Trouble shooting my amp

[frtbzz]

I've noticed that when I approach 7 on the master volume on my amp its starts compressing more, like its working too hard or something, almost like I'm losing volume. When I pass 7 its starts farting out and cutting out the harder I pick. When I get to 8 and beyond it just gets worse and does it all the time. It cuts out and farts/flutters out. I've never noticed this before since I never had it past 6. When I play at lower volumes(5 or under) it doesn't do this. The thing is I can't play at 5 because its not loud enough standing beside my drummer.
Its hard to explain in words what it sounds like without actually hearing it.
Could this be a PPIMV problem?
Thanks Chris.
Its a '79 Marshall JMP 50 watt MV with a PPIMV. Its not just the bass farting out either. Its much more pronounced than that. A heavy swirling,oscillating, farting sound. Totally unplayable past 7.

 

[TimmyPage]

Re: Trouble shooting my amp

What amp do you own?

 

[frtbzz]

Re: Trouble shooting my amp

'79 Marshall JMP 50 watt MV with a PPIMV.

 

[joelap]

Re: Trouble shooting my amp

You might get more of a response here or here: www.hoffmanamps.com or www.metroamp.com. Those are two forums for amp building, the metroamp one specifically vintage marshalls. Not sure if you checked there, but worth a shot maybe? Sorry I cant help, I cant get the B+ right on my amp :smack:

all the best.

 

[frtbzz]

Re: Trouble shooting my amp

Thanks Joe. I just joined Hoffman amps and posted there too.

 

[sosomething]

Re: Trouble shooting my amp

Tubes biased too hot = not enough headroom?

That'd be my first guess.

 

[frtbzz]

Re: Trouble shooting my amp

I have them at about 68% to 70% max dissapation.

 

[danglybanger]

Re: Trouble shooting my amp

trouble shooting my amp

...work on your aim maybe? :laugh2:

sorry. couldn't resist

 

[kmcguitars]

Re: Trouble shooting my amp

The 1st place I'd look is the PPIMV. I would meter both pots. Gain&PPIMV to see if there working to spec. Could be a bad wiper on the pot or dirt and oxidation. The guys at Hoffmanamps are more knowledgeable,But the Guys at Metroamps (Mainly George) know Marshall's inside out, especially with a PPIMV... It's there specialty.

 

[sosomething]

Re: Trouble shooting my amp

I have them at about 68% to 70% max dissapation.

Well then nnnnnnever mind! I've hit the limit of my expertise.

 

[bungalowbill]

Re: Trouble shooting my amp

Filter caps?