benadrian wrote: Sun Oct 02, 2022 6:54 pm

Owen wrote: Sun Oct 02, 2022 6:38 pm Mesa 400+

Play 1/4 of our set, all of sudden it drops about 10% volume (no crackle, no problem sounds), we stop, turn up volume and turn it back to where it was and it is back to normal. Play another 20 min everything totally fine. Start the set again, and the volume drops again, do the same thing and it is fine for 10 min and it happens again, after this time, it is stable for the rest of practice.

What do you think, bad power tube?

If it's one of the 12 power tube versions then one power tube going bad would not lose that much volume. Hell, I bet you could pull one power tube at random and not really be able to hear a difference.

What's happening is that something is causing the signal to drop somewhere in the circuit. Could be a preamp tube, a solder joint, a component, some node of the power suply, etc. But it's probably something well before where the signa splits to hit all the power tubes in parallel.

FIrst thing I'd do is test all the tubes. Then I'd run the line out and/or effects send into another amp or interface and try to get the amp to fail. Basically, any available output will tell you something. An excellent scenario would be to take a send from the effects send, the slave out, the balanced out, and then mic the speaker cab and plug it all into an interface and record all four channels at the same time

Then, when the amp fails and is in the failure state, you can see at what points the problem shows up. I don't know the 400+ circuit by memory, but my guess is that the FX loop is in the middle of the preamp, the slave is at the end of the preamp, and the balanced out could be pretty much anywhere. Since the failure happens at the speaker cabinet, you know it has to be the speaker cable or earlier. However, if the effects loop out does NOT lose level when the speaker loses level, then you know the problem has to be in between the effects loop and the speaker jack.

In short, chop the amp up in to sections and find out which sections break and which do not break

Owen wrote: Sun Oct 02, 2022 7:15 pm I don't have a tube tester, so I guess my next steps will be to run the line out into one of my other amps and see if I get it to fail and try each output. Just try to get as much info as I can before I bring it to my tech.

tommy wrote: Mon Oct 03, 2022 9:11 am

Owen wrote: Sun Oct 02, 2022 7:15 pm I don't have a tube tester, so I guess my next steps will be to run the line out into one of my other amps and see if I get it to fail and try each output. Just try to get as much info as I can before I bring it to my tech.

Before taking it to a tech I'd do the following:

1) Try replacing the preamp tubes one at a time with a known good one.
2) check to make sure that the volume drop happens at different places where the master volume is.
3) reseating every power tube isn't a bad idea if the problem is intermittent.

I forget how the 400+ inputs are set up. Does 2 cascade into 1 like the D180? If not, it's not one of those pots. If they do, it could be the one that's active with both inputs.

tommy wrote: Mon Oct 03, 2022 9:11 am

Owen wrote: Sun Oct 02, 2022 7:15 pm I don't have a tube tester, so I guess my next steps will be to run the line out into one of my other amps and see if I get it to fail and try each output. Just try to get as much info as I can before I bring it to my tech.

Before taking it to a tech I'd do the following:

1) Try replacing the preamp tubes one at a time with a known good one.
2) check to make sure that the volume drop happens at different places where the master volume is.
3) reseating every power tube isn't a bad idea if the problem is intermittent.

I forget how the 400+ inputs are set up. Does 2 cascade into 1 like the D180? If not, it's not one of those pots. If they do, it could be the one that's active with both inputs.

Kniferide wrote: Sat Oct 01, 2022 1:58 pm anyone know of a tap/die set that I can rework mic stands and clips with? I have a ton of old stands and clips that could be saves if I had something but Tap sets are crazy expensive and I only need the one size

Kniferide wrote: Tue Oct 04, 2022 2:20 pm

Kniferide wrote: Sat Oct 01, 2022 1:58 pm anyone know of a tap/die set that I can rework mic stands and clips with? I have a ton of old stands and clips that could be saves if I had something but Tap sets are crazy expensive and I only need the one size

found this on amazon and ordered. Figured if I can save some old stands, why not.

https://www.amazon.com/27-Right-hand-Th ... B008B1VTY6

twelvepoint wrote: Tue Oct 04, 2022 2:54 pm

Kniferide wrote: Tue Oct 04, 2022 2:20 pm

Kniferide wrote: Sat Oct 01, 2022 1:58 pm anyone know of a tap/die set that I can rework mic stands and clips with? I have a ton of old stands and clips that could be saves if I had something but Tap sets are crazy expensive and I only need the one size

found this on amazon and ordered. Figured if I can save some old stands, why not.

https://www.amazon.com/27-Right-hand-Th ... B008B1VTY6

If the threads are stripped, of course a die won't bring metal back, so I imagine your plan is to hack off the stripped part and cut thread onto what is now unthreaded?

Kniferide wrote: Tue Oct 04, 2022 3:08 pm

twelvepoint wrote: Tue Oct 04, 2022 2:54 pm

Kniferide wrote: Tue Oct 04, 2022 2:20 pm

found this on amazon and ordered. Figured if I can save some old stands, why not.

https://www.amazon.com/27-Right-hand-Th ... B008B1VTY6

If the threads are stripped, of course a die won't bring metal back, so I imagine your plan is to hack off the stripped part and cut thread onto what is now unthreaded?

On most of the stands I have the same problem, they have been banged around and shit for over a decade and it s really hard to get the threads just right to screw them into a clip without cross threading. hoping this can carefully recut the threads enough to help with that. Also, not against using it on some copper pipe or something to make custom stereo bars and shit. Dunno. seemed worth having around.