Mod 50 power drop

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destratification

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I turned on my mod 50 for the first time in a while (it's been on stand down since axefxII and behind m4 rig duties) and played for a spell when the power just dropped suddenly (like 90-95%).

I suspected tube failure but just from a visual, it looks like the power tubes are still glowing normally. I haven't begun tube swapping - but I have a spair pair of 6550s I'll try. If it's not the power tubes, which preamp tubes would be most likely to fail and which should I begin swapping out. I haven't come across a preamp tube reference/map - is there one somwhere?

I did a search in the forum and came across the send/receive deox method...I'll also try that.

thanks for any info!
 
I don't know the Mod 50, but I wouldn't think the preamp tubes would do this. If it isn't the power tubes, I would think more like power transformer or fuse. Have you checked the simple stuff- cables and whatnot?
 
I've had the power drop after a power tube blew on my MOD50 but the warning light came on. Your not seeing the led light up? The dirty serial loop jack thing sounds more like cutting in and out with crackling.
 
Definitely check/clean the loop jacks. If they're dirty they can manifest in a few ways.
 
Thanks for the replies everyone. I did a bit of troubleshooting last night but didn't make any progress.

Here's what I've done:

Checked cables, just guitar > input (no pedals)

Removed reverb tank from parallel loop

Inserted cable into serial loop and in and out a few times (no effect)

Swapped modules, clicking through all channels with no effect. Except that now channel 1 of my Salvation dual matchvox now makes no noise whatsoever. That module has been problematic since I got it back originally and even after I returned it for repair (that's another story and frustrating). Could faulty circuitry in a module cause any issues with the circuitry in the amp head?

Replaced power tubes with 6550s, biased, checked the fuses (these are used and I can't guarantee condition, but they are glowing and no red failure light).

Replaced all the preamp tubes (again, these are used and I can't guarantee condition, but they were working when taken out of my modules when I swapped for tone shaping tube experimentation). I found the tube layout online. When I replaced the phase inverter tube it seemed to make a very marginal difference in volume - I could have been hearing things by then.

It's still about 90-95% shy of original volume and there is a slight bit of distortion/crackling.

Not sure what else to try before having to send it to a tech...
 
One more "simple stuff" suggestion: The power cable. I don't know the Mod 50, but if it is removable make sure it is fully seated. Try another one if you can. Try another wall socket also- one that is on a different line if you can.
 
If you must ship it to get repaired, you can send it to me.
 
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