1950s oscilloscope restoration (help needed)

[Drayson]

Hello everyone, I just received a 1950s WO-33A oscilloscope, and my goal is to restore this thing to working condition. However, I'm not exactly sure where to start.

Spoiler: Pictures

I don't intend on reselling it or anything, this is just meant to be a fun educational project for me, as well as something extremely old to have in my collection.

If anyone has any tips on dealing with ancient tech like this, I'd gladly appreciate it. Thanks in advance!

 

[PT-2]

I'm not familiar with the scope, so just passing on some obvious links:

Manual (specs, operation, maintenance): https://archive.org/details/RCA_WO-33A_Oscilloscope

Rejuvenation project by Chris Prioli, AD2CS: https://web.archive.org/web/2024052...s/1/1/5/5/11554662/ad2cs_rca_wo33a_repair.pdf

And some obvious advice: Be very careful working with high voltage equipment. The capacitors can hold a charge even when the scope is unplugged.

Round CRTs, so charming...

Good luck!

 

[Drayson]

Thanks a lot, this will be very useful

 

[syntax error]

That's a nice little scope. I've got a Heathkit IO-12 a bit bigger than this and an old WW2 British Air MinIstry scope that's about this size.

It's been damp. The first thing you want to check is the transformer for shorted and open windings. The high voltage for this CRT is around 1KV, and the transformer winding is rather delicate. First check it with an ohms meter and then isolate it and give it some power and vheck the voltages.

The main filiment winding will be 6 volts, and another filiment winding for the 6x5.

There will be a B+ windings with a centertap to chassis ground. From groundmI'd guess at about 350 volts at each leg of the B winding. One side of the B transformer then goes further into the high voltage leg. There should be somewhere around 900 to 1500 volts for a 3" tube. Most likely close to 1000v

Outside of the transformer being dead the rest of it will be easy to work on. Spray the controls down with WD-40 and let it soak in.

All the capacitors need to be changed. They're all the same stuff we're using in antique Radios and TV's. They might cost about $20 to change. There's likely some carbon resistors that are drifted as well.

Be careful when probing around 1KV is not plesant to come in contact and you will dance. Watch around the intensity and focus control terminals as this is part of the high voltage circuit.

 

[PT-2]

Thanks for sharing your experience and insights, syntax error!

 

[syntax error]

Glad to help out!