6U5/6G5 Tuning Eye Tube Questions

[Captainclock]

Hello everyone I have a question concerning the 6U5/6G5 Tuning Eye tube, for some reason or another I've noticed that when I was working on a late 1950s vintage Magnavox Console (yes the one I accidentally broke the tone control on and that the record player was seized up on so bad that I ended up breaking the speed control knob on it), anyways I noticed that before the tone control broke on it and what not that the tuning eye tube on it responded very well to signals and glowed nice and bright, but then when I gave the unit back to the guy for him to get rid of because it wasn't worth fixing without having to spend a ton of dough trying to hunt down a new tone control switch that may or may not be a proper replacement and having to hunt down a new record player for it, etc, I bought the tubes from the unit off of the guy and I went to try the tuning eye tube from the old magnavox console in my old Well Gardner console from the early 1940s which uses the same exact tuning eye tube as the old magnavox did I noticed that the tube didn't glow as brightly in the Wells Gardner console as it did in the Magnavox and I'm wondering why that is, because the tube is a perfectly good tube yet but yet it don't glow very brightly inside the Wells Gardner Console vs how brightly it glowed in the Magnavox console.
Does anyone know why a tuning eye tube would glow like its supposed to in one radio but not in another radio?

Any info would be appreciated.

-Levi

P.S. the Wells Gardner Console was completely recapped whereas the Magnavox wasn't, so I don't know if that would make a difference or not.