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Title: 3-500Z's-SOLVED Post by: w3khg on January 07, 2019, 03:52:44 PM 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 Title: Re: 3-500Z's Post by: DMOD on January 07, 2019, 07:08:57 PM 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 Title: Re: 3-500Z's Post by: w3khg on January 07, 2019, 07:28:02 PM 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 Title: Re: 3-500Z's Post by: W1ITT on January 07, 2019, 07:53:20 PM 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. Title: Re: 3-500Z's Post by: KD6VXI on January 07, 2019, 07:57:37 PM I've had 500Z tubes rattle around and still work. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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 |