# JTM45 GZ34 Rectifier Tube



## bluesbird (Oct 30, 2007)

I recently had rewired a jtm45 reissue to a '66 using the old schematic. Replaced the tubes to GEC KT66, and three amperexe bugle boy for ECC83, and I just got myself a mullard black base GZ34. I replaced the solid state rectifier cap with the mullard; however, there is no sound. The rectifier is functional and tested prior purchase, but it simply does not work. Nevertheless, the rectifier tube heats up, so I do not see a problem in the tube. It works great with the solid state cap, but the mullard does not seem to work. What should I do ?


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## nonreverb (Sep 19, 2006)

neno said:


> I recently had rewired a jtm45 reissue to a '66 using the old schematic. Replaced the tubes to GEC KT66, and three amperexe bugle boy for ECC83, and I just got myself a mullard black base GZ34. I replaced the solid state rectifier cap with the mullard; however, there is no sound. The rectifier is functional and tested prior purchase, but it simply does not work. Nevertheless, the rectifier tube heats up, so I do not see a problem in the tube. It works great with the solid state cap, but the mullard does not seem to work. What should I do ?


You say that you just bought the GZ34...Was the tube previously tested by the seller? If so, I'll bet the tube is the problem...


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## Ripper (Jul 1, 2006)

Does it work with the rectifier cap in place instead of the gz34?


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## bluesbird (Oct 30, 2007)

Ripper said:


> Does it work with the rectifier cap in place instead of the gz34?


Yes, it does work well with the rectifier cap. I haven't really tested the tube myself, which I will. I got it from an honest seller.


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## Wild Bill (May 3, 2006)

neno said:


> Yes, it does work well with the rectifier cap. I haven't really tested the tube myself, which I will. I got it from an honest seller.


There is a big difference between being honest and being right! Your seller may believe that the tube was ok. However, if the socket is wired correctly the only explanation is the tube! 

Just because a tube heats up doesn't mean that its working. There's more going on inside it than that.

Still, with rectifiers 99% of the time if they DO light up then they DO work!

First thing is to try another tube. Or try your tube in another amp to make sure it's working. Unless you have access to a tube tester, of course.

If it still doesn't work, I would check to make sure that no one re-wired the socket, or that maybe there's a problem in the pins. To my knowledge, the JTM45 never had silicon rectifier diodes. They used the tube. I'm assuming that you were using some kind of replacement built into a tube-style base. There were and are a lot of these around and they didn't all have the exact same pinout as the GZ34. Someone might have decided to use what they had and just change the wiring on the socket to match. That would mean that you couldn't just pull the replacement and plug a tube rectifier back in but they likely either didn't care or figured they'd just change the wiring back again.

The way to tell is to look at the bottom of the socket, on the inside of the chassis. You will see a little keyway in the round hole of the locator centre of the socket, to match a little 'nub' on the base of the tube. This is how we make sure that the pins on the tube match the socket. The pins are numbered clockwise, from the left of that locator notch.

Pins 4 and 6 should go to the power transformer and are likely red. These are the high voltage AC leads. There should also be two yellow wires that feed pins 2 and 8. These carry 5 volts of AC to heat up the rectifier tube. Then there should be another wire (probably red) from pin 8 that goes over to the 1st filter cap(s) in the power supply, and also the standby switch.

If this doesn't jive with your amp, then somebody's messed with it!

:food-smiley-004:


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