Recapping a Tektronix 422

Thread Starter


Joined Jan 27, 2015
It's a 1960's scope. I recapped the PSU, but have to recheck them now with a LCR meter. It had a funny regulation 'problem' too, but it could be fine for ll I know. And I never fully load tested it yet, I'll do that soon. I want to recap the scope 1/2 and see what happens. I put it off for too long, and I'm really looking forward to it, with new tools. and on a new workbench.
electrical parts list starts on p126
schematic and diagrams start p159

What quality of elec. caps are really needed for this ? I have some cheap ebay ones and not much else, I did choose their ratings with this scope in mind.

Some of the caps are in sturdy metal tubes, perhaps for shielding and for physical protection. But there are labels on the tubes, so it could be the actual cap is jacketed ? I'll check tonight.

They are all listed in the great Tek422 manual, what key elec. caps should I order brand name caps for, like in the HV section ?

Is there anything in the HV section I should be be worried about. IDK how this one works, is there any potted stuff like voltage multipler's that should be checked somehow ?


Joined Mar 30, 2015
It's a 1960's scope. I recapped the PSU
I have about a dozen Tek scopes from the 70's/80's and several dozen plug-ins. I haven't recapped anything. I only replace components that have failed or deteriorated enough to cause a problem. I have not replaced a single capacitor.
what key elec. caps should I order brand name caps for, like in the HV section ?
Any brand carried by an authorized distributor that has the appropriate voltage and temperature rating.


Joined Oct 2, 2009
Same as @dl324 I do not recap anything unless I know the capacitor needs replacing.
I have a couple of Tektronix 422 and never needed to recap.

Thread Starter


Joined Jan 27, 2015
Ok well I finally took apart the scope section and lifted a leg on all the electro-caps and actually they are all well within ESR spec. When I recapped the PSU section I never had a god ESR tester back then, so I just replaced them all. Now I wish I hadn't, because they looked nicer, or at least there physical size fit nicer and it looked better.

Oh well. But now to figure out if the PSU really works right. Last time I had it running, the square wave multi-vibrator wasn't oscillating at all for some reason. Maybe it's not supposed to when it's unloaded, IDK.

Also either or both (I can't remember), the -12V and +12V regulator circuits were losing regulation at around 5-10Hz or something like that. That was only with loading on the -12V and 12V rails though. So I'll try some more complete load testing.

When I go to hook it up the PSU 1/2 to the scope 1/2, I'll use a current limiter and autotransformer just in case. But it probably works. I think I checked all the PSU transistor's, even the ones in the multi-vib. that wasn't running. I need to check that more IRL and in LTspice I guess.