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Thread: Is there a test to know if I have a el84/6bq5,or6aq5 tubes ?can I interchange them?

  1. #1
    Junior Member
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    Aug 2017

    Is there a test to know if I have a el84/6bq5,or6aq5 tubes ?can I interchange them?

    If I put the new el84 tubes in and it turns out it takes the 6aq5 tube,or the ,6bq5, would that harm anything ?The amp has no name,it is stamped 1964 in red on back panel.It has 2 12ax7 preamp tubes ,and it has a ez81 rectifier takes 2 power tubes of which I only have 1 of.the amp does have both transformers.Is there a place I can send the tube and get them to check it out ,& identify it ,and give me 2 replacements.Thanks for any and all help .peace & Love
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  2. #2
    Supporting Member Chuck H's Avatar
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    May 2007
    pacific north west
    Looks like a 6bq5 to me. The 6aq5 is a little shorter. But with one tube in there and no markings I would say there's no way to know it's the correct tube for the amp or even that either tube type is correct. I'll guess it's a 6bq5 though because that's a pretty typical tube compliment. Check the socket wiring to be sure. For 6bq5's the OT primary leads will be on pin 7 and for 6aq5's they will be on pin 5.
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  3. #3
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    Feb 2009
    You don't have to worry about interchanging those two tube types- 6aq5 is a 7 pin tube and the 6bq5 is a 9 pin tube. So, it's not physically possible to plug a 6aq5 into a 6Bq5 socket or vice versa. Of course, there are many other kinds of 7 and 9 pin power tubes, so it's possible that your amp calls for something totally different. Tracing the wires, measuring the B+ voltage, etc. could give clues.
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  4. #4
    Supporting Member eschertron's Avatar
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    Aug 2012
    Great Black Swamp
    +1 to all above ^^^

    You can do some testing with the power tube sockets empty, a good idea if you're powering up a relic for the first time anyway. IIRC the 6bq5 and the EL84 are indeed interchangeable.
    Sometimes it goes without saying, but just to "say it": dangerous voltages are present. Use proper gear and observe safe practices. Have fun!
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  5. #5
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    Aug 2017
    Thanks Chuck I appreciate it.

  6. #6
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    Aug 2017
    Thanks for the information .I will check the b+.Down the rabbit hole .

  7. #7
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    Aug 2017
    Thanks .I will test the pins and see what I get and see if the el84 tubes will work.I Definately bleed out filter caps and work safe with a volt meter on it.This is Definately a lot of fun learning about amps and all the components and what they do and how to to trouble shoot .Peace and love

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