boosting CRT heater voltage

[Tony Duell]

> 
> Back in the 70's I worked as a Radio/TV repairman and it was a known
> thing to add a boost transformer into old TV's to get more life out of
> the CRT. iirc there were 10,15, 20% taps, cost was not much better
> than crt replacement iirc.

Another trick is to wind a couple of turns of insulated wire around the 
flyback transfoirmer core and connect it in series with the CRT heater. 
If you want to measure the resulting heater voltage, you need a goodRMS 
meter that will correctly measure the very 'peaky' waveform that results.

> Regeneration was to over run even more for a short period and also
> play with the voltages to knock a layer of oxide off. You need one of
> the regenerator tools for that though.

There have been many designs for these published over the years. A lot 
depend on transformers that were reasonably common when the device was 
designed, but hard to find now...

Basically, you over-run the heater (try 8V or 10V for a 6.3V heater) and 
then apply a high-sih DC voltage between the cathode (-ve) and first grid 
(+ve). The idea is to get a high emission that will strip th etop layer 
off the cathode, exposing new emissive oxide.

You need a few hundred volts. A 'butchers trick' was to use half-wave 
rectified mains witha 15W pygmy bubl in series (!). I won't say any more, 
if you can't work it out, you don't know how to do it safely, if you can, 
then you probably will realise why it's not that good an idea :-)

The problem comes if you strip off too much oxide and leave a totally 
non-emissive cathode. New CRT time :-(. Also modern CRTs have a much 
thinner emissive coating than the ones of 40 or so yeara ago, and tend to 
tkae much less rjuvenation. 

-tony