Retensioning Tube Sockets and Preamp Tube Leakage Tests

There is some truth to the old saying "Don't mess with it if it is working." Well, being slightly OCD prevents me from doing that. In this video, I show you how to tighten (retension) the socket contacts.
And, I show you how to test tubes for leakage using an old tube tester.
With amps, I like to check them just to be sure they are working properly. In this case, I gave myself a little scare. I just removed the power tubes to check their bias setting and when I put them back in, the amp would cut out when I would hit a big bass note or chord. So, I ended up taking the chassis out to check everything. It's a pain but I am glad I did. I discovered a tube that may have been bad although the amp was still sounding good. My original goal was to improve the sound of the 1966 Super Reverb as compared to this 1964 SR. I ended up screwing up the sound of the 1964 but eventually got it back to sounding better. These old amps can do that. That is why I love them so much. You can tweak them here and there until you get them dialed in.
I suspected that I had a bad contact somewhere in the power tube sockets because that is all I had touched. It is much easier to check the sockets when it is sitting face up on a bench. It turns out, all they needed was a little retensioning and some good old DeoxIT D100 contact cleaner. store.caig.com/...
Also in the process, I decided to check the old 12AT7's in V3 and V6 which are important and found that one of my old tubes showed some leakage between the heater and cathode. I just happened to have some Philips ECG NOS tubes that I just purchase and they worked perfectly.

[@goodun2974]

Although I have a number of Hickok testers, the 752 (like yours) is my favorite because it's so fast and easy to setup and use (mine is the A version), and the leakage test (read on the meter) is far more useful and accurate than the basic neon-bulb "shorts" test found in most other tube testers, including most Hickoks. It's worth noting that I've encountered a few "leaky" tubes that subsequently measured fine after cleaning greasy gunk from the base and the tube pins with alcohol (NOT De-Oxit!) and a toothbrush. That said, *don't use DeOxit or other residue-leaving cleaners on tube sockets*! Yes, many people do, but it's a terrible idea. The residue can make the socket conductive and/or attract dust and cause arcing, especially in humid weather (400 to 500 volt supplies are always looking for a new circuit path to travel). Use pure alcohol to degrease tube sockets!. Nylon paintgun tip-cleaning brushes can be helpfull (they're cheap from Harbor freight, expensive when marketed specifically as "tube socket cleaning brushes"), however they're too soft to remove heavy oxidation. Work a piece of wound guitar string, .036 to .039, back and forth inside the socket contacts, like a miniature round file, or put a short piece of it in a small Dremel tool, battery-powered pencil eraser, or rotary engraver and let the tool spin the guitar string inside the socket contacts, then flush with alcohol. PS --- NEVER spray the sockets or switches on a tube tester with DeOxit. NEVER! Alan Douglas specifically advises against it in his book on tube testers and test equipment. You can create permanent leakage paths or cause the tester to act flukey, especially in humid weather. I've seen it happen. For cleaning the switches, Alan's advice is to apply a tiny droplet of cleaner exactly, and only, where you need it, using a toothpick or dental pick or similar.

[@millstap]

I read that article about DeoxIT on tube testers. I've not used it there. I am amazed how well the Hickok works and I have never even looked inside to see if anything needs some attention. It may not be calibrated but it seems to be accurate for what I need it for. I've used DeoxIT on just about everything else though. I got the same warning on using it on my Sprague Tel-Ohmike refurbish but I was defiant and used it. Everything went well on that and it's working fine. Thanks for the info on cleaning with the string. I really should replace all of the old sockets. I have replace a few as needed. It's hardly worth constantly fighting those old loose sockets. But, they rarely cause me any problems. And Harbor Freight, I need to go there more often. It sounds like they have something for everyone.

[@sharonlatham7046]

You must be an amp tech or electrical engineer! Thankyou, sir for the info. I used to go with my dad to the Rexall drug stores in the early 60s after he pulled the tubes out of the back of the 'ol family TV and use the DIY testers they all had. I remember the tester was about as big as a washing machine! Dad had to get it running so we could watch the latest Maverick, Gunsmoke, and the 6 'oclock news. LOL!

[@millstap]

I remember even in the 7-11 they had them. Those TV's never worked very well. Always that darn horizontal adjustment. Actually, I had to learn all of my amp skills on my own or I would have gone broke and crazy. I told my wife yesterday how many thousands of dollars I have saved by doing it myself. Plus, you can mess with them whenever you feel the urge. I don't even know of a good amp tech. in my area. That was another reason. I have so many amps I would have spent half a lifetime running back and forth trying to get just simple little things fixed, each probably costing a minimum of $80 (just guessing). The old amps are easy to work on. Forget about it on the modern amps with printed circuit boards.

[@jameshenz1780]

Greetings! I have never heard of a leaky preamp tube. Please explain. Ty for the videos.

[@jameshenz1780]

Vacuum leaks?

[@janhundling4647]

have you ever tried sonus fuzz faces? I think they'll sound amazing with your bassman and strat

[@millstap]

No. Just looked them up and it appears they are unavailable now. I see he uses the original NKT275 transistor. Not cheap at $499. There are so many out there. That one sounds good. I wish I could try one.

[@janhundling4647]

You're right indeed! He also builds some other fuzzes which also seem great, however nothing beats a great amp/guitar like your setup ;)

[@MatthewScottmusic]

I need to send you my amps :/

[@millstap]

It is fun to dial them in and mess with them occasionally. I just put a Mullard GZ34 in my 1966 Super Reverb because I had forgotten I had a Chinese GZ34 in there. It sounds better to me now. Rectifiers do make a slight difference. The tube tester helped me a lot. I don't think I could survive without it. It's not that hard to learn. It was a long learning curve but I am glad I did it. It saved me thousands of dollars and a lot of peace of mind over the years.

[@millstap]

Are you having issues with any of them? I really only mess with the real vintage ones because they are so easy to work on. Leo designed them to be very service friendly. He was a radio repairman in the beginning.

[@MatthewScottmusic]

Yeah I know I could get a lot better sound of my amps, starting with tubes. I'm just such a novice though. To start, my 65 the reverb knob only goes to about 3 and then has a horrible hiss. Real pain.

[@millstap]

That must be the reissue. I don't like printed circuit boards. It could be many things. The simplest thing to try that you can do is to switch out the 12AT7 tube in V3 (3rd from the left when looking at the amp). It's worth a try. After that, it is a matter of looking at everything besides tubes. Tubes are, thankfully, usually the first things that cause problems.

[@MatthewScottmusic]

I'll try that. The reverb issue is in the original 1965.