How to Fix Those 3-500Z's Filament Pins [solder dripped out]

[K1JJ]

Today I turned on my Schmega 3-500Z linear and found [yet again] one of the 3-500Z's didn't light up.  This is the amplifier that I added a blower to the bottom to pass air by the pins. It was a basket case amplifier I acquired that does not have chimneys.  

Anyway, in the past I had resoldered the tube pins a few times, but for some reason they were still intermitant, even with good cooling on them.  The excessive heat originally caused the solder in the pin/wire connection to fail and it needs to be repaired properly or will fail again, even with good air..

I heated the pins up with a torch and added new solder. Put them in the amplifier and the filament was still dead. Tried is several times more, and even measured it with a VOM... but when the "juice" came on the filaments didn't light. I heard a quick spark indicating a poor connection that opened again.

I figgered that the old solder in there was "piss solder", the kind you see when there's a cold joint and it looks rough and dull. It was blocking the new solder flow and needed to be removed...

So here's what I did:

I heated the heck out of each pin. Don't be afraid to apply lots of heat to the pin with the propane torch. Shake the tube up and down until the old solder drops out. Stick a fine steel wire in there to break up the old solder.  THEN while the pin is still hot and the solder remaiining is still  melted, grab the pin with a pair of pliers and gently twist it to free it from the inner wire that goes into the tube. This step is important, cuz I tried just resoldering the pins without twisting it and no good.  It appears that the pin and inner wire have to get a fresh start with no remaining solder and blockage. After twisting the pin, shake the tube once more to empty any remaining solder.  [MAKE SURE the solder is still melted before twisting the pin or you could twist the inner tube wire off]

Then heat the pin and flow new solder into it until full. Worked like a charm.

After many tries without success in the beginning, I had nothing to lose, so really poured on the heat from the torch. I was amazed at how hot the pins could get without damaging the seals. You will probably not have to do it as many times as I did, but I just wanted to say that those tube pins can take a lot of heat. One guy told me he was hesitant to do this because of this fear, but it appears OK.  

As a final check out, I put 10V DC on the filaments for a fraction of a second to make sure the new connections could handle the current. [twice the normal  volatge] It passed.

I know there's some bad 3-500Z's out there.  [Dino!]  Let me know how you guys make out.

73,
Tom, K1JJ

[K1JJ]

In hindsight, I think a good quality solder sucker would pull that old solder out even better. An electric vacuum commercial version would be ideal.

Also, it occured that maybe a higher temperature silver solder might be in order for replacement. However,  maybe the lower temperature standard solder is a better idea, since it acts like a fuse. Maybe the temperature on the pins has no business being high enough to melt solder in the first place...  A check of tube pin engr data max operating temperature could tell the story.

T

[W2VW]

Sometines the filament pin clips on the sockets develop low hanging BA's. Encountered that on the ceramic Johnson 4-400 sockets and 813 sockets.

[WA1GFZ]

Tom,
You should invest in some solder wick. High quality stuff has a lot of flux
to pull the old solder out. Flame could tarnish the pin and it could never flow. Sounds like time to replace the sockets too. Maybe the contacts are not gripping the pin so there is heat due to a poor connection.
You might want to find some high temperature solder that flows at a higher temperature. 3% silver or something with more tin content.
New plumbing solder has no lead and takes more heat. You will have to use a little flux with it.

[KA7IUS]

Hello,
     I had some problems (on my van,) with a computer modual. When eliminated the plug-in connecter that had some pins corrote away from this fine road salt that they use in this state.
     It worked good for a couple years, then one summer day the solder driped out of the connecton, while I was on the hiway and the engine was hot. I resolered it (all 47 connections.) Used the new plumming solder, some flux, and a 500 watt iron.
Tony