CRT Rejuvination tips and tricks

[bandersen]

I thought it would be a good idea to combine all the tips and tricks on CRT rejuvination. Here's what I've picked up:

• When testing a CRT that's been sitting around for long (years or decades), leave it running for a few hours to wake it up. Using a slightly elevated filament voltage of 8 volts or so can help. Don't rush to rejuvinate it.
  
  
• If a CRT really is weak, try to get your hands on a modern CRT restorer like a Sencore CR70. Older units like the B&K 440 are pretty rough on the filament. Basically, they just charge up a capacitor and discharge through the cathode. A better unit will use a more controlled method.
  
  
• Use the lowest rejuvination mode first and re-test. Only go up to higher settings as a last resort. Each time you try to rejuv. a tube you are blowing off a little more cathode material. Too many attempts and you've got a dead tube.
  
  
• CRT brighteners boost the filament voltage and although they help for a while actually accelerate the demise of your CRT.
  
  
• It's a good idea to add a current limiter (e.g. CL-90) to a series wired set to protected the CRT from startup current surges. If you have the room, adding a separate 6.3VAC transformer for the CRT filament works well too. Just remember to replace it with a 10 ohm 10 W resistor in the series string.
  
  
• If you have an open cathode (good filament but no emission) you can try this technique I got from jeyurkon. It worked fine with my Sencore CR70.

Originally Posted by jeyurkon

This is from the Sencore CR31A SuperMack manual, so I don't know if it works with all rejuvenators.

If a CRT indicates absolutely no emission, and the filament is still working, an open cathode is indicated. When this occurs the automatic controlled REMOVE G1 SHORTS circuite of the CR31 can be used in an attempt to weld the cathode. (goes on to talk about resoldering the pins first).

1. Set the BEAM BUILDER function switch to the REJUV 2 position and allow the filament to warm up for 60 seconds.

2. Set the Function switch to the REMOVE G1 SHORTS position and IMMEDIATELY press the REJUVENATE OR RESTORE button before the filament has time to cool. At the same time, tap the neck of the CRT.

3. If a flash occurs in the CRT neck, release the REJUVENTATE OR RESTORE button. Return to the CRT TEST section and check the CRT for emission. If no flash occurs and/or no emission can be read on the meter, the cathode cannot be welded to restore performance.


John

I'm sure you guys can add more to this thread