Zenith H2438R "Aldrich" restoration

[bandersen]

A better question might be why are you trying to test a 7JP4? The phosphor on these usually wears out long before the emissions go bad.

All I know is the only tester I have that supports a 7JP4 has a switch that says (Scope -10V bias). I would think that adds negative 10 volts to the grid with respect to the cathode, but have never measured it.

I would try the 440 as is before modifying it.

[timmy]

Originally Posted by bandersen

A better question might be why are you trying to test a 7JP4? The phosphor on these usually wears out long before the emissions go bad.

All I know is the only tester I have that supports a 7JP4 has a switch that says (Scope -10V bias). I would think that adds negative 10 volts to the grid with respect to the cathode, but have never measured it.

I would try the 440 as is before modifying it.

I’m not modifying the 440 I made an adapter and it does give a reading but they all seem to be the same so I thought this may have given me a more truthful reading. I know the cr70 does these tubes. I applied 10 volts in series with g1 and g2 and just raises the needle alittle bit so I left it in series with g2