One power tube socket is not sending power to tubes in my Mesa Express 5:50

[Freckles]

To clarify, I have already swapped and interchanged both power tubes and it seems that the left socket is the only one that fails to warm/light up the tubes. The amp powers up fine in spite of the fact that it's lacking all of it's edge with only one tube getting power. I know absolutely nothing about what could be the problem, and any suggestions would be well received.

[Enzo]

If one power tube socket will not light the tube heater, then either the tube socket is loose around the heater pins or the wiring is off somewhere, or perhaps cracked solder.

[Chuck H]

If it's the typical board mounted sockets that Mesa uses so often I would agree with Enzo and add that broken PCB pads or traces for the filament on that socket could also be the problem.

[jmaf]

If it's the typical board mounted sockets that Mesa uses so often I would agree with Enzo and add that broken PCB pads or traces for the filament on that socket could also be the problem.

I'm so prejudiced against PCB mounted sockets... In fact I take issue with a bunch of things Mesa does, but their marketing machine seems to run over us techies like a bulldozer, all I can do is bow and let them pass.

[g1]

In rare cases you can get a broken pin contact in a socket which will stay in place and look fine. But the connection at the tube pin will be open or intermittent. Pressure from your meter leads will make the connection read ok.
It's similar to a cracked lead on a component that is gooped to a circuit board, extremely frustrating to troubleshoot.

[Freckles]

All the responses have been more than helpful...especially considering the local guitar shop is telling me a month before anyone even gets around to looking at the poor thing. Is this an easy fix for somebody with knowledge of electronics? I'm contemplating picking my amp up and having a friend of mine take care of it. That is, considering the solution is relatively simple to remedy.

[g1]

Yes, someone with electronics knowledge could fix it. If they are not used to tube amps they need to read up on safety precautions regarding high voltage and draining the filter caps.
Then it is just a matter of finding out why the heater voltage is getting to one power tube socket and not the other. As others have mentioned the most likely cause is bad solder at the tube socket pins. With 6L6 type tubes the heater voltage will be approx. 6.3volts AC between pins 2 and 7.

[Freckles]

Thanks for all the help everyone. I decided to take it in to a local tech just because I was having a few other issues with the foot switch where the thing wouldn't power on unless the plug was sitting just right in the socket. I guess the downside of buying used gear is that it comes fully equipped with its share of wear and tear. All the help is much appreciated!

[Freckles]

Alright, a bit of an update for you guys....4 weeks later, and a few phone calls reminding the guys at my local shop that they still had my amp in the back room collecting dust...and apparently the techs there have given up on it. I called them for the third time this past Monday to check up on it and they said it still hadn't been looked at. Sometime within these short few days the techs at the shop had called Mesa, but hadn't gotten a call back and so they gave up working. I'm honestly at a loss...A friend of mine is an electrician, any chance he'd at least be able to tell me what the hell is wrong if he had a look, and given the insights pointed out in these posts?

[Chuck H]

IMHE "electrical" and "electronic" are different enough that your friend might be somewhat lost in an amp. When you say "apparently the techs there have given up on it" does that mean they looked at it and couldn't fix it? Because that's just lame and they have no right to charge you a dime if that's how it went down. And when you say "the techs at the shop had called Mesa, but hadn't gotten a call back and so they gave up working" does this mean that they don't feel they can proceed without information from Mesa? That's also lame and they have no right to charge you a dime if that's how it went down. Who did you take the amp to? I have no doubt that ninety percent of the posters here could diagnose that amp and most likely repair it. I've been hearing too many suspect repair shop stories lately. If they charged you for anything you were robbed. I think you should find another shop.

[Freckles]

You got it exactly right. They told me they had taken it apart, and apparently couldn't figure out what was wrong, so they called Mesa. They never got a response back from Mesa so then they called me just yesterday and told me that they were basically at a dead end and that the tech had stopped working on it. :/ The trouble is that I only know of one other possible tech in the area and from what I could find online most people didn't recommend the guy. I took it to the shop it's at now in hopes of avoiding a month long wait time and more hassles than I could handle, but that ended up happening anyway. Guitar Center is the next closest option that I know of, though I haven't done much research in my surrounding cities. I know my friend has experience setting up his own rig (guitars, amps, pedals, etc.) but I still have yet to ask him to take a look.

[Chuck H]

Where are you? I thought Whidbey island was the only place in the US that didn't have a good music electronics tech!?! Even in a pinch Whidbey's 70,000 demographic have access to Seattle for a two hour drive and a ferry ticket.

[Freckles]

I'm in Riverside, California so I'm sure I could find some other techs in surrounding county's. I'm in the Inland Empire, so L.A. is probably the safest bet. I've actually been thinking of calling Mesa myself and bringing it down to one of their locations out there in L.A.

[Enzo]

You have a tube socket that won;t power the heater. I can't imagine what Mesa could say to help. They will say the same thing we say - find the break in continuity between the sockets.

This isn't a conceptual problem, there is no concept for Mesa to explain that we are not getting. The two tubes are not powered in different manners. You would get the same advice from Fender or Peavey. FInd the break. Pull the tubes, and use an ohm meter. If these are 6L6 or EL34, then check from pin 2 on the one socket to pin 2 on the other one. Got continuity? Now measure from pin 7 on one to pin 7 on the other. Same question. If both have continuity, then I'd say the socket may be bad. If one of those two lacks continuity, then that is the problem and we track down just where the break is.

Imagine you have wall outlets on all four sides of your garage. (All on the same breaker) And ONE of those outlets is dead - no voltage. It is the same problem. And calling the power company or the company that made the outlets wouldn;t produce useful results. The problem is that somewher betwen the ones that work and the dead one, there is a break in the wiring.


And one hint. Heaters are usually wired socket to socket to socket. So if one socket appears dead, the problem may not be right at the socket. The wire going TO the previous socket worked, befcause that socket worked, but the piece of wire that LEAVES that socket to continue to the dead one might not be soldered well there. Might be soldered fine at the dead socket end, but isn;t getting any connecting where it came from.

[Jazz P Bass]

In rare cases you can get a broken pin contact in a socket which will stay in place and look fine. But the connection at the tube pin will be open or intermittent. Pressure from your meter leads will make the connection read ok.
It's similar to a cracked lead on a component that is gooped to a circuit board, extremely frustrating to troubleshoot.

Had one just like that on a Fender HR.
Cracked heater pin on a 12AX7.
It is always best to measure AT the pin itself.