Tektronix 576 HV transformer and other things

[bdunham7]

I recently picked up an older Tek 576 from Goodwill, looking pretty good but in unknown condition operationally.  Got it home and didn't work, of course, and after some futzing with the power supplies it came to life for a short while.  It has any number of smaller problems, but the main issue at the moment appears to be the known issue with the early HV transformer that supplies 225V and 4000V for the CRT.  Apparently the issue is related to moisture absorption in the epoxy pour around the windings.  The result is that as the transformer heats up, it 'leaks' and then the circuit draws more power which causes it to heat up more and then it runs away until the 100V supply that feeds the transformer oscillator cuts out.  That is what happens here, as soon as the transformer gets up around 130F, the current draw rises.  When cold, the circuit draws about 150mA minimum and about 210mA with the CRT as bright as you would ever want it.  Once it gets warm, this increases rapidly until the 100V supply goes into protection at just under 300mA.

My interim fix while I work on the other issues is to put a small fan on the transformer with the HV cover removed.  This seems to work, I ran it yesterday for 8 hours straight with traces on the screen and the current stayed at 160mA the whole time.  Perhaps adding a fan to the backside of the HV enclosure would be a fix.

What I'd really like though is a replacement transformer.  There's someone on tekscopes.io that had some made, but I haven't heard back as to whether he still has any.  Has anyone come up with a replacement for this application?  There is a bulletin and revision from Tek regarding a replacement that is NLA and requires some other mods.  I'm hoping there is a solution other than me trying to custom-wind a 4000V+ transformer.

[PaulAm]

Well, try again, he might be off on vacation.  He was last active on tekscopes around the end of July.  Maybe start a new thread there?

He did a run of these back at the beginning of 2020 and they probably sold out.  Unless you stumble across a NOS spare or get a used one, this was the only source of replacements I have ever seen.