Re: 577 D2 question(s)


ChuckA
 

I've had good luck using a Sencore CR-70 restoring  a TDS-648A and a HP3562A CRT, both were so dim as not usable.

Running the filament about 40%-50% higher for a time was a old method to sometimes make a dim picture tube in early TV's come back to life for a short time. TV brighteners were common in late 40's and early 50's to extend the life of a TV, they had a small autotransformer and ran the filament at around 8V.

Chuck

On 5/5/2021 11:05 AM, Andy Warner wrote:
Thanks all,
I was hoping it would not be the tube, I have been lucky enough to
avoid that on my other Tek gear.
I'll take a pass at the HV board first, but it sounds like I likely have a
poisoned cathode.

Any reason I should not try a full rejuvenation - including applying some
current limited HT between cathode and grid, or is there a reason you
suggested just overdriving the heater, Bob ?

From the serial #, my unit has the 154-0633-10 tube, which appears to be
unobtainium - sigh.

On Tue, May 4, 2021 at 10:33 AM <robeughaas@gmail.com> wrote:

The symptom is known as "double peaking" and indicates the CRT has cathode
interface, AKA cathode poisoning. The CRT is near the end of its life.
Applying 12 volts for 10 or 15 minutes to the filament (with the instrument
power off, since, in operation, the filament is at -3400 volts), may effect
a temporary repair. Access to the filament is easy via a two-pin connector
on the HV/deflection board.

--
Bob Haas





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