Marshall Jcm

Marshall Jcm

What would you like to ask?My Marshall JCM 900 100W Hi Gain Dual Reverb TUBE half stack amp broke....?

So My Marshall JCM 900 100W Hi Gain Dual Reverb TUBE half stack amp broke. What happen is that I turned the STANDBY and Power on at the same time all the time and one day it turned off and than it shut right off and now it won't turn back on. Its been broken for a few months. Can someone please tell me how to fix it, or where to fix it, and how much it would roughly cost. Thank you.

I doubt if turning on both switches at the same time caused your problem. The standby switch allows the the power tubes to idle but otherwise be ready to go since they remain warmed up when the power switch is left on.

Try replacing the fuse(s) first. Make sure that the replacement are the exact type and rating for each. Don't be tempted to use the wrong size or wrap them in tinfoil. There job is to limit damage to the circuitry if a tube wears out or something else goes wrong. If the replacement fuse also blows, stop. Your amp requires the services of someone who is familiar with tube amps and has the proper test equipment.

Most likely you'll need new power tubes and possibly a bias voltage/quiescent current adjustment if your amp has one. Other failures that I've seen include power supply problems, and tube sockets and output transformers that have arced over and shorted out when the amp was run without a speaker and the power had no place else to go.

Your cost to repair could be anywhere from the cost of a few fuses to a few hundred dollars if there was a major meltdown.

Don

Marshall DSL 100 amp 1/2, JCM 2000

Marshall Jcm

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