Musicians Roadhouse

Just a question if anyone has any ideas on this. I have a JCM 600 head that I’ve had since new when I was in the UK, brought it to Canada with me and converted it to 110v (with Marshall's assistance at the time, they provided me with the drawings, transformer mod information and the replacement neon switch). It has two channels, Serial and Parallel loop and spring reverb with separate controls for each channel. I have not used it for quite a while and fired it up last weekend. What I found was there is a lot of noise (hiss) from the amp. I have been using the DSL-1 50th Anniversary mostly so the noise of the JCM600 was more apparent. I could not recall it being this noisy before. What I did discover is if I turn the reverbs off (down to 0) it goes a lot more quieter. Just wonder if anyone has any thoughts on this. Is it common for Spring reverb units to have noise? Worth repairing or can it even be repaired? Or should I just stick a reverb pedal in the loop and forget about the spring? I know this was not a popular amp and was only in production for a couple of years only. Thanks. Dave

Humm, you might be hearing more hiss because the dsl1 is a much lower output.
I would check all of the connections to the reverb tank first