Preamp tubes not glowing & no sound!!

[ThatMarshallGuy]

My Marshall JMP 2203 that I ordered came in today and after firing it up for the first time, there was no sound........at all. I looked inside and the power tubes are working fine but the preamp tubes are not lit up at all.... What could this mean?? I would really appreciate a quick replay as I'm really trying to figure this out quick. Thanks.

 

[Frankie]

Pull the preamp tubes out, leave it on standby, plug them in one by one and see if they light. That'll rule out a short in a tube. After that it sounds like a heater wire could've come loose.

Edit - Is the a US model JMP?

 

[ThatMarshallGuy]

Is that safe to do? Turning the amp on without preamp tubes in it then putting them in ?

 

[ThatMarshallGuy]

Yes it is a US Model JMP

 

[Jaymz E]

Some pre tubes don't light up good, even if they are new. Electro Harmonix 12AX7s don't light up well because of the spiral filament design. Do you have any extra 12AX7s to try out? Good Luck, I'm sure one of the resident techs will chime in and help you out.

 

[ampmadscientist]

Frankie seems to be right.
The filament wire has a bad connection somewhere(?)
You will see the preamp tubes light up, or you should see it.

 

[Frankie]

Yes, it's safe to do as long as the amp is on standby. Turn off all the lights in the room to really make sure you're not getting heat. And Jaymz is right, some preamp tubes don't light well, but if you're not seeing any heat for sure you won't get any sound. They don't work cold. I had a heater wire come loose on my 1987 during a show and barely squeezed by based on the heat already in the head box. The amp was sounding pretty weak by the end of the set.

If you have a known working preamp tube, really any 12 type like a 12AU7 or a 12AT7 would work, pop that in with the amp on standby and see if it lights. If it doesn't then you might have a loose heater wire. Heat runs from the power tubes to the preamp tubes in order, so if you lose V3's heat you'll lose V2 and V1 also.

 

[ThatMarshallGuy]

Yes, it's safe to do as long as the amp is on standby. Turn off all the lights in the room to really make sure you're not getting heat. And Jaymz is right, some preamp tubes don't light well, but if you're not seeing any heat for sure you won't get any sound. They don't work cold. I had a heater wire come loose on my 1987 during a show and barely squeezed by based on the heat already in the head box. The amp was sounding pretty weak by the end of the set.

If you have a known working preamp tube, really any 12 type like a 12AU7 or a 12AT7 would work, pop that in with the amp on standby and see if it lights. If it doesn't then you might have a loose heater wire. Heat runs from the power tubes to the preamp tubes in order, so if you lose V3's heat you'll lose V2 and V1 also.

Okay. If I took it into a tech to have this wire looked at, how much would it cost to have it fixed?

 

[Frankie]

I couldn't tell you; that's something I'd normally fix myself. I'd imagine just whatever their bench fee is though. If it's just a loose heater wire it's a really quick fix.

 

[Frankie]

The red and black twisted wires at the very top of this photo are the heater feeds. See how they're all hooked together? Mine came loose at V3 and took V2 and V1 with it. Took longer to get the chassis out of the head box than it did to solder that connection.

 

[ampmadscientist]

I couldn't tell you; that's something I'd normally fix myself. I'd imagine just whatever their bench fee is though. If it's just a loose heater wire it's a really quick fix.

Seems like the bad connection is on the power tube socket closest to the phase inverter.
It's not unusual for that to happen.

 

[ThatMarshallGuy]

Seems like the bad connection is on the power tube socket closest to the phase inverter.
It's not unusual for that to happen.

All power tubes are on and glow though. So how could that be?

 

[ThatMarshallGuy]

Okay so I unplugged all the tubes and put them back in.....I don't know what was happening before but the amp works now. Who knows. Anyway, thanks for all the info guys.

 

[CRobbins]

Okay so I unplugged all the tubes and put them back in.....I don't know what was happening before but the amp works now. Who knows. Anyway, thanks for all the info guys.

Probably just a loose nut behind the guitar.

 

[Frankie]

To the OP: It sounds like you might just have dirty tube sockets. Get some contact cleaner (there's nothing better than DeOxit), spray it on an old preamp tube's pins, then work the tube in and out of the socket 3 times. Repeat for the other sockets.

The power tubes could easily glow while the preamp tubes wouldn't. Like I said the heater lines start at the power tubes and then run to the preamp tubes. Seems pretty common that the lines come loose right after the last power tube, leaving the V1-V3 without heat.

 

[CRobbins]

All kidding aside, Frankie is probably right. I'm glad you got your new amp working.

 

[ThatMarshallGuy]

To the OP: It sounds like you might just have dirty tube sockets. Get some contact cleaner (there's nothing better than DeOxit), spray it on an old preamp tube's pins, then work the tube in and out of the socket 3 times. Repeat for the other sockets.

The power tubes could easily glow while the preamp tubes wouldn't. Like I said the heater lines start at the power tubes and then run to the preamp tubes. Seems pretty common that the lines come loose right after the last power tube, leaving the V1-V3 without heat.

Yea that's probably it because everything works now. I'll clean it out when I get new tubes.

 

[ThatMarshallGuy]

I'll be posting a new thread soon with pictures of this great amp so keep your eyes peeled!

 

[Frankie]

Well... how's it sound?! I'm dying to know.

 

[ThatMarshallGuy]

Well... how's it sound?! I'm dying to know.

Fantastic!! Really aggressive and crunchy!! This is my first tube amp!