Testing the 3-500Z pins

learn the pin arrangement and numbering of the 3-500Z Amplifier Tube3-500Z tubes are the tubes we usually use in our own Ham Radio Amplifiers.  We have always liked them for their power and longevity.  Knowing the pin numbers of these tubes are sometimes important especially when your testing the tubes or working on an amplifier that they are installed in. 

What pin is which?  what is the pin arrangement?... seems to be an on-going question and since we could not find any real information with pictures on the internet we decided to do it ourselves in hopes to help others gain knowledge. 

Lay your 500 Z tube down on its side,  make sure it does not roll away and hit the ground and break!!  ( as two of these tubes are about half the price of an apartment's monthly rent ) you will notice that one of the pins has lots of distance between it and all the other pins, this is pin#3.
If you orientate your 3-500Z tube laying down with pin #3 on the top you will see how the pins are numbered, just like in the picture.... now, you know the pin arrangement and numbering of the 500Z tube, ah, not so hard when you see the picture is it?

Important Safety Information, anything that uses a 3-500Z tube or any tube of this nature uses ultra high voltage and amperage.  Just touching the wrong place on this tube while it is still in an amplifier, even if the amplifier is un-plugged with out properly discharging the stored electrical energy will kill you dead!!.  This is no joke!, if you have no high voltage electrical training and electrical theory training on tube amplifiers, do not ever attempt to remove a tube from an amplifier.  

So you just blew up your ham amplifier and are now wondering if your 3-500Z tubes are still good?

Good question, as I am yet to see a tube tester that you can just plug one of these monsters into and have it test good 800 watts or bad 300 watts, even those old time tube testers tested nothing of this size.  This would actually, be simple to design but I don't think you could make much money testing tubes... but who knows, I am the last person that would try and stop ones entrepreneurial spirit. 

Usually a buddies amplifier will work for testing ( oops laughing ), but if your tube has a filament grid short you can also seriously damage your500Z, 3-500ZG, taylor 3-500 tube buddies amplifier.  So here is my suggestion, before you stick those tubes anywhere!, be sure you at least test them, so you still have a buddy.  With the tube out of the amplifier, first visually inspect the tube for any internal melting, wear or signs of damage. 

Get your handy ohm meter and check pin #1 and #5 for continuity it should have some sort of stable resistance reading.  Heathkit Amplifier Manuals state that if you find a infinite resistance reading on pins #1 and #5 using an ohm meter, this indicates a faulty tube filament. 

Check the other pins as there should be no other continuity reading on the other pins.  If continuity reading are found on the other pins... it's a shorted tube.  Also important to note There shouldn't be any continuity reading from any pin to the top of the tube, known as the plate cap.


you can see why this SB-220 failed due to the funky parasitic suppression modification, this amp arced, sparked and blew the door knob capacitor a bunch of diodes and resistors...not to mention melted rf choke 2Also, it should be noted, that there has been many writings about some tubes will fail under load, yet test correctly using the above method .....but I have not seen that myself.  "I guess when in doubt throw them out or give them to me"....or something like that.  There is no way to test the tube for output at this stage.  The above test is to see if your 3 500Z tube either caused the amplifier to crash or if it survived the amplifier crash and is in still good condition, or has a good chance of still being in good condition.

We have used American, Chinese and French ...just about every Manufactures brand of the 3-500Z tube.  We liked them all and they all work fine.  Now-a-days everything is made in China and its most likely any New 3-500 Z you purchase regardless of the silk screened logo will be made in China.  For the past several years we buy the RF Parts Taylor brand of the 3-500ZG as its a very good tube.

"Life is about Learning and Helping Others as we go"
About me, my name is Sam Moriarity and I am a Ham Radio Operator KI6DTC
We have lots of old radio gear that we fix and repair ourselves.  I am also a Business Owner Billing Pros.Com  in which we have lots of business equipment that we also fix and repair ourselves.  My Father bought me my first radio as a Christmas present when I was 13 years old..., 35 years later and it's still one of my most enjoyable hobbies.  Thanks Dad!

File: 3-500Z Pin Arrangement, Numbering and Pin Testing of the 3-500 Z Ham Amplifier Tube.

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