JJ pre amp tube pin diameter, intermittent test results

[roknroll]

I was testing some used JJ preamp tubes 12A$7 the other night and was annoyed by the fact that the tubes were not making full contact in a brand new tube socket (as well as the old tube socket). The reason I installed the new tube socket in the tester was intermittent test results. The problem appears every time I test JJ preamp tubes. When I plug in an old RCA 7025 or similar, there is no problem. The RCA tubes fit tight and snug in the socket while the JJ's wobble around loosely. So, I pulled out my Dad's old micrometer and measured the diameter of the pins. Sure enough the old RCA pins routinely measured 1/1000 of an inch heavier all the way around, than the JJ's.
I have not measure other brands at this time.
Go figure.

[Structo]

Yeah, I have noticed a difference in tube pin diameter but I haven't really noticed JJ's as having smaller pins.

What kind of sockets did you use?

[morcey2]

Yeah, I have noticed a difference in tube pin diameter but I haven't really noticed JJ's as having smaller pins.

What kind of sockets did you use?

JJ had an issue with too-small pins, but that was quite a while ago. How old is the tube? I have an ECC83S from about 6 years ago that has smaller-than-normal pins, but that's the only one that I've seen.

Matt

[dynaman]

If you do a lot of testing, ya might want to get a socket saver. Much easier to yank it and retension its pins.

[selloutrr]

I did have this issue with cheaper sockets but I assumed it was just the poor quality of the contacts they used. Being that the metal wouldn't hold shape or return back to position.

After testing/installed more JJ/Tesla tubes then anything else, sovtek and Tung-sol being a close second. mixed in with NOS for the special/vintage amps. With over 3,000 tubes, I can't agree it's the tubes.

I've never had any problems in the higher quality sockets.
My test sockets are all military/cinch.

It makes a difference on socket life and contact if you use a pin straightener first.

[dynaman]

**Edited for safety!**

[M Fowler]

I got some 9 pin sockets said to be Fender replacements with the small mounting holes and they do not take tubes well at all.

Very difficult to get the tube started and you better leave it in once you do.
Repeat tube placement seems to bend the pin sockets, very strange tube socket to be selling in my opinion.

[ToneMerc]

When it comes to inserting or removing them, I'm not so sure that an only an additional .0005 of radial tension would make a difference in feel. Nevertheless, for giggles I randomly pulled a few new tubes measured pins 1, 4, 5 & 9.

New GT 12AX7C
1: .03960
4: .03995
5: .03980
9: .04000

New JJ803
1: .03930
4: .03915
5: .03895
9: .03930

New JJ83
1: .03905
4: .03860
5: .03915
9: .03865

NOS Syl 12AT7
1: .03970
4: .03975
5: .03985
9: .03975

NOS Phillips(Mullard) ECC83
1: .03980
4: .04065
5: .03945
9: .03965

TM

[selloutrr]

have you tried making the tube fail with solder in the pin sockets to make sure it doesn't flow or cause the solder to break loose and short out the circuit? It would sure suck to have a costly repair because of a mcgyver fix it job on a cheap socket.

Another bad part of doing this.. you are stuck using the same tubes (diameter of pin) because the holes have zero tolorance to move.

[dynaman]

have you tried making the tube fail with solder in the pin sockets to make sure it doesn't flow or cause the solder to break loose and short out the circuit? It would sure suck to have a costly repair because of a mcgyver fix it job on a cheap socket.

Another bad part of doing this.. you are stuck using the same tubes (diameter of pin) because the holes have zero tolorance to move.

Yeah, I only let just enough in to seep past the pin ends. Hundreds of tube yanks haven't caused any probs in the old tester, but too much solder in the wrong place could conceivably break loose.

In hindsight, I prolly should not have even posted that janky fix. I'll go back and delete my post. Too much lead inhalation!!

[roknroll]

If you do a lot of testing, ya might want to get a socket saver. Much easier to yank it and retension its pins.

The socket is a brand new socket saver.

[roknroll]

Yeah, I have noticed a difference in tube pin diameter but I haven't really noticed JJ's as having smaller pins.

What kind of sockets did you use?

JJ had an issue with too-small pins, but that was quite a while ago. How old is the tube? I have an ECC83S from about 6 years ago that has smaller-than-normal pins, but that's the only one that I've seen.

Matt

The tubes are brand new stock, I buy a couple of thousand dollars a year in JJ's.