Looking for a Tube tester.

[Metalhead]

I bought an old Maco 750 and it has a tube that is not lighting up and want to replace it. I would like to get a tube test to test the tubes also the tubes are M2057. I see tube testers all over Ebay, but I don't know what kind of test to get to test my type of tubes.

 

[Shockwave]

Is the tube cracked? If not, it's likely not making a good connection in the socket. The M2057 is exceptionally difficult to find and I've never seen a tube tester with it listed. Although you can test them as a 6KD6, with the filament set for 12 volts.

It's worth mentioning the M2057 tube has two pins tied to the cathode and some 6KD6 tests may attempt to apply filament voltage across the internal tube connection. I think the pins are 2 and 7. Check them with an AC voltmeter before inserting the tube.

 

[nomadradio]

Tube testers are pretty much all old stuff, decades old. This creates a dilemma that faces everyone who craves a car that old. You can get a derelict cheap, or a restored one for big bucks. Not a lot in between to be found.

There are exotic new testers that only accept a handful of audio or guitar-amp tubes, but those won't check a 2057. We use our tester setup for type 8950. That's basically what a 2057 is. The heater voltage is listed at 13 Volts, not 12.

For that matter, a tester that lists 6KD6 probably has one separate knob to set the heater voltage. Just ignore the 6-Volt setting shown on the setup chart, and crank it up to 13 Volts. Should respond to the same test, except for the heater voltage.

The question arises, which will cost more, the tube tester, or the cost of restoring the 45 year-old linear?

73

 

[Metalhead]

Yeah, it seems to be a money pit.

 

[linearone]

Is the tube cracked? If not, it's likely not making a good connection in the socket. The M2057 is exceptionally difficult to find and I've never seen a tube tester with it listed. Although you can test them as a 6KD6, with the filament set for 12 volts.

It's worth mentioning the M2057 tube has two pins tied to the cathode and some 6KD6 tests may attempt to apply filament voltage across the internal tube connection. I think the pins are 2 and 7. Check them with an AC voltmeter before inserting the tube.

@Shockwave i feel like i read a very old post from you, or perhaps @nomadradio about using tube testers to test big boy tubes, like 8877, 3x3, yc156, 35b etc... obv you need to supply the filaments in an outboard manner but cant you hook up these large tubes to a hickock or similar and get a meaningful result?

 

[Shockwave]

@Shockwave i feel like i read a very old post from you, or perhaps @nomadradio about using tube testers to test big boy tubes, like 8877, 3x3, yc156, 35b etc... obv you need to supply the filaments in an outboard manner but cant you hook up these large tubes to a hickock or similar and get a meaningful result?

This is correct. I took the base off a 811 tube to repurpose the socket. Soldered three wires into the sockets filament and grid pins. These wires attach to a 3-500Z socket that has an outboard filament transformer to run the tube. As I recall I am using the 811A test and adjusted the load for 100% on a new tube. I also left one of the filament pin switches open on the 811A test, to prevent bucking the testers internal filament transformer.

Another 811A socket just has 3 wires connected to alligator clips for testing other tubes that have different filament requirements. These tests don't seem dependent on plate connection and only provide an indication of emissions. It tells us little about breakdown voltages or leakage. The complete test would require passing Hi-pot too.

The largest tube I've tested like this was a 3CW7,000. Any triode I could light and compare against a known full output tube, has been tested like this.

 

[nomadradio]

So long as you supply heater/filament voltage outboard from the tester, this should work. Long wires from the adapter's socket to the socket on the tester could be an issue, making an accidental RF oscillator out of the setup. Bypass caps and ferrite beads are the solution found in every external adapter I have seen. My older Hickok Cardmatic testers didn't have 9-pin noval or 12-pin compactron sockets. But there was an outboard adapter, and a test card with the setup, including where to set a rotary switch on the adapter.

Sold mine when I upgraded our tester. The same principle should apply, you just won't have a way to judge a tube's power-handling capacity at the tiny currents the tester uses to measure gain.

For a directly-heated cathode you might need a trimmer pot to 'zero' the AC voltage at the filament transformer's center tap. Since 60-Hz AC is what's used to feed the tube's grid for measuring gain, any imbalance in the filament center tap would introduce an error.

Drew up first plans to test 3CX800 triodes and 8875 triodes this way, but that project fell off the back burner, still stuck between the stove and the wall.

73