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Question: Is it the preamp valve going off?


JPJ
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As some on here will know, I own what is probably the heaviest amp known to man but despite my advancing years and failing back, I cannot find anything lighter that provides the sheer depth of this thing - my beloved SWR SM1500.

However, on the last couple of gigs, I've noticed that the mid range seems to ebb and flow over the course of the gig. To explain, I start off with a nice bit of mid grind in the tone and at certain times this seems, to me at least, to disappear to be replaced by a lot more bottom end. I've emailed SWR's helpful customer services (3 times, no reply) so I'm putting it out to you guys for your help and guidance. Could this be a sign that the pre amp valve is reaching the end of its natural life?

Back in the days of my slightly lighter SWR750X I upgraded the stock GT12AX7 valve to an EH5751on the advice of a Basschat user who published a really in depth comparison of preamp valves on here (sorry I cant remember who it was :blush: ). The change on that occasion gave me a bit more mid-dirt (which I liked). Do you think its worth doing the same thing with the SM1500 or should I just replace like-for-like?

Help, advice and guidance will be greatly received B)

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What you describe doesn't sound like a failing valve to me.... could it be your ears playing tricks on you as they get "tired" during the gig?

The easiest thing to do is swap the valve out for another of the same spec and see what happens, and you can always try other brands as well without risking anything. Whenever I have owned an amp with valves in I have always enjoyed seeing how different brands affect the tone.

Edited by walbassist
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