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Put EL84 instead of EZ81

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  • Put EL84 instead of EZ81

    Some years ago (10 years) i re-tubed my 18watt Marshall Clone... The EZ81 looked exactly like an el84... So my ignorant ass swapped it without even reading the tube for an el84...

    Ive sent the amp to 2 "techs" for fixing:

    The first said the circuit looked good, and it just may need new tubes.

    (got home and the amp just didnt sound fixed)

    Take it to a second "tech" and he says, new tubes, didnt tell me what tubes, so i just start ordering el84 and 12ax7. when i find a link to marshall 18 watt bundles...and THEN I see for the first time EZ81.

    I ordered some nice tubes including the correct rectifier tube, can you guys tell me what consequences i may be facing from this big error? what could have been suffering from this horrible swap?

    thanx guys...

  • #2
    Guessing that just the tube suffered since nothing burned.
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    • #3
      There can be several things that could happen, but the real question is did they happen.
      Something like a blown screen resistor or a transformer melt down are pretty cut and dry. There's no shady area there, you either blew them or you didn't. The tubes are about the only thing that cab be degraded by overheating and produce bad sound quality without blowing completely. Maybe coupling caps.

      I suppose you could have a resistor in there that isn't supplying the right voltage but why speculate. Put the new tubes in and find out if it works. If it doesn't you can then narrow down your search. If it does you were handed your ass and got lucky you didn't loose it. Just don't make the mistake again. Tube amps aren't something you dork around with when servicing. Tube amps don't normally survive stupid mistakes. Not sure why you had the tubes out in the first place. The only reason to go in there is when you buy new tubes and to replace them one at a time so you are sure they get in the right sockets.


      • #4
        If the amp is still producing sound, just not great tone, then you dodged a bullet, as you obviously didn't damage any of the components... a Z81 [or a 6CA4] rectifier tube tends to run 'hot' and the EL84, being a power tube, could handle the current load, but not perform the correct function. Replace with the correct tube, and see what happens...I'm betting the sound will be pretty much where it should be
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        • #5
          A rectifier tube is part of the power supply for the amp that converts AC voltage to DC. If the amp is still powering up (with the correct EZ81 tube in it), you didn't blow the transformer, and chances are you didn't blow anything else up either.

          You can take it to a tech and they can check the rest of the amp's power supply section, but again, if it powers up with the correct rectifier tube, thank your lucky stars - you dodged the bullet.

          Next time, remember - just because they look the same and / or have the same number of pins, that doesn't mean they are the same tube or a suitable substitute. Always double-check the tube chart / manual / online (and the silkscreening on the tube itself) before installing any tubes!


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          • #6
            If you look at the difference in pin configurations. There isn't allot that could have happened if you put the EZ81 rectifier in an EL84 socket. The heater pins are the same, the anode does connect and one plate is used. There are no screens. The only thing the tube would do is beam a DC voltage to the output transformer. Its unlikely it would have damaged anything.

            If the EL84 was plugged into the power supply it would see an over voltage between the anode and cathode. The tube is rated for a maximum of 300v and plugged into the power supply it would see 350V and also being run as a diode. I'm not sure that would have damaged the screens but it might overheat the gas in the tube and weaken it. The other pins aren't being used and it doesn't look like anything would have been shorted from what I'm seeing.

            I'd just replace the tubes with new ones to be safe. Those EL84 tubes have a very short lifespan to begin with and you surely don't want a diode tube going bad and taking out a power transformer.

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            • #7
              Based on the pin out it doesn't look like anything would be shorted causing damage to the amp. Nothing in an EZ81 connects to any other pin except for the heaters, which are the same pins for both tubes. Both of the tubes use the same sole pin for the plate so the high voltage would probably be the same there and not cause problems. I'd be surprised if you damaged either the tubes or the amp doing that....just no sound.
              "I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen


              • #8
                ok its almost 10 days this threat was started, main question remains, does the amp work again?