Not a typo. A brain fart. Thanks for the correction. I am still learning my tubes. Been a solid state guy for a long, long time.
Bascom King stepping in here - I didn't see the misquote yet but indeed the BHK Signature 250 amp is to shipped with Genelex Gold Lion 6922 tubes. As a matter of interest, perhaps someome can tell me how to respond to a particular post. I haven't seen any obvious way to reply to them so I tried this.Welcome to the forum, Bascom! You can add your input to a thread by clicking on Add Reply at the bottom of the page, or respond to a specific post (as I'm doing in this case) with the Quote button at the upper right of a specific post. Then your post will include the quote you are responding to as you can see above.
Hi audio.bill:
I am taking Paulās advice by clicking on the URL link in the email message that I get from someone. This way, it goes directly to the post in the forum and allows me to respond right then and there. Kind of neat I will try the other ways and get better at thisQ
BHK
Elk said +1Hey, Elk, BHK working on my forum chops - Yes a lightly driven and even a hard driven triode can be very linear. Especially if it's load line is made horizontal on the volt/amp characteristic curves. This is made possible operationally by a circuit called a mu follower. That means the tube has a gain of it's mu value and the device added to make this possible provides a low output impedance. Dan Wright used this technique in some of his products which I have had several coming up to my present OPPO 105 modified by Dan. I'll tell you, those Sophia 6SN7 tubes in that circuit does sound extremely musical! However, as in the BHK Signature 250 amp, a pair of triodes in a differential amp configuration that is degenerated to a low value of gain is very linear with the even harmonics cancelled and sounds great too. The bottom line is that a well configured dual triode differential amp followed by appropriate MOSFET circuitry can produce killer sound. The New PS Audio preamp will also be a variation of this theme.A simple typo.
My understanding is that a lightly driven triode is very linear. If correct, this may be part of the magic.
What intrigues me is that Paul is not seduced by euphonic tube sound. I am certain the amp is not coloring the sound in any fashion whatsoever. Thus, what does a tube do in the context of this amp that solid state does not?
(I have been gently tempted to buy one of the plug-in SS replacements for a tube just to play with it. But aesthetically I just could not due it.)
Thank you!
I am extremely eager to hear the new amp. 
BHK said Hi audio.bill:I am taking Paulās advice by clicking on the URL link in the email message that I get from someone. This way, it goes directly to the post in the forum and allows me to respond right then and there. Kind of neat I will try the other ways and get better at thisQ
BHK
Go Bascom!!
Welcome Bascom! This reminds me of the DIY-audio-fix-it forums of the past few years where Nelson Pass would make a surprise appearance and talk about and answer questions regarding his designs. A great opportunity for all!
Iām glad you mentioned the 6SN7 tube, what an unsung hero! From the 50s/60s this tube is a real workhorse. With its macho-sized glass envelope and generous-sized elements it is a quiet and linear pre-amp performer when backed up by a capable circuit! These were a favorite and often found in old TV sets of yesteryear but later on audio designers realized this tubeās much greater potential. Cheap and reliable back thenā¦now considered suave and sophisticated in some of the best sounding tube mono-amp designs of today.
Your use of triode tubes in a differential configuration in the BHK Signature 250 front end sounds very intriguing indeed because of how it affects the tubes natural output tendencies in most circuits! It seems that vacuum tubes are famous for generating lots of even order (ear-pleasing) harmonics and this tends to make things sound better but not necessarily more accurate. By using the differential design you are essentially eliminating (or damping significantly) this natural tendency of the tube. Can you comment on how effective this is and does it enable cancellation of the āevensā to the -90 to -100 db range? What about the more objectionable āoddā order harmonics that are left behind? The ear is less enthralled by them. Since you are cancelling the more pleasing harmonics what about the residual oddsā¦much lower in amplitude perhaps but are they still a consideration for your circuit design? Logically could they be even more of a concern since the evens are gone and can no longer mask them!
Iām not sure you answered Elks question regarding what a tube can do differently or what tubes may contribute to a circuit that may be different than what a solid state component will. But perhaps you would revisit itā¦because it is a great question. I have owned Krell, McIntosh, Levinson, Audio Research, Conrad Johnson and many othersā¦all sound different. But what I have found is that with tubes there is (at least for my ears) an ability to somehow bring out, extract, capture or otherwise convey a scintilla more of what I call ārealismā that is just difficult to hear and seems to be missing when I listen to SS circuits. My explanation is simplistic and not very scientific, but there you have it.
Thanks for sharing your thoughts in this forum!
Hi straylight:
Yes, a differential connection of the input dual triode will tend to cancel the even harmonics in each output phase but no where near the -90 to -100 dB range. The input stage is differential by necessity for accepting both balanced and unbalanced inputs and both output phases are needed to drive the output amplifiers which produce the separate two output phases, the difference driving the speaker load. So even harmonics are reduced by the differential input stage and the final difference across the load. That said, we are left with odd harmonic distortion products, the third being dominant. These come both from the input and output stages. What I find interesting is that this amplifier doesnāt sound dissonant or irritating despite all of the historical amount of information that odd harmonic distortion is said to be sonically bad. It is amazingly truthful to the music.
BHK
Thank you, Straylight! Excellent, interesting post.
And welcome!
What are the ratings of the amp transformer?
Do you mean the power transformer or the output transformer? Just kidding! Actually there are two power transformers. One for the output stages and the other for the tube front end and auxilliary functions. When you say ratings are you talking about the power rating of the output stage transformer or the volt and amp ratings of itās windings?
BHK
Hi, Bascom.
I am thinking primarily of the current rating or how much power it can deliver in a āworst caseā scenario.
I have seen transformers in the 2KVA region on such high power amps, and since PS Audio is very observant on the power supply capacity I would expect something similar.
Thanks
Frode
Hi Frode:
Well not exactly similar. The KVA rating of the output stage power transformer is, according to Bob Stadtherr, Chief engineer at PS Audio, 1 kVA. It is more than sufficient to deliver the goods. Of course, a pair of BHK Signature 300ās, from the perspective of power transformer capability, would be twice as much.
BHK
Bascom,
Thanks for your response on the earlier circuit design question. The 3rd order harmonic is indeed a very low order harmonic, so if 3rd order is the predominant one this would potentially be the least objectionable compared with higher order types and therefore would give rise to excellent sound.
Have another question on the design of BHK Signatures. With so many MOSFET devices in the output stage (16 per channel for stereo amp and 32! per channel for the BHK 300 mono amp) how important is MOSFET matching for sonic performance and circuit stability? Do you spend allot of time matching MOSFETS? Also how do you manage/dispense with all that MOSFET thermal energy buildup and keep it all stable.
My experience is that some of the best sounding solid state amp designs Iāve heard are not necessarily the ones with the most output devices. Perhaps fewer components with better quality matching (curve tracing) is at least as important. Do you feel there is a trade-off implicit when balancing circuit simplicity vs. sheer number of outputs (current capability). How have you approached balancing this design criterion?
thanks.
Which tube is the BHK being voiced for? Iām under the impression Iāll have to get my own set of matched tubes (say from Upscale Audio http://www.upscaleaudio.com/6922/ ) as Iām sure PSAudio wonāt have the time to buy matched pairs, but which tube will be the one used for voicing? And which would be recommended for best bang-for-the-buck? Or cost-is-no-object?
Thanks so much.
āSSW
Paul McGowan said We're supplying it with matched Gold Lion 6922Oh! That's a new development. Is that what was used for voicing?
So I donāt need to get my own matched set, then?
āSSW
Streets Still Works said Which tube is the BHK being voiced for? I'm under the impression I'll have to get my own set of matched tubes (say from Upscale Audio http://www.upscaleaudio.com/6922/ ) as I'm sure PSAudio won't have the time to buy matched pairs, but which tube will be the one used for voicing? And which would be recommended for best bang-for-the-buck? Or cost-is-no-object?Thanks so much.
āSSW
Not wanting to endorse any specific tube supplier, there is a guy that lives at the base of Mt. Baldy in CA that is the real deal, if you get my drift. I have visited him and he set me up with some very nice Mullard military stock CV4004/12AX7s and CV4024/12AT7s. I see that if someone wants to try all the types of 6922 tubes, it would run about $5k for pairs. For $8 per tube he will provide them cryo-ed. I am sure the Golden Lions are excellent, and it is great that there is some decent new production out of Russia. But sometimes the vintage stuff is so nice. I am sure there will be plenty of opinions on tubes as the amps get put in service!
That would be Upscale Audio, the link I provided above.
The big question is that if the amp was voiced to the Gold Lion (not too āsparklyā per Kevin at https://www.youtube.com/watch?v=P9UP1SopdTE&feature=player_embedded), what happens to the sound when another vintage tube is used?
Seems like if one sticks to the Gold Lion and replaces them often enough it should be quite sufficient.
Hmm, but that leads to another question: How often should they be replaced? I made myself a tube hour meter so I can monitor tube hours. But are these 4000 hour tubes? 1000?
Oh, and lest I forget, I have also bought my preamp tubes from TCTubes.com
Streets Still Works saidMy guess would be in the 3,000 to 10,000 hour range. I think that is typical with most designs using ECC81/ECC82/ECC83, so I would imagine the 6922s would be in the ballpark. I have never used a tube up but I am working on it. Some will say NOS tubes last longer (and sound better) just due to better metallurgy, better care in production, whatever. To my ears, tubes of different make and vintage do sound quite different, and so far I have found a least one NOS vintage tube of every type I use that knocks the socks off current production stuff, but even Kevin will tell you the current production tube are often excellent and you don't need to go with the expense of NOS if you are not obsessed (big qualifier there!). Tube rolling can be very fun, but very addictive and very expensive if you let it be.Hmm, but that leads to another question: How often should they be replaced? I made myself a tube hour meter so I can monitor tube hours. But are these 4000 hour tubes? 1000?
How does your tube hour meter work? My ātube hour meterā is the timer on iPhone along with a spreadsheet!
socal77 said
How does your tube hour meter work? My "tube hour meter" is the timer on iPhone along with a spreadsheet!The tube hour meter is one I got from Jameco and wired it up with 4 mono mini jacks and a reset button in the small case. It's powered by the 5VDC trigger so it runs whenever the amp is on. It's a nice little timer. Here it is as compared with a quarter:
Damn I want one of these puppies Now! - Iāll have to go with the stereo version to keep costs down. (I do wish there were a power supply upgrade to get some of the benefits of the monoās - down the road)
Has anyone heard back about getting one of the pre-release units? I put in a request though Mayoura since she is who I usually deal with but havenāt heard back. Iām glad I waited and didnāt jump on one of the Pass .8 series, (which also would have been a great choice) Iām using an old (but tweaked) Spectral DMA-50 for now (on my TAD CR1ās) which works quite well with an Atma-sphere tube preamp. The tubes pre gives it the density, real sounding tone and dynamics and the SS amp controls the speakers and resolves quite well. The best combo Iāve had on the system and better than all SS. I am however using a very unusual set of speaker cables which are non metallic and present the highs in a very relaxed way, since the speakers and amp are a bit forward in nature. I am assuming I will have to re-cable the entire system to get the right balance with the BHKās.
Can you contact me instead by email? Mayouraās not been with the company for many months now.