Tube and Pot issues.

[danieldoyle]

Hi guys, just looking for some help with two of my amps! Sadly both amps have some issues and I'd really appreciate any advice you can give me.

So the first amp is an Ampeg Superrocket 212 Reverb/Tremolo, that I recently got in a trade. Disappointingly, when I receive the amp it wasn't working properly and I am not sure how to go about fixing it. So, very little to no sound is coming out of the speakers, regardless of the volume settings or channel selection/ All leads are connected and it powers on fine. Upon closer inspection I found that one of the preamp tubes is not lighting up and then in the power tube section, there are only 2 where there should be 4. I understand that removing 2 of the power tubes reduces the Wattage of the amp, but I wasn't pleased to find this as I wasn't informed prior to buying it. I haven't much experience with fixing tube amps, so what would be the best way to go about it? Would replacing the one preamp tube solve this problem or would it be better to go to a technician?

The second amp is a Marshall TSL 122 Combo. The amp works very well with only some minor problems. On the 3rd channel, the overdrive, when turning the Mid pot, the volume jumps, so there are a few points on the dial of Mid that double the volume, and other positions that keep the volume normal. This is only a small issue as I rarely use the overdrive channel, but means I can't customize the tone as I wish. Is this a problem with the pot or a greater problem that should be fixed now? The only other issues are small crackling sounds when the amp is idle, maybe the amp is in need of a revalve?

Thanks for any help in advance. Any further questions I can answer about the amps condition would be welcome!

[tedmich]

it could be as simple as replacing the preamp tube, likely the PI tube right before the power tubes, or the fuse which may be blown and keep to tube from turning on. I'd check all the fuses for continuity and then swap known good tubes in. The power tubes ARE lighting up? That's good as they are more expensive! Find a schematic for the amp (maybe here The Unofficial Ampeg Page) and be sure the fuses, where present are not blown. Past tube replacing you probably want to bring it to someone who knows these dinosaurs

The Marshall sounds like either a dirty,/bad pot or bad solder joint on the pot, you could try some fader lube/ pot cleaner spray available at radio Shack, and if that doesn't help you could check the solder and replace pot if bad.

[52 Bill]

I couldn't find a schematic for the super rocket so I don't know how that is wired, but try swapping the dead preamp tube with another one from the same amp. Does the same socket not light up or does the bad tube move to the other socket? Does the amp have an FX loop or a preamp out power amp in socket?

As for the Marshall, does the bad pot shaft seem looser than the others? It is possible that the pot has come apart on the inside of the amp. You could try and open up the amp and reassemble the pot and crimp the cover back on, if that's the problem.

[danieldoyle]

Hi guys, thanks for the replies!

I'm hoping it is simply just the preamp tube, but I can't be sure. I did swap the preamps and it was definitely the tube itself, not the socket, which is good. But if one preamp is gone, is it normal for the amp to be unusable? Hopefully there is nothing wrong with the socket, that might cause the preamp tubes to break. The amp was transported quite a distance to my home on rocky Irish roads, is it possible that the journey damaged the preamp? The power tubes are lighting up thankfully, is it safe to continue running the amp without the other 2 power amps, so long as the preamp tubes are functional? Or would it be better to put the full 4 in? The ampeg has a line in and a line out also! Here's the manual for the Ampeg, if that helps: http://www.ampeg.com/pdf/SR212RT.pdf

As far as the Marshall is concerned, hopefully it is only a bad pot and nothing more serious. I will have a look at the pot when I get a chance, but I wouldn't be fully confident in my abilities to fix it! As I said, the problem isn't too bad and I can deal with it, I would hate to cause more damage trying to fix it!

Thank you both for the help so far!

[soundguruman]

Hi guys, just looking for some help with two of my amps! Sadly both amps have some issues and I'd really appreciate any advice you can give me.


The second amp is a Marshall TSL 122 Combo. The amp works very well with only some minor problems. On the 3rd channel, the overdrive, when turning the Mid pot, the volume jumps, so there are a few points on the dial of Mid that double the volume, and other positions that keep the volume normal. This is only a small issue as I rarely use the overdrive channel, but means I can't customize the tone as I wish. Is this a problem with the pot or a greater problem that should be fixed now? The only other issues are small crackling sounds when the amp is idle, maybe the amp is in need of a revalve?

Thanks for any help in advance. Any further questions I can answer about the amps condition would be welcome!

You should clean the controls and jacks with the proper type cleaner like caig deoxit d 100 and the proper lube like caig fader lube...
using the wrong type of cleaner can destroy the controls and jacks.
You have to spray the cleaner inside the controls or jacks and rotate the control several times.
sounds like mid control is dirty but it "could" be broken, or the solder joint may be bad. Clean first, and test again.