3-500Z's-SOLVED

[w3khg]

Couple of 3-500Z's have the following etched markings inside the tubes. The etchings read
W6-3869 and W6-6717. What do these markings mean? Year of Manufacture?

Also one has a rattle with a slight shake coming from the inside suggesting something is either loose or broken. I cannot see any objects causing this. What could this be and would it be dangerous to apply power to this tube? Is there a way to check it out before applying power to it?

The tubes have the Eimac Made in U.S.A. shown on the glass tube.

john

[DMOD]

I would suggest a continuity check across the filament to determine if the filaments are intact and then do a continuity check from each filament pin to the grid and plate pins.

These tubes usually fail with a grid-to-filament short and can cause catastrophic meter or power supply problems.

If the tube rattles, send it to the guy who makes lamps out of transmitting tubes.


Phil  

[w3khg]

I would suggest a continuity check across the filament to determine if the filaments are intact and then do a continuity check from each filament pin to the grid and plate pins.

These tubes usually fail with a grid-to-cathode short and can cause catastrophic meter or power supply problems.

If the tube rattles, send it to the guy who makes lamps out of transmitting tubes.


Phil 

Hello Phil
I attached some leads to the Ohmmeter and the tube pins. While checking continuity first with the cathodes, there was continuity,  and then between cathode and grid I rotated the tube sideways and upside down tapping the glass and there was no continuity indicating no shorts. So I guess this tube is good to go back into the amp.

Perhaps "rattle" was not a good term but there is a clear metallic sound when turned sideways and upside down. Your comment would be appreciated.

The letter/number etching is on the bottom cone if you care to comment.

john

[W1ITT]

Many years ago, a friend had a 3-500Z with a grid to cathode short circuit.  Figuring we had nothing to lose, we put clip leads onto those pins, set the tube inside a paper bag...just in case... and plugged the wires into the 120 vac outlet.  A quick flash was seen, the short was gone, and he ran that tube in a Henry amplifier with no apparent problem until a replacement was purchased.  The 3-500Z is one of those creations of man that just wants to work.
As an aside, he had a couple others with "open" filaments.  It turned out that air was insufficient and the solder had melted out of the filament (cathode) pins.  A bit of solder and flux fixed that too.

[KD6VXI]

I've had 500Z tubes rattle around and still work.

I'm no expert, but I believe it's the grid assembly.  Some tubes make more noise than others. It sounds not like metal against metal, but more metal against a porcelain like substance, dulled by the absence of air in the vacuum.

If yours is metal in metal, I'd worry.

Not just Eimac, either.

No guarantees, but I have noticed the same thing.

--Shane
KD6VXI