Amplifier distortion help please

Hope someone can help. I seem to be having a weird problem, in that I keep getting distortion on the left channel of my system. This does not happen all the time, but usually, once it starts, the amp is damaged. It occurs from either of my two turntables or my Cd player.

So far I have had my Musical Fidelity 'The Preamp' in for repair, one of my Sugden P128 monobloc's, and now the amp I bought for a spare whilst the Sugden is in for repair, a Marantz PM-54 is distorting on the left channel. I also tried a friends DPA power amp and this distorts too!

Most of the time I have been using a pair of aged Mission770's, but changed to my spare pair of Celestion DL12's and left channel is distorting, although this was after it started distorting with the Missions.

Talking of the missions, the smaller coil on the crossover board looks like it used to be connected to the negative speaker wire post, but the wires stop just short of this on both crossovers.

Added later: Yesterday I turned on my system and left channel was distorting badly with very low volume being produced. I changed the left speaker and it then sounded fine. Replaced with original speaker and still sounded fine - ie no distortion ?????????

Here's hoping,

Counting backwards Speaker -> speaker wire -> amp -> interconnect wire -> preamp if any -> interconnect wire -> source.
Check each interconnect and speaker wire for solid termination first. What termination you're using on your speaker wire? Check bananas firm onto socket and for solid termination or cut bananas away and use naked wire(best termination is no termination at all)
I betcha both of your speakers had lived quite a life and need a fair amount of TLC or replacement if you realy want to stop frying your amps.
Thanks for the reply. Speaker wire is connected bare without banana's at speaker. Bare into amp via monster cable reducers.
Would be odd if all three source components were causing problems. Why would older speakers be an issue? And why does the problem come and go please?
Speaker is the load to your amp and speaker components tend to go old especially the voice coil, looses flexibility, expands so much that it's in friction with magnet just like joints that may catch later on arthritis. Depending on stress it may or may not contract or expand free.
Old speakers need re-work and re-work on old speakers with limited possibility to get correct crossover and driver parts may be very challenging. It can be done easier if you will use outboard electronic crossover but even that having in mind, you may end up finding better complete speaker for the project price. You've mentioned yourself that it'll be odd about all three source components and that's where you've found the answer to your own question. Now ask the same question about both of amps... The fact that you've fried already amp once is evident that speaker voice coil failed to contract/expand once and will do it again and probably more frequent sucking out your budget for replacement pair.
Furthermore I'd advise you not to connect to your rig any of your current speakers at this particular moment. You can get any low-priced floor-standing JBL, Polk or Klipsch from Best Buy and return it within a month to see if your components will expose the same intermittent problem.

Hope I found the best and diagnosed at my best your intermittent problem.
Have you checked to make sure your wall outlets are wired properly? You can buy inexpensive testers at Home Depot etc....
Thanks again Marakanetz I borrowed another amp and all is fine, guess the missions were the problem(I hope!).