Amp lost its volume

[CJ]

Hey guys.. looking to confirm a problem on my amp. its a marshall 3203, so 12ax7 phase inverter, 2 power tubes, and solid state pre. After bringing my amp for a car ride, I now have a huge lack of volume from my amp. At about 2 or so the volume is normal, kinda loud, and then from there it doesn't really get much louder. Full volume is not all that loud. My immediate thought was that a power tube was bad and its running on half power. But they're both glowing, and I'm not sure if that's an indication of whether or not they're both working. I can't think of anything else it might be aside from the phase inverter.. but I honestly don't know what that is or how it functions.

Thanks fellas.

[JacksonRR]

If you're sure it's not the valves, check the effects loop solder job. I had one buddy who brought me his with a considerable volume drop and I found the effects loop soldering to be sub-par. Cold, dull, gray and cracking solder. Redid the joints and it was right as rain.

Anytime I have an amp problem I do a few things first before opening it up:

1. Try different leads, guitars
2. Make sure all settings are correct, front and back
3. Check pots for scratchiness or odd feeling, check jacks for loose feeling, dead battery for active pups etc
4. Plug straight into the effects loop's return, if it has one(see which half of the amp is the problem, preamp or power section)
5. Leave it alone for a bit as I'm too pissed by then to really be thinking about things
6. Find a schematic

Let us know what you find out. I'm OK at trouble shooting, but there's guys on here with TONS of knowledge. I'm sure it can be sorted out.  :D

[Frank]

Try plugging another preamp or any line level signal into the FX return, see if you can push the amp volume from that. If you can then the valve section is working ok and there's a problem with the preamp and it's off to the repair shop.

[hunter]

My first guess would be tubes. Indeed your Phase Inverter tube might degrade. Replace it with another (I guess it's a 12AX7 preamp tube). Or have the power tubes replaced. It's class A/B, so if one tube would fail in the power section, you wouldn't hear anything anymore. However they could just be losing their oomph.

Or something might have rattled lose inside the amp due to transport. Many reasons are possible. I would start with tubes.

[HTH AMPS]

My first guess would be tubes. Indeed your Phase Inverter tube might degrade. Replace it with another (I guess it's a 12AX7 preamp tube). Or have the power tubes replaced. It's class A/B, so if one tube would fail in the power section, you wouldn't hear anything anymore. However they could just be losing their oomph.

Or something might have rattled lose inside the amp due to transport. Many reasons are possible. I would start with tubes.

like Hunter says, valves are the likely culprit - try replacing the output valves first, then the PI valve.  Those are the two simplest things you can do.

in a push/pull amp (typical Marshall) you can remove one side of the output stage and (in the case of a 50w amp) have just one EL34 running and the amp will still work, not optimally by any means, but it will still work.

have you tried kicking it yet?    :lol:

[CJ]

I have not tried kicking it yet  :lol:

So wait, which is it? Hunter said one bad power tube would cause it to not work at all, but HTH you said it would. Or am I misunderstanding something? If it's as hunter said, then I don't think its the tubes simply loosing 'oomph', because it really only gets up to about loud talking levels. it probably lost 80-90% of its volume.

i'll try plugging into the effects return. and that also reminds me that i tried going straight into the amp, but forgot to disconnect my effects loop. i'll try both and see what happens. unfortunately my budget is super tight so i don't want to just start buying replacement tubes until i know its likely one thing or another

[Dmoney]

HTH has probably tried it. I didn't know you could do that.
The PI should have a much longer lifespan than the O/P valves.

I've had a 100watt amp loose a lot of output and it was down to a faulty output transformer.
I have had a 100watt amp running with 1 blown valve and when I got it second hand. I found it when checking the bias. No idea how long it had been running like that.

effects loop testing as described is the way to go to start with.

[HTH AMPS]

as has been advised - plugging directly into the effects send will give you an idea of whether its the output stage (big valves) or the preamp (small valves).

if the output has went THAT low, it does sound like the trademark shorted output transformer symptoms.

all that said, replacing valves is the best way forward - do you know anyone else locally with a valve amp? - could swap out the valves one at a time to narrow the problem down.

[CJ]

as has been advised - plugging directly into the effects send will give you an idea of whether its the output stage (big valves) or the preamp (small valves).

if the output has went THAT low, it does sound like the trademark shorted output transformer symptoms.

all that said, replacing valves is the best way forward - do you know anyone else locally with a valve amp? - could swap out the valves one at a time to narrow the problem down.

mother of god thank you. i had been busy all day and hadn't gotten a chance to look at my amp yet.. you scared the shite outta me  :lol: I unplugged the pedals that were running through my effects loop, and plugged my guitar in up front as usual. turned the amp to 2 and blew my ears off. huge relief.

so now i just need to figure out if it was one of the cables in my effects loop, something in the effects loop itself, or one of my pedals. i'm just happy it wasn't my amp. even if theres a problem with the loop, i can live with that for now

[HTH AMPS]

isolate EVERYTHING - its working now with no pedals in the loop.  now add one pedal, if it works add another - if it stops working at that point, its got to be one of the leads or the pedal (likely the leads).

[CJ]

well what's weird is the loop and pedals are still working. i have a pb&j, and a sonic stomp. both pedals still function through the loop. however as soon as i plugged them in, the volume dropped way down. i'll have to test the cables, pedals individually.

[JacksonRR]

Yeah, those amps really depress me for loop construction. Try using a lead that you know is good between the send and return, no pedals at all. This will test the loop itself. You said the pedals that you had in the loop were good, so it's either a bad lead or the loop is not making proper connection with a lead in one of the jacks.

Glad you are making some headway on the problem. When you treat your gear well and something goes wrong, it's usually the simple things that will eventually wear anyways: valves, leads, batteries, pots, switches and jacks. :D

[CJ]

well i just gave the whole amp a run through and cleaning of pots and jacks a few months ago.. so it likely isn't dirty. i'll try the single cable trick.. wasn't thinking i could do that. also i've resoldered the ends on each of my cables, so unless something happened, or i forgot one, it shouldn't be the leads. i'll check today

[CJ]

 :D Just a cable. One of the cables that I just resoldered the ends on appears to have a short from positive and negative, so theres the problem. I can't figure out where the short is though as both ends appear to be soldered well with the lead and ground well away from each other. oh well, maybe one of the 1/4" TS ends itself is no good. at least its not the amp  8)

[JacksonRR]

 :lol:Cables can make you think the worst sometimes. Glad it worked out.