532 amp and 12AX7 tube

Some of you may remember last October, my Wurlitzer 2150 started acting up. The volume would go very loud, then drop back to normal, then loud and so on. The fix was simply replacing the 12AX7. I say 'the' since my amp only needs one. When I had it re-capped and converted to handle a ceramic cartridge, the person that did the work also 'removed' the auto volume leveling component. (I am now running a magnetic cartridge through a phone pre-amp)

Anyhow, the other day, it started to do it again. Turn it on, gets loud then normal then loud. After several songs it seems to stabilize. Well, I replaced the 12AX7 and all is fine again. My first tube was Russian, this last one was NOS Sylvania made in the US of A. Long build up but my question is whether this (the need to replace this tube every 9 months) is normal or if it symptomatic of some other issue that I need to address. It's not like the tubes are hard to find or expensive, so if that is just the way it is, no problem. However, I would hate it to be masking some other issue that could turn out to be more significant (read expensive), which I could easily mitigate now.

Thanks
Brooks

Hi Brooks,
That's almost--no, it is, a "chicken-egg question". When you can answer my question about how long a new lamp I just installed, will burn, you should have a good idea as to the correct answer for your question ! I doubt there is any ongoing problem--
There was a batch of EH 12AX7's several years ago that were all bad-some would operate for a short time then "act-up". -I don't recall the code date but I think they had a 10 in that date-- Ron Rich

Ron Rich wrote:Hi Brooks,
That's almost--no, it is, a "chicken-egg question". When you can answer my question about how long a new lamp I just installed, will burn, you should have a good idea as to the correct answer for your question !

Well, that's actually easy to answer. It will burn out at the most inopportune time possible. Night time, running very late, need to leave a light on, flip it on as you are running out the door to catch a plane... poof, there it goes.

(Thanks for easing my mind that I don't have some lurking issue....Brooks)

Brooks, I tend to agree that this is "just a fluke" -but, it is possible that in fact nothing was wrong with either tube and it was a bad solder connection on the board and replacing the tube temporarily improves the connection. One test would be to install the first failed 12AX7 and see what happens.

As for how long tubes last..the answer is -very- long in juke amps. I have a lot of original RCA, GE and Tung-Sol tubes running in my commercial machines and they still test adequate after decades of daily use. Many were in those machines when I bought them 20-30+ years ago.

The exception to this are thyratrons such as 2050 and 2D21 which I eliminated for reliability's sake over 25 years ago.

Rob-NYC

Could also be a poor connection, within the tube socket ?? Ron Rich

Dirty corroded tube socket connections due to age.
Intermittent resistors supplying B+ to the plates.
Intermittent cathode resistors.
Old capacitors.
Bad solder connections.

I could write a book.
Unless this amp has been recently and carefully serviced, have it done.

Yes, I had Bill Bickers rebuild the amp when I first got the jukebox a couple of years ago. He replaced the capacitors and any other failed components, checked the traces and reflowed as needed and set it up to take the non-Cobra cartridge. I have also checked it out and reflowed a couple of traces. Not to say there couldn't be an issue with a trace or some other component. As a clue to the root cause, the behavior is consistent. First it will get loud and distorted for a few seconds, then drop back to normal for the first couple of minutes of playing and then is fine for the rest of the time the jukebox is on. After several days, maybe a week, it will do it more frequently and for longer. This pattern continues where the loud bursts are more frequent, last longer and persist for a longer period of time until I say to heck with it, replace the tube and everything is fine again. Unless that points y'all to a specific issue, I'll just monitor it and see if it occurs with greater frequency.
Thanks
Brooks

Brooks,
My bet is on the tube socket--got some "Deoxit-5" ? Clean the socket with it and see if that helps --
Ron Rich

Yes, I've got Deoxit, so I'll give that a shot and see if the old tube works
Thanks

Ron Rich wrote:Brooks,
My bet is on the tube socket--got some "Deoxit-5" ? Clean the socket with it and see if that helps --
Ron Rich

I tend to "pinch" the socket connectors on tube equipment to make a better contact.
After decades of heating/cooling, the metal clips becomes "weak", plus it gives the tube a tighter hold.

MattTech wrote:

Ron Rich wrote:Brooks,
My bet is on the tube socket--got some "Deoxit-5" ? Clean the socket with it and see if that helps --
Ron Rich

I tend to "pinch" the socket connectors on tube equipment to make a better contact.
After decades of heating/cooling, the metal clips becomes "weak", plus it gives the tube a tighter hold.

Makes sense to me