Quote:
Originally Posted by golgi 
I've got some spare Mullard CV131 tubes for my ld2+ sitting around. I see that this one of the type of tubes that can be used on the MKIII. Have any of you tried these out yet? If so then how do the compare to the stock tubes? Thanks.
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The CV131 is a variant in the EF92-family of tubes. Compared to the EF95 tubes that come stock with the MkIII, the EF92 draws a bit more current (200mA for EF92 versus 175mA for EF95) and therefore has more gain and runs hotter (the heat shouldn't be a concern on the MkIII, though). In theory, the EF92 should have a more linear top-end response owning to its higher gain and my personal experience has been that, when compared to each other, the best EF92 I've tried has a sweeter treble while the best EF95 I've tried has more authoritative bass. That said, there are more factors besides tube families that can affect how tubes sound, such as manufacturer, variants within the same family, and vintage, just to name a few factors. The sound of the amp does vary quite a bit with different selection of tubes (which is a feature of tube amps, I believe), and it's up to the individual audiophile to try out different types of tubes to find the best combination for yourself.
Keep in mind especially that since the pre-amp out on the MkIII is directly powered by the driver tubes only, your selection of driver tubes will affect the quality of your pre-amp output in a significant way.