300b vs 845

I concur, thanks to Phil for an excellent summary of his vastly greater valve experience than mine. i have just as it happens, installed the 845B valves in my Solista and am very impressed. I don't know if I would describe it as darker, but the base was the first thing I noticed. The amp audibly goes deeper and I believe the treble is better defined too and with better imaging too. i am tempted by the 845M valves, but I'm told they shine like searchlights and my wife is already muttering darkly about the heat from the Solista. I think anyone taking the plunge needs to take the greater heat with 845 based amps, into consideration, it really makes Summer use problematic.
Excuse me if I bang on about the Viva amps, but they are not as well known as they deserve to be. I believe a review by Art Dudley in Stereophile is imminent.

I meant to make it clearer that the Chinese graphite plate 845s, both the A and B, are darker sounding than the vintage NOS, KR and metal plate variants, which are in turn quite different from each other. If you've never heard anything other than the contemporary Chinese graphite plate 845s, then the 845B sounds as you describe, David. The 845M does light up a room, but I don't experience any more heat output than the 845B. It's just that the glow is more shrouded by the graphite plate configuration. They both get hot but if you've dealt with the heat issues for the B tube, the M will be no worse.

By all accounts the Viva 845 is excellent. I haven't heard it.

Phil

Guys, Thanks for the responses. I hadn't thought about the heat issue and that could be a problem the way I am set up. My problem my be my amp and not the 300b tube, I just don't have enough experience with SET.
Thanks
Mike

no heat issue really. the 845 845B and 845M all put out similar heat, and not as much as many. My monos use 4 of them, and the room is not hotter in any appreciable way. The 845M's are brighter (as in more lumens) than the 845 and 845B, but not hotter.

If the power supply design is correct and of adequate capacity heat should not be an issue with a correctly designed 300b. My Audio Note Conqueror was a space heater; my custom 300b tube rectified amp runs warm but does not materially impact the ambient temperature.