[Amps] 3-500Z not lit

Victor Rosenthal 4X6GP k2vco.vic at gmail.com
Mon Jul 1 12:48:56 EDT 2019

I have swapped the grid clips with the filament clips. The grid clips, 
since they haven't heated up, are often in better shape. Usually the 
former filament clips still work OK on the grid pins, if you squeeze 
them a bit.

If you find some old sockets at a hamfest, you can take any undamaged 
clips off of them, too.

The liquid silver cleaner that is designed for dipping takes all that 
black silver sulfide (I don't think it's oxide) off real quick.

I put a more powerful fan in my TL922 to keep it cooler.

Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5

On 01/07/2019 16:23, Artek Manuals wrote:
> 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.
> Dave
> 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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