And then there was one: second amp has failed

Clockworkmike

Clockworkmike

Ambassador of STACKS in WV SHACKS
Country flag
Well, I lost my JCM900 SLX a while back and never got around to getting it repaired when I should have. But, I didn't play it much and still had my main one working fine ( JCM2000 DSL50) along with the Mode Four. But in a cruel ironic twist of fate, it died today

Why is it ironic? Well, I have been away dealing with issues and getting things taken care of one by one and had been making some good progress. I find it's easier to just deal with one problem at a time and move to the next one instead of trying to take on a bunch of stuff at once. So, knocking out some stuff that was going on, I was thinking " well hell, stuff is getting better!" And after not having ANY desire to play a guitar, I picked it back up about a week ago and got a bit inspired to play again. But today after playing for about a whopping 5 minutes? My amp just slowly faded in volume until there was nothing coming out of it.

I changed my cables, I changed my guitar, I plugged it into the FX return to see if I could at least see if the power amp was working but nope, zilch. The amp lights up, the tubes are glowing but very dimly and I have nothing but silence. So now, I have no choice but to send it off and see what happens. I guess the other one that was dead alongside it will go too. My luck? Probably end up more in repairs than the cost of finding one used to just replace it altogether, but I hope im wrong. I hope I'm dead wrong actually.

Just my great luck
 
Far Rider said:
We're just born under a bad sign Mike. It sounds like your power supply has given up the ghost. @T-Rex might be able to give you better info.
Click to expand...
Eh, it's gotta get better sometime though right? Whenever that is lol

But yeah, that's kinda my suspicions as well: output transformer went bye bye. I have no way of proving this or knowing it, but I gotta feeling
 
Clockworkmike said:
Well, I lost my JCM900 SLX a while back and never got around to getting it repaired when I should have. But, I didn't play it much and still had my main one working fine ( JCM2000 DSL50) along with the Mode Four. But in a cruel ironic twist of fate, it died today

Why is it ironic? Well, I have been away dealing with issues and getting things taken care of one by one and had been making some good progress. I find it's easier to just deal with one problem at a time and move to the next one instead of trying to take on a bunch of stuff at once. So, knocking out some stuff that was going on, I was thinking " well hell, stuff is getting better!" And after not having ANY desire to play a guitar, I picked it back up about a week ago and got a bit inspired to play again. But today after playing for about a whopping 5 minutes? My amp just slowly faded in volume until there was nothing coming out of it.

I changed my cables, I changed my guitar, I plugged it into the FX return to see if I could at least see if the power amp was working but nope, zilch. The amp lights up, the tubes are glowing but very dimly and I have nothing but silence. So now, I have no choice but to send it off and see what happens. I guess the other one that was dead alongside it will go too. My luck? Probably end up more in repairs than the cost of finding one used to just replace it altogether, but I hope im wrong. I hope I'm dead wrong actually.

Just my great luck
Click to expand...
Do you want to try and troubleshoot it?

You need a volt meter; and my I advise you: this is a two-beer problem. You'll need enough beer to make it through.
But if you want help, I can walk you thru.
 
DirtySteve said:
I would grab a known good 12ax7 and swap it in each position one at a time to see if it's a preamp tube. It won't hurt anything to try and it's an easy test.
Click to expand...
Amp Mad Scientist said:
Do you want to try and troubleshoot it?

You need a volt meter; and my I advise you: this is a two-beer problem. You'll need enough beer to make it through.
But if you want help, I can walk you thru.
Click to expand...
CoyotesGator said:
What do the preamp tubes look like?

Phase inverter tube passed?
Click to expand...
I'm fairly certain I got about 3 12ax7s lying in my drawer, still in their boxes. This is worth a chance, hell, might as well try it. I'll check in the morning and see.

@ampmadscientist , I have my meter in my truck and sure, if you want to give some pointers? I'll listen.
 
67plexi said:
The Phase inverter tube fail would cause no sound V-3

Use this voltage chart

View attachment 99336
Click to expand...
Hey, thanks! That's a start to go try! I'm gonna mess with it here in a little while, roll some tubes around and I'll check the voltages.

Those tubes have been in there for probably 3-4 years. Before kinda just not playing at all, I'd typically play thru the amp anywhere from 3-6hrs a week, so not a lot by a real musician's standard but enough time to definitely age and wear them down.

Those were those Shuguang Silver Dragon 12AX7s and I won't be using anything that cheap again to be honest. There was this whole craze going on about them being these aggressive gain monsters but, I never saw it but rather just some cheap Chinese junk to be honest lol
 
My two cents.

On my Traynor, while it didn’t go dead quiet…. Some years back I did lose a lot of gain. Probably 1/2 power. As I’d had the amp forever and had never done a re-tube. I decided it would be a good day to do that. And as luck would have it. It fixed. Don’t know which tube failed, and frankly didn’t concern me. And since I’ve never really played thru it that much and when I do/did I tend to play at lower volumes….. I just figured the tube(s) died from old age and not abuse.
 
Clockworkmike said:
I'm fairly certain I got about 3 12ax7s lying in my drawer, still in their boxes. This is worth a chance, hell, might as well try it. I'll check in the morning and see.

@ampmadscientist , I have my meter in my truck and sure, if you want to give some pointers? I'll listen.
Click to expand...
Did you check the HT fuse?
Plug a short guitar cable from effects send to effects return and test it again.
Try swapping out preamp tubes.

If that doesn't turn up anything, you can start checking the power supplies.
There is a DC power supply for the preamp tubes, and I would suspect that first.

Pull the first preamp tube out (closest to the input jack)
Set meter for DC volts.
Connect the red probe to pin 5 of the preamp tube socket.
Connect the black probe to pin 9 of the preamp tube socket.

Turn the power on but, do not turn standby on.
Leave the standby in "warm up" position, and do not turn standby to "operate" position.
Now you should see 6 volt DC at the preamp tube socket...pins 5 and 9.

Then if you don't see the 6 volts at the preamp socket, the DC filament supply needs to be repaired.

If you do see 6 volts DC at the preamp tube socket, then let's check more voltages.
Cause one of them has died, probably.

Changing the output tubes: not yet. Check more of the voltages first.
 
Clockworkmike said:
Well, I lost my JCM900 SLX a while back and never got around to getting it repaired when I should have. But, I didn't play it much and still had my main one working fine ( JCM2000 DSL50) along with the Mode Four. But in a cruel ironic twist of fate, it died today

Why is it ironic? Well, I have been away dealing with issues and getting things taken care of one by one and had been making some good progress. I find it's easier to just deal with one problem at a time and move to the next one instead of trying to take on a bunch of stuff at once. So, knocking out some stuff that was going on, I was thinking " well hell, stuff is getting better!" And after not having ANY desire to play a guitar, I picked it back up about a week ago and got a bit inspired to play again. But today after playing for about a whopping 5 minutes? My amp just slowly faded in volume until there was nothing coming out of it.

I changed my cables, I changed my guitar, I plugged it into the FX return to see if I could at least see if the power amp was working but nope, zilch. The amp lights up, the tubes are glowing but very dimly and I have nothing but silence. So now, I have no choice but to send it off and see what happens. I guess the other one that was dead alongside it will go too. My luck? Probably end up more in repairs than the cost of finding one used to just replace it altogether, but I hope im wrong. I hope I'm dead wrong actually.

Just my great luck
Click to expand...
Do you know about BR3 issue on SLX's amps?
It's a 1A bridge rectifier that it's installed so close to PCB board. It suply voltage DC heater to V1, V2 and V3. Take a look on It. Also you need replace C8.

It's a issue that have all SL-X amps. V1,V2 and V3 use 900mA from BR3. BR3 gets so hot and fails. Volume drops.

Could be phase inverter tube as 67plexi said. Phase inverter is V4.
 

Attachments

Last edited:
Mike: I was just thinking about you and your recent Blues. And here you are with a new thread!

If it’s not an obvious problem with the PI or power tubes, pull all the tubes and check and note the voltages. Without the load from the tubes, the voltages should be higher than normal by about 10% roughly. Take note of the incoming AC voltage too.
 
Appreciate the help fellas!

So this morning, I did the obvious thing first and checked fuses. HT fuse is popped. So, the problem arises here first but the question is, is this common that they just randomly blow or am I looking to something bigger? Unfortunately, a fuse like this (T500mA) isn't something i can get anywhere local, so at a minimum, I gotta order some, in which Ill order some mains fuses as precautionIMG_20240505_113720150_copy_918x1632.jpg
 
You must log in or register to reply here.
Back
Top