[R-390] OT: Low-voltage tubes

[Scott, Barry (Clyde B)]

I recently had to have a Zenith TransOceanic.  This is the H500 model so it
is still tube stuff (except for the selenium rectifier).

My question is do these low-voltage tubes glow very much?  These are types
1U4, 1U5, 1L6, and 3V4.  I put them in my tester and did not notice any glow
but without the glow, some still tested okay.  Is this just a characteristic
of these tube types?  I realize this radio was meant to run off batteries so
the enery consumed in lighting the tubes had to be minimal, but I was
wondering if I should be able to see anything when they are operational?

Thanks,

Barry(III) - N4BUQ