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

@ 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. 

@krelldreams 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.

Thanks for an on point question. For years Everything ARC made used 6550s. Some makers are similarly fond of EL-34s. Some consumers are in love with that little 9 pin EL84.

Part of the tube choice is driven by, you, the consumer. I built an EL84 amp because I know there a lot of people who love that tube. I did do someting different and got 35 watts per pair rather than 17 watts. I raised the power, kept the safety and life of the tube and made somethig to this day people do not believe possible. The application is laid out in my 2018 Burning Amp presentation.

On the other hand I built the RM-9 to take any octal power tube, of which there are many. Power stays the same, only the negative bias changes. I did this so that users could compare widely different power tubes on the same platform. In my thinking how can someone say something general about a particular power tube when they are comparing it in two different amps? David Manley got very upset over the RM-9 and we exchanged several letters in pubic in the Stereophile. They are fondly known as the Manley/Modjeski letters. I hope to get them up on the HIFI school site. At the same time we coined the term "Tube Rolling" and I made buttons imprinted "Member, Nimble Tube Roller Society" This was way back in 1983 so young folks may have missed it. David was totally opposed to tube rolling.

You can take an old RM-9 and use 4 of the KT 120s or 150s instead of 8 of the earlier tubes. Will still produce full power with half as many tubes.

What I see in the market place now is that New Sensor (Tungsol) is creating larger power tubes and there are those designers who appear to get out a new amp with the new tube as fast as they can, which does worry a bit. If a designer goes for the full power of a KT-150 and you have to go back to the 120 or 88 you will loose power. If the Russians do something bad the KT 120 and 150 could disappear until someone else takes it up. You can add your own "ifs" to the list. HP and other equipment makers had a policy any part had to have at least one other supplier. Single source parts not allowed.

Tube cost is another criterion. EL84s are very inexpensive, EL 34s next. then 6550/KT88, KT 120s. However the KT150 cost to me is about twice the KT 120. The look and power are quite a departure and I will not be surprised it the next bigger KT is already in the works.

KT, stands for Kinkless Tetrode in the UK. We use Beam Power Tube in the USA for the 6550 which is essentially the same thing. The first beam tube was the 6L6, a great tube that no one uses because the public has someting against it, for no good reason.

In essence, You, the buyer are controlling the tube choice as much or more than the designer. Hope you choose well. :)

I read both links. The first is common knowledge and nothing about RF. The second is long so if there is something in particular you want to me to read please quote it here. Are we playing "Wack A Mole’ here?

Im really tired of RF being the devil for everything. Usually if there is RF sensitivity you will hear an AM radio station. If there aint no radio coming in there aint no RF. Lets get real please.

For the What’s Best forum, just look at JCarr’s posts. No whack a mole- not even sure what that comment is even supposed to mean.

No-one has said RF is the devil for everything except you, just right now. But these two links did point at RFI (or ultrasonic or near ultrasonics, in the case of MM cartridges) being a problem with LOMC cartridge operation... I don’t see how that can be construed as ’everything’.

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.

This statement is outlandish and false. Please note though that I am not attacking you, just the veracity of this statement, unlike you who sees fit to attack me personally. I have honored the stated purpose, as I am a designer of amps and my door is open.

If you say you looked at both links and came away with the idea that RFI has nothing to do with it, the only conclusion that can be drawn is that you didn’t in fact read the links or failed to comprehend their significance. When we are talking about noise in the MHz range, that’s RFI, especially when it is the result of excitation of a tank circuit.

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.

Roger, you seem to appreciate my being courteous when I offer corrections (which you seem unwilling to accept), but you seem unwilling to be civil in return.


Contrary to yours and others impressions, this is not your thread- its a public forum.


As a bit of a hint, I find that keeping decorum in spite of personal attacks (including outright untruths) is a simple tool to maintain credibility. FWIW I have an EE just like you and I don’t engage in pseudo science any more than you. I can prove everything I say. I suspect that you are not *as* acquainted with equipment from the old days- 1960s and before, as I might be. You have said that my talk about the Power Paradigm and the Voltage Paradigm is the pseudo science to which you refer; to me that just suggests that you don’t have a grounding in history. This despite my showing an example of what I was talking about (one that we have discussed prior); in spite of that evidence (the Fisher A-55 I linked, and any amplifier with a ’damping’ control) right in front of your face, yet you still accuse me of pseudo science!


But:
You are getting out of hand here. This entire thread is in violation of Audiogon posting rules, for the simple fact that you primarily use it for promotion.
On occasion I get accused of the very same thing, but those that do so will note that I have yet to start a single thread on this site (despite being active on it since its inception in the 1990s), let alone one that focuses primarily how great I am in tandem with how great my products are, all the while demeaning (in some cases, falsely) others. I do mention my products when asked and also in the context of related questions (such as balanced operation; quite often because there is much misunderstanding about how balanced lines are supposed to work).

This is not your thread! - if that were the case it would be on your website. Instead you are posting on a forum that is open to the public. My presence here has mostly been to keep the record straight when things have gone off the rails. The 6SN7 thing and the cartridge thing are two examples.

I can see that it bothers you as much as it does me when you see things that are untrue. If I can offer a bit of advice:We often go thru live with made up stories. In fact we live as if those stories are true. When life and the stories don’t agree we suffer. At that point, to end the suffering the best thing to do is drop the made up story. You will note that I do not attack the voltage rules as being made up. I regard them as an engineering solution, but one that has some bad applications. I’ve pointed out why earlier and don’t need to repeat myself. The old power rules are one way out of the resulting colorations of the voltage rules, but they come with their own price (limited market, for one, more fiddling and more careful equipment matching for another).


IOW, if you think I made up the idea of the power rules, you are simply not grounded in history.


I am perfectly happy to have that conversation on a different thread. I’ve been having this conversation for the better part of 30 years and its not been debunked by any engineer that listens- only those who don’t and are further unaware of how the voltage rules were developed.

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.

I got my degree at the UofM. I don’t subscribe to anything made up. Enough with the innuendo already- if you don’t get what I’m talking about, just say so, otherwise lay off. John Curl got it, Nelson Pass got it, other engineers on this site got it...

Regarding Stereophile:
We sent a preamp to TAS for review. It did quite well- the reviewer bought it and said so in the review. Then he moved over to Stereophile prior to the publication of the review; it got published there. At that point we knew we were in trouble when we got the news that he had jumped ship to Stereophile, as we had been warned by people from several companies (ARC among them) that if you can’t afford advertising with them, they will treat you as a sacrificial lamb to show how hard hitting their reporting is. Sure enough, some months after the initial review was printed (in which I had to challenge JA’s measurement comments, as the Audio Precision at that time didn’t properly support a balanced input, despite it appearing so- a different conversation), and after being asked if we would advertise in the magazine, the reviewer was later instructed by Stereophile editors to print a followup. Apparently when he was installing defecting tubes in the preamp, it didn’t work right. We tested several of those tubes; one was a Telefunken that was so dead that I thought my tester was at fault as it got no reading at all when the Telefunken was lit up. I had to test some known good tubes to know that I was not going nuts! To date I’ve yet to see another 12AT7 that bad that still had a vacuum. We got blamed in the followup for that failing on the part of the preamp. Do you have amps and preamps that function correctly on bad tubes?

A second product, the MA-2, was destined for a nice review in 2004 by Paul Bolin when he was with Stereophile, but a company that was trying to take over my company threatened Stereophile with a lawsuit if they didn’t give the amp back to them. Paul let me know this was happening, and since we owned that amp I went and picked it up. While the lawsuit never went down, JA was sufficiently rattled by that event that he removed Paul from the Stereophile staff.

Regarding the issue of cartridge loading, in a past thread here Jonathan Carr (Lyra cartridge designer, who I believe has also designed some phono stages) stated as follows:

I should now debunk another myth regarding loading, which is that low-impedance MC cartridges are insensitive to capacitive loading. OK, the MC cartridges themselves aren’t particularly sensitive to capacitance, but the inductance of the cartridge coils will resonate with the distributed capacitance of the coils and the capacitance of the tonearm cable to create a high-frequency spike, and this spike certainly is sensitive to capacitance. In general, the less the capacitance the better. Having more capacitance (across the plus and minus cartridge outputs) will increase the magnitude of the high-frequency spike and lower its frequency, neither of which is good news for phono stage stability or phase response.

Generally speaking, the greater the capacitance across the plus and minus cartridge outputs, the heavier the resistive loading needs to be to control the resulting high-frequency spike. Conversely, less capacitance allows the resistive load on the cartridge to be reduced, which will benefit dynamic range, resolution and transient impact.

The relevance of the Hagerman link Ralph provided in his previous post is that it illustrates the high frequency resonant peak (i.e., the "spike") formed by the interaction of the inductance of the cartridge and the load capacitance that it sees.

I am not in a position to say whether or not the **only** relevance of resistive loading of a low output moving coil cartridge is to control that peak, and its potential effects on the particular phono stage. However I certainly wouldn’t consider the possibility that it could often at the very least be an important factor in the performance of a system to be "out of the world," as Roger stated.

Also, while I don’t recall the exact numbers, Ralph has stated in some past threads that he has observed remarkably high levels of energy emanating from LOMC cartridges at ultrasonic or RF frequencies.

Also, FWIW, I’ll mention that Keith Herron, whose company and products (especially his phono stage) are about as non-controversial and highly regarded as they come, suggests that with his particular phono stage no loading whatsoever will often be found to be preferable with LOMCs, regardless of the cartridge type. (The LOMC input of his phono stage is FET-based, and it applies a load resistance to the cartridge that is nearly infinite when load resistors are not connected externally, to RCA jacks that are provided for that purpose). And I have found that to be the case in my own system, with an AT-ART9 cartridge having a recommended load of "100 ohms minimum."

Finally, without placing blame (although I have my own thoughts about that) I’ll just say that it’s a shame that an otherwise wonderful thread is compromised by the fact that two long-time designers of highly regarded audio electronics can’t deal with each other in a more respectful and matter-of-fact manner.

Regards,
-- Al