I have a marshall 100w JCM 2000, DSL 100 Head, going into a 1960 A 4x12 cabinet. Which inputs and settings should i use on the rear of the amp in order not to damage it

I would suspect a bad cable. Also, these symptoms show up if you mistakenly use a speaker cable (unsheided) as a guitar cable (shielded).

Please see my other answer.

It sounds like you have a dead guitar cable or the preamp section of the amp is blown. It needs to go to the shop. It's way cheaper in the long run to just take an amp in. If you try poking around without knowing what you're doing you can fry something more expensive or worse yet yourself! There are leathal voltages in a guitar amp!

the second jack is usually for a second cabinet.



http://www.marshallamps.com/downloads/files/MG100%20hbk%20Eng.pdf



here's a link to the manual. to be sure.

if it has effects on it, you may require two cabinets for the stereo effects. in the truest sense of stereo is what i mean.

IF YOU ARE USING THE LEFT INPUT OF THE AMP PLUG IT IN ON THE LEFT INPUT OF THE 212. RETURN AND SEND.

if this a tube amp then your tubes might be going bad. but if it is a solid state amp then im not to sure whats going on.

Very nice amp!

First off, is the amp getting sufficient power? An unreliable AC current from your wall can affect the performance.

Have you tried the amp with a different speaker? Checked for a loose connection from the amp to the speaker? Is it the correct ohms rating?

Second, are you experienced in electronics? The problem could lie in a faulty solder connection, a bad component, etc.

If you are not confident in opening the amp and troubleshooting it yourself, take it to a audio repairman. Marshall's are some of the easier ones to fix.....

Since you are getting some output, the amp section is probably OK. There are circuits designed to handle thge difference impedence outputs. This should be a relatively simple repair for any shop that handles these units. If you don't have one local to you, let me know and I'll locate the service info and get you more specifics.

Dan

There is a bridge rectifier and red and black wires jumping from preamp tube to preamp tube. These need to be resoldered, take it to your favorite pro audio service center. I'm doing this to the same amp right this minute! Send it to me, I'll fix it. Tom Peary Norman's Electronics Atlanta, Ga 770 451 5057 www.neiusa.com