Welcome back to my blog. One of my buddies for whom I’ve repaired several amps by now, both solid-state and tube, brought me a small Marshall Valvestate 10 amp. Like the other amps he brought, this one seemed to have been stored in somebody’s outdoor shed for ten years.
When I plugged in the amp and powered it up, it was dead. Nothing, nada. Before opening it up, did a quick inspection to ensure there was not LCM (Loose Conductive Material) in the inputs, that the pots were not outright shorting out, and that the switch was opening/closing contacts as it should.
I then proceeded to the rear, and did a quick check of the speaker and wiring, hoping the speaker wasn’t blown (ie speaker cone separated from the transducer, etc.)
At this point, I had to open the amp. Now I love working on Marshalls because they are a technician’s dream to work on, having service options considered in the design.
Like the Marshall Reverb 75 I worked on for the same dude, removing the top 4 screws on the cabinet frees the amp section for easy removal. The amp is of open chassis type, which is very convenient, once you’ve moved the green ground lug terminal allowing for the PCB (Printed Circuit Board) to be removed.
I could see nothing obvious or out of the ordinary such as charring, or broken components (ie dried/burnt resistors or electrolytic caps). But I did notice the AC input fuse was open. I also noticed that the current fuse had already been replaced, but with one of a greater value than specified. IMPORTANT NOTE: Never replace a fuse by one with a higher rating. For example, a 250mA-rated fuse should never be replaced by one rated 500mA or 750mA. Never replace a specified fuse of 1A by one of 1.25A. Over rating fuses can be hazardous for fire and defeats the purpose of protecting the circuitry intended to be protected by the fuse. In other words, the electronics may actually become the fuse for the fuse, if you know what I mean.
I replaced the fuse with the correct one, put all pot controls to 0, then powered up the amp. Red LED indicator ok. On. I waited a half hour
This amp has been around for almost ever. You can see an old thread of folks here from over ten years ago asking about this amp here.