------------------------------
 
Date: Sat, 5 Feb 94 12:26:50 EST
From: mblisd!isdserv1!chrism@Aus.Sun.COM (Chris Mouzouris)
Subject: DIY: Rejuvenating Tubes/Valves

Whilst looking through my old electronics magazines searching for a circuit for
a good headphone amp, I came across a story which may interest some of the tube
enthusiasts in the group. It is essentially about a serviceman using a device
designed to rejuvenate old black and white CRT's, to rejuvenate a 6V6-G tube 
from an old console radio. I can't make any personal claims for the methods
outlined below (ie. use at own risk), as this sort of thing is out of my league and besides, I am very happy with my solid state amplifier <g>. 

The interesting bit from the story (Electronics Australia July 1991)------

"These 'CRT rejuvenator' devices where at one time quite common about the 
trade, and generally consisted of a filament transformer tapped at 6.3V, 7.5V
and 9V, together with some form of HT supply around the 200V mark.

Mine was constructed in an old wooden meter case, with a set of flyleads
emanating from one side, terminated in an eight-pin CRT socket. When fitted 
to the picture tube, all the elements were tied to the positive side of the 
HT supply through a 15 watt 240V (Australian) lamp. The cathode of the tube
was returned to the negative terminal.

The front panel was rather unimpressive, consisting simply of a filament
voltage selector switch, an AC switch to the filament transformer only, and 
a means of viewing the lamp. There are probably as many versions of this
device as there were methods of using them, hence I make no claims for my
own system other than to say that I used it often, with excellent results.

In operation, the HT supply remained on for the duraion of the rejuvenation
and the filament voltage turned on at the lowest tapping, while watching the
lamp for any sign of redness. Usually nothing happened and one then tried
the 7.5V tap, or if necessary the 9V tap. At first sign of a glow, the AC 
supply to the filament was cut until everything cooled down, then the process
started over again. The object was to have the lamp glow on the 6.3V setting.
At this point the low emission is cured, and the tube should perform like new.

On this particular occasion we set up the experiment on the kitchen table and
connected the 6V6-G to the socket with jumper leads. The valve responded very
quickly to the treatment, for in only a few minutes I felt confident in 
pronouncing the job a success. But proof of the pudding came about an hour
later, when a phone call confirmed that the old radio had '...never sounded
better!' So for enthusiasts doing a restoration and finding themselves stuck
in this manner, I can only suggest 'Give it a go!'. 

For low power valves, and also for mini series types, it may be wise to use a
higher ohmage load than the one I have described. The characteristics of an
incandescent lamp are ideal for this application, since the resistance will 
increase with temperature (brightness) - thereby offering a fair degree of
protection over that from a pure resistance."

--------------------------------------------------------------------------- 

Hope this is of use to someone.
 
Oh, if anyone knows where I can get a good kit for a headphne amp, I 
would appreciate it if they could let me know the details.

Regards,

---------------------------------
Chris Mouzouris
Email: mblisd!chrism@aus.sun.com
---------------------------------