Tube Socket Maintenance

I returned from holiday break after being out of town for about six days.  This morning the right, front KT-120 in my ST-120 wasn't setting up properly on bias adjustment and I even slightly wiggled the tube in the socket to see if bias jumped (didn't see any large jumps).  I got it close at the 12 o'clock bias pot position and recheck bias later on and was on the low side while the other tubes were normal at their customary 10-10:30 bias pot positions.  But I noticed the heater glow on the right, front tube was dimmer than the other KT-120s.   Swapped tubes and the problem followed the position/ socket.  So took the amp down to adjusted the right channel sockets pin tension - especially the heater pins.  That seemed to help and restore normal operation.   Other ohmmeter checks like measuring the 10 ohm cathode resistors, heater wiring, etc looks OK.

Besides re-tensioning the pins are their any cleaners that are safe and effective?   Is there any other maintenance you can do to help prolong the life of the tube sockets?  I have to admit I auditioned a few sets of tubes early on but not for a while now.  The amp is exactly 2 years old and NEVER sounded better after the socket tune up.  What a beast!!!    Thanks for any tips and tricks, Scott

I use pipe cleaners. A couple drops of D5 on one so it's just damp, do the old in and out a couple times to spread the cleaner evenly, then insert and pull the tube itself a couple times to polish up the mating surfaces. Pull the tube and use another pipe cleaner with a bit of ISO on it to remove any excess cleaner and you're golden.

Used tubes can have a lot of corrosion on the pins - a bit of 00 steel wool with D5 and otherwise the same steps to spiffy them up. Even NOS that's been collecting dust for a couple decades can benefit from a quick cleanup. New tubes SHOULD be clean, but who knows?

Been said before, but worth repeating. Never rock the tubes in the sockets and not a bad idea to at least eyeball the socket fingers any time you switch tubes. Pin diameter can vary a bit from brand to brand. I know my TungSols can stretch the sockets to where most KT88's are too loose. I've got a nice little ceramic screwdriver that's perfect for re-tensioning, so I just go thru the sockets when doing a swap. You're not really bending the metal enough to worry about stressing it.

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Belden sockets are my preference.  They have superior grip compared to ceramic sockets.

Thanks... I have a game plan and thanks for the good information.

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I just bought some Beldons. The pins are so tight that I can't get tubes to go in. I guess I'll need to practice some more.

Mine were purchased from Parts ConneXion. I think Jim McShane may have them as well.

Octals
https://www.tubesandmore.com/products/P-ST8-209MIP

9-pin
https://www.tubesandmore.com/products/P-ST9-601

Belt on sockets ... I hear all the cool audiophiles are wearing them ...



I wouldn't try forcing a tube if it's a tight fit as you can stress them and cause vacuum leaks. I use a small nail set tool to stretch mine a bit if they're fighting me. Doesn't take much ...

As a preventive maintenance measure, how often should tube sockets and tube pins be cleaned? I'm not a tube roller, except for rectifiers   , and just want to avoid problems related to corrosion. About two months ago, DeOxit was used to clean sockets and all tube pins in the ST-120.

Captain Coconut wrote:I just bought some Beldons. The pins are so tight that I can't get tubes to go in. I guess I'll need to practice some more.

Mine were purchased from Parts ConneXion. I think Jim McShane may have them as well.

Yes I do, thanks for the mention. And I recommend them highly. I wish the octals were available in a smaller diameter, but the 9 pins fit a lot of places.

Looks like general consensus on process of cleaning tube pins and sockets. What is the recommended interval to clean tube sockets? I'm a believer in periodic maintenance, but I'd rather be listening to the ST120 than working on it!

Thanks,

Gregg

Gregg,

Whenever you change tubes you should tighten up the socket contacts and clean them.
You and I like to roll rectifiers tubes and I've had to retighten that socket much more often. Otherwise I have issues with the heater not lighting up.

I have an ST70. My EL34s never leave the socket and I've had no trouble with those.

Tim

Appreciate the info. My ST 120 is working perfectly and sounds great. In 3-4 months, I'll clean the rectifier pins and sockets. Just for grins, I've ordered a Mullard 12AT7 equivalent for the driver board from Jim McShane, a Christmas present to myself...

Gregg,

Planning on changing the 5v3A to something else in 3-4 months?  What's the next tube?

Hope to reinstall the same 5V3A that's in the amp now. If it ain't broke, I'm not gonna fix it! But if something new comes along, well, maybe.....

If you don't remove the 5V3A, there shouldn't be any need to clean the socket. Removal and reinstallation flexes the contacts.