The CR70 has 2 functions REJUVENATE and RESTORE.
From the manual:
In REJUV function, cathode and G2 are tied together. Normal filament voltage is applied and a 1K ohm resistor is in series with discharging capacitor to limit surge current. Pressing REJUV, G1 is positively biased, allowing a sudden surge current to flow from cathode to G1. This current quickly drops to zero, removing the bias on G1. This current surge cracks any coating or removes any contamination on the cathode, allowing cathode to supply proper emission current.
There are 3 levels of restoration. Restoration brings new emitting material to the surface of the cathode by removing old material. In AUTO RESTORE the CR70 cycles the beam current 3 times, in MANUAL RESTORE the tube will draw current as long as the button is pressed. In AUTO and MANUAL 1 current is limited to 100ma, MANUAL 2 current is limited to 150ma.
The filament is increased 50% to superheat the cathode and soften the old material. Cathode and G2 are tied together, places zero bias on the tube and allows maximum current to flow. No current flows until 230 volts is applied to G1. This large current "boils off" the poisoning material, allowing new emitting material to come to the surface. Maximum restoration is reached when all new emitting material is exposed and is indicated as a peak current reading on the CR70 meter.
I've only had to use the RESTORE function on the weak tubes I had to get a usable display.
The REJUVENATE function can be brutal, I have completely killed a couple of picture tubes using this function more than once on a really weak tube.
Chuck
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On 5/6/2021 2:54 AM, Martin wrote:
Hi Chuck,
do you, or anyone else, have an idea what the Sencore and other rejuvenators are actually doing?
cheers
Martin
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