My amp needs to see the doctor

ErikH

Well-known member
Just needin' to vent a little. :)

Friday night at practice my Marshall went down. It was fine a week ago, no signs of any troubles. She's been a workhorse for a good 16 years with a good amount of use. We were playing and we started smelling something. I go over and check my amp and sure enough that's where it's coming from. The power tube plates were glowing a bright orange (severly underbiased - don't know how) and then before I could shut it off, it shut itself off. No power, nothing. It has valve failure fuses but they're not blown. The mains fuse went though. I'm praying that the fuse blew before anything else but I'm fearing that one or both of the transformers went (Drake's too). :(

Pending what the local amp doctor tells me (I'm taking it in tomorrow), I'll either be getting it fixed or getting a new amp. As much as I'd love to get a new amp, and I have one decided on, I really want my Marshall up and running. It's been my main amp since the mid-90's. The previous owner used it a lot as well. It's seen some good gigging. That, and I don't have the funds for a new one just yet. Such wonderful timing, huh? :rolleyes:

I spent the rest of the evening playing through our keyboardist/guitarist's Peavey Bandit 112 (Sheffield speaker, Transtube technology). Not a bad sounding amp actually. He wasn't there otherwise we would've been done for the night. It was an audition night for a new bass player. Looks like I'll be mic'ing up my Lead 12 for the next few sessions. :6:
 
Re: My amp needs to see the doctor

What kinda Marshall was it?

Was it cranked a lot? It will be fine. Marshalls can be fixed so easy. Just go deal with your GAS
 
Re: My amp needs to see the doctor

OlinMusic said:
What kinda Marshall was it?

Was it cranked a lot? It will be fine. Marshalls can be fixed so easy. Just go deal with your GAS
My single channel JCM900 MkIII (1990 Model).

The MV was at around 4. The highest I ever had the MV was half way. I've seen the guts of it and it's pretty simple for a PCB based amp like that. Tube sockets are hardwired, PCB for the front controls, small PCB for the rear stuff.
 
Re: My amp needs to see the doctor

Rid said:
Aw that sucks:(
Hope that you will get it fixed.
Niels
That's the plan anyway. The tech that I've had service it before is really good. Too bad he moved his shop further away from my house. Now he's closer to my in-law's place...lol.
 
Re: My amp needs to see the doctor

Hehe...as the jokes goes.
The mum in law stands outside the house and knocks on the door, the son in law opens the door and looks at her being all soaked, mum in law mum in law why don't you go home???
It is raning cats and dogs;)
(sorry better in Danish)
Well all the best, hope that you did not fry the trafo!
 
Re: My amp needs to see the doctor

Rid said:
Hehe...as the jokes goes.
The mum in law stands outside the house and knocks on the door, the son in law opens the door and looks at her being all soaked, mum in law mum in law why don't you go home???
It is raning cats and dogs;)
(sorry better in Danish)
Well all the best, hope that you did not fry the trafo!
Thanks, me too. Those tranny's aren't cheap as we know.
 
Re: My amp needs to see the doctor

Anytime it's happened to me, it was usually a result of the bias being way off, and I ruined the tubes. The reason was the bias just drifted off on it's own, over time. I doubt you fried a tranny. You probably just need new power tubes, biased perfectly. Marshalls are a hard amp to destroy.
 
Re: My amp needs to see the doctor

That's good to know, Joe. I've just heard too many horror stories abour trannies going. That was the second thing that crossed my mind after seeing those tubes glow. Any brighter and they would've looking like a lantern element...lol.

Do you think the smell was from the tubes cooking? If that is the case, I'm thinking of trying some JJ EL34's this time around just for something different. Should the 12AX7's be replaced as well? They're about a year and a half old.
 
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Re: My amp needs to see the doctor

Erik,

Did you look inside of the chassis after the incident? Did you see anything burned, any marks or burned traces?

BTW, congrats for sticking with that amp. That doesn't happen allot. ;)
 
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Re: My amp needs to see the doctor

wixedmords said:
Erik,

Did you look inside of the chassis after the incident? Did you see anything burned, any marks or burned traces?
Nope. I don't go any further than taking the back panel off. The only time I've seen the innards is when it was last serviced. Me and high voltages don't get a long well. :)

wixedmords said:
BTW, congrats for sticking with that amp. That doesn't happen allot. ;)
I've had it for 10 years so I'm not about to just set it aside. It's my sound. But yeah, you're right. Some just write 'em off and get something else.
 
Re: My amp needs to see the doctor

Well, good luck with the tech Erik.

If it is either tranny, replacements can be had. Hang in there. She sounds like an old friend. ;)

Sending the lucky rabbits foot to ya. :)

EDIT: I know what you mean about voltage, BTW. Sure 110 volts is great Saturday night fun, but anything more rules out a "happy ending".
 
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Re: My amp needs to see the doctor

Sorry to hear they that a problem happened with your amp. On the topic of the pre-amp tubes I would probably just replace the phase inverter tube.
 
Re: My amp needs to see the doctor

Thanks for sharing my concern, guys.

Wixom, you are so right, she is an old friend. I've been told a few times to mod it. Bah, it's sounds great stock.

Greendy: I'll mention swapping the PI tube. Good idea. It probably took a good beating itself considering it's post MV.

You're a good man, Matt. I appreciate that.

I'll post an update tomorrow once I get word from the tech. Knowing him, he'll look at it while I'm there rather than having me wait a day to know for sure what happened.
 
Re: My amp needs to see the doctor

Best of luck Erik, hope it's a minor fix.... any chance the speaker cable may of been the trouble? My Marshall cabs jack loosens all the time and i have to watch it as a few times i found the cable just hanging there.... Plastic jacks do not belong on pro quality Tube Amps MARSHALL!!!!!!!!
 
Re: My amp needs to see the doctor

Hey, Chris. I check the speaker cable and it's snug as can be in the socket. No problems there. I wish he opened earlier than 10 AM sometimes but he's open until 6 PM so that's ok.
 
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