Tubes Asylum

Posted by AJ (A) on June 22, 2008 at 18:22:03

Hi all,

Some time ago I bought a pair of in circuit current meters used in television servicing for sweep tubes.For a couple of bucks a piece a got 8pin sockets and a small chassis.

I put together a bias meter set with some surplus millliammeters from the spare parts. I was always curious as to accuracy of the Marantz unit as time goes on and don't always want to peel open the the bottom to check bias for certain. The top mounted meter is actually accurate you can see in that each tube sits at 50ma in the model 5 , Spot on spec to the chassis meter ... However, I can check amps that don't have built in bias meters or satisfy my curiosty. It allows you to watch bias on 4 tubes at once over a long period of time. This is great for the deuce as its built in meter is of dubious quality any way. I did set up the current meter x4 on the citation and let it burn in to check bias over an hour or so.

Commercial units are available but this was a very simple project for not much money <$20.00

You may want to give it a try.. AJ