Hi all,

I am currently in the process of restoring a B&K 700 tube tester. I have replaced all electrolytic caps and have calibrated the unit. I have noticed that the meter movement will swing erratically when reading a test result. This only happens when I try and read transconductance results. The needle will jump from side to side whenever I try and read the test result. It doesn't swing more than about a centimeter to each side. Any ideas on what could be happening here? I have the same problem with my 707 tube tester too. I wonder if anyone has come across this before.

this is a known problem with both of these Models, and I have both and had the same problem.
there are 2 #55 lamps inside for protection, and to make Explain things simple you need to solder a solid small wire thru the socket of Both lamp sockets center pin AND the lamps at the same time for both M5 and M6, and then somehow solder the lamps outside terminal to the outside Terminal of the Socket.
cleaning the lamps and sockets will not work well, it can help but you will still have the same problem, there maybe a newer type of repair for this but this is the only one that ever worked for me

But don't solder them together, the idea is to make a good solid connection for each lamp to their Sockets.