Does anyone care to ask an amplifier designer a technical question? My door is open.

What causes a designer to choose a certain tube type for an audio circuit? Is the circuit designed around a specific tube, or is the best tube type found for the circuit that’s been/being designed? I know there are different electrical properties (I’m not an EE, so that is my untrained understanding), but does one choose the tube primarily for its electrical ability, sound, reliability, or some combination?

I know you would prefer that RM or RK answer this but I have something I can add. I asked this question of ARC's techs (I don't recall which one I spoke to) about their current penchant for designing power amps around the Tungsol KT150 and before that, the KT120. In ARC's case, I was told that they did the former-designed their amps around these tubes. If you happened to follow the history of the Ref series of amps, this is fairly obvious. The KT120 hit the market and the then-current Ref series of power amps were shipping with KT88's. They were able to handle the increased transformer demands presented by the KT120, but just barely. ARC reacted by beefing up their transformers to accommodate the KT120. Then the KT150 came out and this time, ARC was ahead of the curve rather than behind it-it seems they were got their hands on the KT150 before it was released to the public and were able to come to market with their Ref 75SE and Ref 150SE with KT150's installed. This was true of the GS "Galileo" Series as well. The tech I talked to told me that they felt the KT150 was far more linear and "accurate" than all of the predecessor power tubes, and also more durable. Too bad (for me) they are also significantly more expensive. That said, I used an ARC VS110 for about ten years and went through about six sets of various KT88's, 6550's, and even tried KT120's. I know, without a doubt, that I am getting far superior sound with my present amp, the Ref 150SE. The VS110 had a sweet slightly euphonious sound. Bass was good, but nowhere close to the solid slam I get with the Ref 150SE. The treble is far less grainy with my present amp as well.  

@fsonicsmith

Ralph-you should never have entered this thread. You tried to kill the OP with kindness and camaraderie, and he spit on you every chance he got. I think most of us reading through this thread can see the OP for what he is; entrenched in the remote past and bitter. His hubris is out of bounds. I have been around long enough to suspect that there must be something else going on in the OP’s life that is causing him to behave so poorly.

As Oldtech noted, this is my thread.

Hi,

fsonicsmith., you seem to troll my threads, this is not the first time I have encountered you. Aren’t you the one who said you knew only 1% of what designers know. I was looking for that one.. It appears a lot of your responses are now missing.

Ralph has not honored the stated purpose and rather come here to once again to hawk his paradigms and unusual ideas about cartridge loading and RFI.  You are into vinyl I see. Do you agree with his loading suggestons? Dont we load a cartridge to change its sound?  That last one about loading a cartridge for the sake of the preamp was so out of the world. Most of just a juse a ferrite bead to stop RF from coming in. 

I was happy to discuss his points till it got out of hand. Ralph can run his own thread if he wants to promote his paradigms. You write well, perhaps you could edit the one on Power so it makes some sense.

I do agree, Ralph should have never entered this thread nor should you. I dont see a question and I dont see a contribution. You left, said you wouldnt come back, but you did.

I dont mind any designer coming here if we both understand electrical science in its accepted current form and speak the proper language. If you want to read made up science there are pleanty of other threads on here for that.

I have a a question for Ralph, Why have you not sent an amplifier to Stereophile for review? They have reviewed all of mine and preamps too.

What prompted my question regarding tube types was the discussion in this thread about 6sn7/12au7/6sl7/5751/12ax7 tube type use for preamps and amp inputs. But there is also the question of power output tube choices - el34/6550/kt88/kt120/kt150, etc. It appears that some designers use the same tube types in their products, however there are instances where designers switch types year to year, or even have concurrent products performing the same function (amp or preamp) but using different tubes. Consumers and reviewers, also, sometimes prefer only 6sn7 or 12au7 based preamps, or kt120 or el34 amps, for example. I was hoping to get the viewpoint of someone who makes this choice. 

@ georgehifi
" I've set a 6sn7 in a preamp up on the oscilloscope and talked at it, and watched my voice being duplicated on the scope as wave forms superimposed on the 1khz test wave, and was quite eyebrow raising just how loud it was compared to the test wave."
Very interesting!
I would also amplify - lol - the sentiment that this is truly a wonderful thread!  :-)

Roger;
I have not deleted any of my posts. Not a one. 

fsonicsmith., you seem to troll my threads, this is not the first time I have encountered you.

I think you are mistaken. I don't recall ever entering into any debate of any kind let alone some type of trolling-skirmish with you. IMO, you are once again confused. 
Let me ask you this Roger; other than one of Ralph's amps, which modern era top-tier tube amps have you actually sat down and listened to with not just your own planar speakers, but also modern coned speakers across a decent spectrum? I ask because as I have said previously in this thread, you keep referencing ancient amplifiers of the remote past which you conveniently choose to piss all over. Others have asked you this same question too and you have not responded. Are you living in a cave?
I re-entered because I could not resist. I saw that your irascible behavior has continued and not just towards me, so I felt better about re-entering. I do respect you and your knowledge base, but it also pays to be a gentleman. Towards the end of his life, Charley Hansen (you misspelled his name a few posts ago-shame on you) was very vocal about MQA and his debate with JA on another forum became quite heated. Throughout that give and take, both managed to remain polite and civil. You could take a lesson from them. 
I brought up Charley Hansen's interview towards the end of his life about his latest iteration of amps finally-in his opinion-capturing the sound of the best modern tube amps. Have you sat down to listen to any of his amps? Have you analyzed why they might sound as they do from an engineering standpoint?
I am into vinyl, thank you. I am the proud owner of a Manley Steelhead, which I bought new. I love it and love Manley. I wish the aesthetics of their amps suited me more. I acknowledge that letting aesthetics get in the way of a purchase decision seems silly. I also acknowledge that Ralph's views on cartridge loading differ from my own. But as you quoted me (accurately), I have 1% of your engineering knowledge and his too. But I have years and years of empirical experience and based upon that, I have chosen to disregard Ralph's views on cartridge loading as simply not applicable to my particular system and experience.