Re: New 547 owner
Don Lewis <dlewis11193@...>
Give it bath!toggle quoted messageShow quoted text
I've bee washing scopes (and all electronics) for years. The key is allowing time to dry.
We've had over 30 days of 100+ degree temperatures in Texas this summer, ...so 'drying' has not been a real issue.
I am currently refurbishing a 1951, RCA-WO56A scope, but at this age, most vacuum tube test equipment is similar to Teks and HPs.
What follows is my technique. Certainly not sacrosanct, but works for me:
- Get documentation.
- Get documentation if you can that, as a minimum, lists the scope's specifications and tube types/placements.
- Remove the cover and inspect for loose objects, wires, tubes out-of-socket, etc. Triage the unit.
- Make your own drawing of major items on the scope chassis and tube placement.
- Remove each tube individually.
- Compare the tube marking to what is on the schematic and hopefully what is stenciled on the tube chassis.
- Note whether they match or not. Document what they are/ where they are.
- Clean each tube carefully. The markings on the tube are like old fingerprints. They will unfortunately just dust away.
- Get a 'marks-on-glass' pen.
- Write on each tube its' type, if you can verify it.
- Store away all the tubes for now.
- Take the scope outside and protect the transformer opening the best you can with a plastic baggie, saran wrap. etc.
- I then douse the entire scope, top and undersides, with a complete bottle of dishwashing detergent. Get it good and soapy.
- Then power-wash it with a hose and a hard stream of water.
- Get it good and soapy.
- All nooks and crannies, especially the tube sockets and switch wafers.
- Do not concentrate on the transformer areas or openings.
- Once washed, take a bottle of rubbing alcohol and pour over all the slide switches and rotary switches; work them through their positions.
- Not the potentiometers.
- Let it dry. Let it dry thoroughly.
- The key is to let the entire scope dry for at least a week outside in the wind and sun. Turn it once a day, ultimately through all dimensions, so no liquids are left in hidden pockets.
- Be patient. Don't try to cur corners in drying time in an oven, etc.
- Test the tubes.
- While the scope is drying, test the tubes.
- As a minimum, use an ohmmeter to test each tube for filament continuity.
- I have both a venerable Hickok 752A mutual conductance tester as well as a basic Mercury 990 cathode emission tester.
- Use whatever tester you have, but test the tubes.
- Ensure the correct tube came from its' requisite socket.
- Tubes get replaced over 50-60 years. Substitutions are made.
- Convince yourself the right tube is in the right socket and that it tests ok.
- Don't worry right now about marginally-tested tubes. If they have filaments and some life, they may very well work for the design they are in.
- Re-install the tubes after a week of chassis drying.
- Check for loose wires, components out-of sorts, etc.
- Continuity check the power, switch and fuse circuits.
- If the scope uses a two-wire power cord, ohm it out for hot and neutral, and always plug it in accordingly (hot-to-hot; neutral-to-neutral) until you can rewire using a grounded power cord.
- Get a Variac.
- Now we try to reform the old caps.
- I use a Variac through a voltmeter/ammeter to the scope power plug.
- Turn the scope on and apply the first increment of 20vac.
- I start with 20vac out of the Variac and watch the current.
- Note from the scope specifications what the power and current requirements are. Never let this reforming exceed these specifications.
- Of course, if it does, then it's time to troubleshoot.
- Continue on if the current out of the Variac hold to spec or less.
- Be patient.
- I take one full day at 20vac increments (each day). Ultimately, reaching 120vac.
- If you get this far, you can start checking all voltages, ripple and subsequently scope performance and go to calibration.
- Note that this 'washing' process works quite well with modern scopes and even switching power supplies. BUT DO NOT USE THE VARIAC. Just turn it on once it is dry and monitor the ammeter. If current is excessive, go to debug mode.
This probably could have been stated more eloquently, but I was just trying to help; get some thoughts down. Good 'washing'
On Wednesday, August 02, 2017 11:10:47 PM, email@example.com [TekScopes] <TekScopes@yahoogroups.com> wrote:
Thanks for your message.
I will resist the urge to make either a parts unit - my goal is to get the 547 up and running. If I can do that, the 546 may just sit for a while before I can get to it. Too many other pressing projects.
Not sure about giving it a shower - I'm afraid to do it! Though I do have a basement sauna that would probably work well to speed the drying process.
I'll look for your transformers and check voltages & ripple when I return in two weeks.
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