amp). Consequently, any resistance in the switch contacts, tube socket contacts, or cold solder joints is going to keep it from working. Note that this includes the filament voltage switch as well as the pin 2 and 7 lever switches. What are you using to clean the switches?

Ordinary contact cleaner from Radio Shack or a home center might not cut it. You might need something stronger, like De-Ox-It. Working like a champ now I believe the entire problem from the get-go was the toggle switch contacts. I went ahead and removed the whole gang of them (the group was soldered together by a few stiff buss wires running down the whole length). I was then able to bend them slightly back to gain access to the contacts.

They were some of the worst I'd ever seen. What should have been silver was solid black (even gummy in some areas). I mostly used an eraser, but also a bit of silver polish. As mentioned above, the standard contact cleaner wasn't cutting it. I put it back together and everything works exactly as it should. A very cool tube tester. I went ahead and replaced the one large cap and left everything else as it was.

Replacing the large cap seems to have given the meter a little more range. I really appreciate all the help, everyone's advice was super helpful. Can't thank you enough.