I haven't watched my 27" Admiral black and white in a while because I know its on borrowed time. The emissions barely read on my tester and I did rejuvenate it once, the emissions were very strong and the picture was great, but that lasted until I went away for a week then the tube was weak again. I'm afraid to keep rejuvenating it because I may kill it. I can't get anyone to rebuild it and haven't been able to find a good used, or new tube. So the other night I bought a brightener and hooked it up to the tube then to my tester and the emissions were pegged, and the cutoff was perfect. This got me thinking, so I disconnected the brightener and hooked up the tester. It's a 6.3v tube around 7-7.5 volts I got the same reading. Looking at the brightness of the filament that has to be significantly lower voltage than the brightener. I feel like I could get this tube to last longer if I could get the voltage down on the brightener. Has anyone done this before? If so how did you do it? I'd like to squeeze every last ounce of life from this tube because I really like the set.

There are variable brighteners like this duz-all

One on ebay: https://www.ebay.com/itm/234860275066?hash=item36aec3657a:g:n8gAAOSwAmdjwzJ Z

https://live.staticflickr.com/65535/53099832536_257cd56590_c.jpg (https://flic.kr/p/2oUfwf5)

Thanks Bob I didn't know they had them. Most of the ones I've s3en are just a transformer.

One of the things I have learned on my B&K 466 is the rejuvenate button is typically kill or cure...But changing the heater voltage is typically cure or no change.
Really weak tubes seem especially prone to sleeping sickness where emissions plumet after a few days to hours of disuse. Running at brightener voltage for 5 min to a couple of days acts like a no-risk rejuvenation so I typically do that before I go to installing a brightener in the set. YMMV.

I once inserted a 5 ohm, 5 watt pot in one of the filament wires coming out of the brightener and dialed the voltage I wanted.