[R-390] General R390 Help

[Roger L Ruszkowski]

Leroy,

If you have to part with a 100.00 or so AUS or US for a tube tester for
your R390.
why not hack an old 5 tube AM radio and a meter into a tube tester?

If you can find a 12 volt filament transformer with a center tap (6.3) and
a 100 - 300 volt B+ winding you can build a tester.

As you only need to test a select number of tubes, you can wire one socket
for each type. A couple switches for the dual triodes can be keep it
simple.

Testers are relative. You can look at the tube manual (on line some where)
and find the expected current for a grid voltage.

Most testers tie the tube up as a triode (for short tests) and vary the
grid voltage to get a mid scale meter reading.

The real test for R390 or A tubes come from use in circuit and judging
the noise. These are all relative test. This one is better than that one.
And you use the best of what you can get. The exact value is not known.

Most tube testers just weeds out the shorts and real dead emitters.

Roger.