[Amps] 3-500Z not lit

Artek Manuals Manuals at ArtekManuals.com
Mon Jul 1 09:23:12 EDT 2019

This is becoming a common problem with older 3-500Z amplifiers. These 
tubes draw 15 amps of filament current. Over decades of operation the 
tube pins become quite warm and eventually the springs in the sockets 
loose tension. As they loose tension the contact resistance builds up, 
as the contact resistance builds at 15 amps the contacts  heat up to the 
point of losing some of their temper even more and the process 
accelerates until the tube pin/ socket combo are hot enough to melt the 
solder in them which runs out. This happened to both the 3-500Z's in my 
TL-922A  over a period of months to the point that I replaced the 
sockets. Re-soldering the pins on the 3-500Z is not always easy as the 
fore mentioned process oxidizes  the actual pin inside the outer socket 
pin  sometimes the point that solder will not re-flow around the pin 
inside the pin very well. I even considered buying a small solder pot 
and starting a small cottage industry pulling the base off the 3-500Z 
and cleaning the "inside" pins and then re-soldering everything with 
high temperature solder ( they may originally have used higher temp 
solder for all I know???)

Good luck finding replacement sockets. The older Collins/Johnson sockets 
were silver plated and even new-old stock are often now black with 
silver oxide. All the newer ones on Evil bay are poor quality Chinese 
knock offs. I bought two sets, neither of which aligned with the pins 
very well. Out of the 4 sockets I found two where the heater clips 
aligned fairly well to the point I felt comfortable they would provide 
sufficient contact to handle the 15 AMP filament current . The grid clip 
portion of the sockets are not as critical.

Been there, done that, got the blisters on my fingers to prove it.


On 6/30/2019 3:41 PM, Joe via Amps wrote:
> Quite a while back, when I had a Henry 3K with a pair of 3-500Z tubes, I had a similar situation.I subsequently traced the problem to the SOLDER running OUT of one of the tube pins..... The socket/Pins of/for the 3-500Z overheated enough to melt the solder from one of the tubes...I reapplied solder to the pin and the tube performed well for many years after that...   IF you have a fan available, you might want to direct some cooler air to the tube socket(s)….
> Good Luck
> 73
> Joe  K5KT
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