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
NR1DX
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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Dave
Manuals@ArtekManuals.com
www.ArtekManuals.com
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