• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

7027a testing

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brucedc

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Joined 2011
#1
Just arrived here and left a short introduction. Looks like a great forum.


This is my question: When I'm out checking on possible tube buys I take my little EMC 213 tester with me for quick quality and short checks before buying. Problem I have is there are no settings listed for 7027/7027a tubes. They will not test properly on 6L6 setting, I assume because of the 2 extra pins. Can someone tell me what those settings would be or where I could find them? I'm having no luck at all..thanks..bruce
 
#2
7027 is electrically the same thing as a 6L6 but has higher voltage / dissipation ratings. You are right about the two pins, that is probably giving you troubles on testing. They would be pins one (1) and six (6). If you have a tube tester that you can select what the different pins of the tube under test see, make sure pins 1 and 6 are NOT connected to anything. Then it should test like any other glass 6L6. The other thing you can do is cut pins 1 and 6 off of the 7027 and then it will test correctly on the 6L6 setting. This will devalue the tube though.
Daniel
 
#5
Sure. Get yourself an octal plug and an octal socket. Using a relatively stiff wire, you can connect the two, with the socket floating about 1 cm or so above the plug. Care must be taken when plugging and unplugging! If you're a real studboy, you'll find some high voltage potting material and make it into a monolithic assembly which will be considerably less fragile.
 
#6
In most cases, 7027 and 6L6GC are interchangeable. Amps with 7027 seldom used pins 1 and 6 (but check!). 6L6 amps may have used pins 1 and 6 as tie points - move these wires to a new terminal and either will work. I don't have an EMC tester any more, but I believe it has a switch corresponding to each pin. Set for 6L6, set switch #6 to the same position as #5, set switch #1 to the same position as #4, and test. Pins 1 and 6 may test "short" - ignore.
 
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