Tube tester - Sencore MU150 - socket contamination leakage - cleaning it?

[jamesmafyew]

The reason I said "the sockets" were the culprit, is that I disconnected all the wiring from the sockets to the rest of the circuit. So in the schem, I disconnected the wires between the plate switch (S1) and the sockets, as well as the filament wiring (black & brn/black) from S3 and S6 and T2. Totally isolated the socket panel.

In that state, with the sockets and their wiring just hanging there, not connected to anything, the 8050A meter still registered the same leakage among the sockets. No leakage detected among the switch contacts. Powering the unit up with sockets disconnected like this, the tester itself detected ZERO leakage in any switch position. So the phenolic switches don't seem to be the problem, it's either the sockets or socket wiring or both.

I can't do more testing on this right now, because of course now the humidity is around 45-50%, so the whole thing is working just fine.

[soundguruman]

Oh wow, she is cute. Thanks for the memories.

If your sockets are acting up, just put in new sockets.

[olddawg]

I would be tempted to find a can of old non-residue tuner cleaner, wrap the area around the socket with a towel, and spray it down. Then I would heat it up with a blow dryer. That stuff really displaces water.

[jamesmafyew]

I would be tempted to find a can of old non-residue tuner cleaner

Brand or product name?

[soundguruman]

I would be tempted to find a can of old non-residue tuner cleaner, wrap the area around the socket with a towel, and spray it down. Then I would heat it up with a blow dryer. That stuff really displaces water.

There is no magic cleaner that fixes defective tube sockets. You can clean the contacts, that's it. (alcohol works for that) You can tighten the contacts by bending them slightly.
If the socket is leaking, arcing, otherwise defective, it's JUNK.
A new socket costs $3.
When you spray any type of cleaner in there, (that's spray cleaner in a can) it causes water to condense in the socket, because it's very COLD.
So, get a new socket and be done with it.

[olddawg]

Brand or product name?

There are a lot of names. Most shops have a can laying around from the old days. The best was TF solvent but it's illegal to sell now. Just make sure it is the non-residue (no silicon) type and has the small tube applicator. It may not fix it but it will do no harm and you have nothing to lose by trying. It will float away grease, oils, suspended carbon residue and displace water. I would say it's worth a shot. If it doesn't resolve the problem I would look for a ceramic replacement.

Btw.. It's a good idea to a needle or a small medical syringe to apply some Caig to any electrical contact points after using tuner wash. I also do this when rebuilding pots and switches for restorations when replacements aren't available.

[km6xz]

OK, good, I did not remember or understand that you had done that to isolate. There are many sockets in parallel so any one of them might be the culprit. Since it acts up when humid(for that matter, it is just a matter of time before everything in the shop will similarly be corroding so the idea of a dehumidifier/air conditioner was not a joke, it ought to be a priority for high humidity locales), note whether it varies with humidity or simple appears or disappears, at the same level on the panel meter.
I think in you position, I would probably first try to isolate further by finding an approximate mid point of the wiring of the grid lines and break the connection, to divide the sockets in 1/2. If it stops you know it is in the part that is past the break. If it is just as high, it is in the fist part. And progress by dividing in 1/2. If there is no abrupt change, but a gradual decrease in proportion to the ratio of in-circuit to out of circuit, that almost eliminates "a" socket but a system fault. It would be impractical to shotgun the whole thing and replace all the sockets because some are not readily available anymore but you could bypass those which are not used in your work, like I do not suspect you use many loctal tubes in audio...they were terrible for noise and microphonics even though designed for ruggedized mobile applications such as car radios.
You have used alcohol with is certainly a good solvent but many contaminates are not cleaned by alcohol so a multi-step process of using the main organic solvents one at a time, drying thoroughly between steps. Alcohol is "dry" and absorbs moisture if the alcohol is in fact dry. The rub is that it seldom is in a shop situation where the bottle is opened, the drier it started the faster rate of absorption that occurs. For general cleaning and water suspention purposed store in smaller bottles and closed at all times. Flush areas, like a wash so that suspended water is washed away. Cleaning areas with a brush or Q-tip might remove dirt but it might not flush contaminated alcohol-suspension water away. In the old TV repair days, techs would use Tun-O-Wash or other spray solvent that would be projected in large volume and moderate pressure to flood an area. For moisture flushing that really worked. Labs had vapor recovery hoods over washing tables that allowed flooding circuit or assembly with solvent.
If a strong solvent is used, it might leave the contact surfaced open for rapid corrosion so "contact cleaner" becomes the worst possible solvent for electrical contacts because they are too dry, allowing rapid oxidation. So a tiny amount of DeOxit needs to be applied(not sprayed) precisely on the metal contact surfaces to prevent oxidation after cleaning.
If the contaminant is fat soluble, water and alcohol will not be very effective. You could clean with ether in that case.
Good luck

[jamesmafyew]

That's super helpful, thank you.

[km6xz]

What? Julia;s photo or the hints on isolation and solvents;>)