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Well hello dere 813!

Andy Evans suggested a while back that I try the 813 in place of the 845, and since I had once bread boarded a 813 amp and liked the sound, I decided to try the 813 as a 26/813/813 low voltage amp. Operating points are just about the same as for the 845; plate volts about 430 vdc (same), plate current 68 mA (instead of 62 for the 845). The only real changes I had to make were to the cathode resistors, 390 ohms for the 813 vs 680 ohms for the 845. Of course the 813 is triode connected instead of being a true triode, but it sounds pretty good right out of the gate with a couple of NOS GE 813's I had on hand.
So this leaves me with some listening to do and some questions to ask.

First question
What is the difference in performance between a triode connected tube and a true triode likely to be? I mean it sounds pretty good to me, but it is no longer a true dht x 3 amp is it?

Second question
The operating points that Mike Lafevre posted of plate volts 430, plate current 62 mA and grid volts of -51 vdc from the Japanese dudes they claimed (and I tend to agree) are great for the 845; how did they come up with those? Is that most likely trial and error and experimentation, or is there a way they could have calculated that? I am wondering because the same operating points sound pretty good on the 813, but I would of course like to know if there are better ones. Looking at the plate curves, those points put you in a pretty linear region. I tried going up to 100 mA just for yucks and it did not sound as good to me. Each time I brought the current down it sounded better. I am a long way from being finished, but am wondering if there is an easier way than switching cathode resistors 50 ohms at a time.
Anyway this is going to keep me off the streets and out of mischief for quite a while as I will have to do a lot of listening and tweaking to both amps to determine which one I like the best. But hey, that's a good part of this hobby for me.

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Topic - Well hello dere 813! - vinnie2 17:43:42 10/16/16 (65)
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