by bordonbert Sat Jun 17, 2017 7:55 am
Have you looked around in any other threads here Steve? There are loads that have this very discussion in them.
Valve rolling is genuinely mostly a waste of time if you are trying to make significant changes to your sound. Any differences you get with a different valve make are absolutely minimal particularly in comparison to speaker swaps. And any differences you get with a different valve type (12AT7/12AU7/12AY7) are because you have 'undesigned' the carefully designed stage and replaced it with another horrendously badly designed one which will have many unforeseen effects. The 12AX7/12AT7/12AY7/12AU7 'equivalents' are anything but that, they are totally different valves with every parameter vastly different! And, as it is widely acknowledged in the engineering arm of the music business, it is even impossible to evaluate the change between valves objectively given the time it takes to manually swap them over and run the amp up again. The only ways are to put the two configurations on a bench and measure things like frequency responses and transient responses and demonstrate the differences in those, or to have a single amp instantly switchable between valves by someone who does not tell you which valves you are listening to. Then you record a lot of your guess answers as you randomly switch between. The statistics show whether there is a REAL difference you can identify. Anything longer than just a couple of seconds during changeover and your ears recalibrate and you then hear what you want to hear. There is no 'golden ear' which can bypass this effect, we are all human and subject to psychoacoustics! (Anyway, the chances are you won't believe any of that so....
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Yes, the GM36 is widely acknowledged as being a toppy and strident and potentially harsh beast just in its underlying character. I genuinely feel it's designed that way and aimed towards the high gain metal market. I've been into its guts extensively in my time as an owner and it is a very very very complicated circuit configuration regarding its tone shaping, (unnecessarily so in many peoples' opinions), with the inevitable consequences that it can't be modified in any predictable way. The four channels are so intertwined with tone shaping switching options modifying each stage for each of the channels that you could improve one and ruin two of the others with almost any mod! It does what it does well well and what it does badly badly and you are stuck with that.
If you are using the DI then you are up against it here as any speaker changes will not be reflected in the signal to front of house, only local to the speaker cab. The only thing I can recommend you to try here is to swap your valves for 5751s. These are a genuine reasonable replacement for 12AX7s. Their characteristics and parameters are extremely close to the original 12AX7 with the exception that they have about 70% 'gain'. (that word gain is deliberately inside ' ' because there actually is no parameter of gain in a valves spec, there are a number of interdependent parameters which end up defining the gain of the stage but they change other factors of the stage alongside that, generally unfavourably and the real gain of the actual stage the valve is in does not drop by the same amount.) The 5751 is virtually a genuine 'low gain 12AX7' and can be dropped into stages designed for 12AX7s without any wild variation of the stages design remit. While they won't make a real difference tonally they will give you a bit more control of your gain at the expense of some of it at the extreme top end.
All that any of us can do is to get with it on that speaker choice as it is crucial in taming the upper stridency that creeps in. I swapped away from Vintage 30s myself as I found their sound ear slicingly painful. When I moved to a G12M filled Marshall 4x12 it improved very significantly. (Not even subtle, really like a different voicing in the amp, and that's in direct comparison when switching between the two instantly.) There are other recommendations to do the same thing but they are not speakers I am aware of and they would be somewhere in the archives. The search engine has once again refused to find ANYTHING for me no matter how or where I search so you would have to play about yourself to get this info! I do remember a particular Eminence driver as being proposed if you are in the USA.
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