KR 2A3 + NOS 5AR4 = Puppy Love! (so far!)

[Erik Mandaville]

All:

Ed mentioned he had tried the KR 2A3s, and suggested I give them a try. We are both using the very good Sovtek output tubes, but I have always been interested in the KR. That tube had remained in a cost-prohibitive class, however, and this was just such a great opportunity to see what they might sound like. I've heard so many mixed reactions on them (the KRs), that one can never really be sure of one's impression (of anything!)until one has the opportunity to audition whatever that thing might be...at least so I believe!

...and if that last sentance makes any dang sense at all, I'm glad!

Without getting into all the techno-mumbo-jumbo (God, that gets boring after awhile!), the KRs benefit from a slightly higher calorie diet (volts!), and so I opted to try them with a good NOS 5AR4 rectifier. This would provide a bit more oomph than the GZ37s that had occupied that spot in the amps before. In this way I could supply a reasonable amount of extra power without having to bypass the primary dropping resistor in the power supply (which would probably add once more the difference between the 5AR4 and GZ37)

At any rate! I let the amps warm up, and spent some time cleaning the listening room of dust (gets everywhere!), and put in a selection of wind concertos by the Baroque composer, Telemann. One added not before my initial listening impression: With the AES AE-1 preamp (purchased from Edster), 25 of interconnect, and the KR/5AR4 combination, the system is quieter than it has been; I mean, almost nothing in terms of background noise, hum, buzz, etc.

After an hour of listening, the main thing I have noticed is excellent high frequency transient response, stronger grip on lower frequency info (in this case beautiful sounding cello), and violins that have a really fine silkiness -- with great resonance of wood and rosin! Fabulous! The main thing that struck me were woodwinds, though....an honestly very pronounced wooden quality that I hadn't been so aware of before.

More to come, but I'm just really enjoying the listening. I may just have to start digging into my piggy bank! Before that, though, a new CD player has to be the next audio-related expense!

Erik

[kev313]

Good review Erik. Please let us know more as you continue with these this tube. I was interested in it for a time, but Kelly's comments so thoroughly scared me out of my shorts that I hadn't considered it for a while. Thanks for your input.

[Erik Mandaville]

Kev:

I'll tell you thing I know about Kelly H. that I know for sure: He has considerable experience with many different tubes, and is able to speak with authority on the subjective differences between them in different applications. He is also not alone in his perception of the KR 2A3 as a bit of a disappointment for the investment. I have heard and read the same from many very knowledgeable tube 'folks.' Even Vacuum Tube Valley's report on the KR was kind of lack-luster.

The KR tube may just happen to provide a sound; a sonic signature; a musical character trait -- whatever one might want to call it, that I have so far liked very much. Ron W. always sort of strongly hinted at (ahem)his rather firm belief that KR tubes will provide so-inclined-listeners with an extra sense of clarity and detail. In my case ('cause my high frequency hearing isn't as good as it used to be), this expensive 2A3 brought some things out in my system I hadn't been so aware of previously. Only time will tell if it's something I'm honestly hearing or just the result of human psychology -- meaning, it's new, so it has to sound better. I don't think that's the case, though.

In any event, I'm just the sort of person who will try something for myself in order to get the most accurate idea of whatever that might be. Leok recently suggested something I agree with whole-heartedly: that choices in tubes is a highly subjective matter. That's the really neat thing about this!

I've got to stop this writing and go and listen!

Erik

[Deang]

Everything related to this hobby is subjective: Tubes, caps, wire, resistors, source components, front end circuit types -- and on and on it goes.

As far as the KR tubes go -- I feel they are the only current production tubes that have old world quality.

Now, when I hear someone say that 'xyz' product has 'no soul' -- it's generally an indication to me that it's probably something I should check out. Yeah, 'no soul' means it probably has excellent transients, drive, and high frequency extension.

[kev313]

Erik,

Yeah, that's the fun part...ummm the expensive part. By the way, I've been meaning to ask you a question. A while back you commented on the use of the 5y3 in the Wright 2a3. I have the Wrights and I have never heard the moondogs. What is your impression of the use of the different tubes in this psotion? Objectively and, if you've heard the wright 2a3, subjectively as well.

I must confess that my ignorance of the 5y3 exceeds my baseline tube ignorance. Do you know of any difference between types of 5y3 tubes??

Dean,

You were the one that recommended the kr tube to me in the first place. As I said, then Kelly steered me in another direction. A good one, to boot. I think. Oh hell, I really won't wax about "bloom" or the detail of one tube vs. another. I CAN say my nos rca from brent sound better than my sovtek. AND they both sound better than the crazy tj 300b - esque tube for 2a3 amps did (those came with my wrights from my seller). Why? Cause I think so.

Also, your subjective comment (which, as you can see, I HAVE TO believe is true to some degree or else I will soon go mad at this!) is at odds with your last comment on "soul" vs. "drive," etc. I think you may me driving yourself (have driven?) mad as well.

[jazman]

erik,

Changing to the 5AR4 rectifier will have a large influence on the sound and character of your Moondogs. I have been doing a lot of tube rolling of NOS Amperex 5AR4s, Mullard GZ34s, Philips miniwatt GZ34s, and metal base Mullard GZ34s in my Moondogs to compare with the Mullard GZ37s. Beware that some of the changes may be related to the rectifier change. I'm willing to share my notes on the NOS 5AR4's and GZ34s.

Klipsch out

[sprocket]

Interesting talk about the KR 2a3. Is it still offered.

www.kraudio.com seems to have droped it from their listings.

Jazman or Erik which rectifier tube passes more voltage the gz34 of gz37 ?

[Erik Mandaville]

Jazman, Dean, et al.:

I've been swapping out 5AR4s, GZ37s, 5Y3S, and one other 5-volt filament rectifier over the course of several years. The GZ37s are what came with the amps. About 5 years ago I bought some very expensive NOS RCAs, and through the kindness of my dad came into a beautiful matched pair of NOS GE 2A3s. These are antique tubes we are talking about. The RCA manual for max. plate voltage for a 2A3 used as a single-ended amplifier is 250. Built according to the schematic and kit instructions, my Moondogs had about 325 VDC (plate-to-cathode). I wanted to preserve and care for those expensive old tubes as best as I could, and made the decision to lower all B+ voltages. Before I did so, however, I contacted Ron W., who said "...spec sheet voltages are over-rated." Meaning, he didn't really think 50-75 more volts on the 2A3 was a problem. Despite his obvious knowledge and experience, I did not agree with that philosophy, and went about make the changes. George Wright wrote me an informative email a few months back, in which he indicated a preference for less aggressive voltages, as well. For reasons I'll not get into here, it was about that time that I was seriously considering selling my Moondogs-- I got angry when I looked at them. I had read some reviews on the Wright 2A3s that were nothing short of very flattering; and I have a good friend in Oregon, with many, many years of experience who liked the Wrights better than his Welborne Moondogs, better than his Welborne Laurels, and better than his Fi-X and Bottlehead amps. This gentleman, who is close friends with George Wright, described the day when George brought his most recent 2A3s (with 5Y3 rectifer) over to my friend's house to audition. Without getting into all the usual descriptive audio-speak, he said his jaw about hit the floor when he powered up those Wright 2A3 amplifiers. I am still seriously considering getting a pair of Wrights for myself, but just prefer on building my own. George Wright also uses fairly conventional parts in his amps, and the circuit, at least from what I have seen inside, is simple. To me, the real talent in audio design and engineering, as it is in art, is being able to make a great-sounding amp or preamp with as few parts as possible. I would absolutely hold onto those wright amps, Kev!

So, instead continued use of the powerful GZ37 and altering voltages by way of increased resistance (which does nothing but create heat), I decided to use a more moderate rectifier. I looked at many, and decided on the 5Y3. I want to point out, too, that even a 5Y3 offers more than what is needed for the job, and still required a good voltage dropping resistor. Wanting to maintain as close a balance to the original schematic as possible, I also changed the values of the plate resistors in the input and driver stages. And the 5Y3 has been very satisfactorily used for years.

The reason I have used the 5AR4 with the KRs is because they are such a ruggededly built tube. They are easily up to handling even more than the additional votlage imposed by the above tube -- and then some! I honestly do not need any more power! As it is, my Lowthers and La Scalas can send me running for the volume control if the preamp is accidentally turned up too loud. The volume, though undistorted and totally clean, can get to the point where it hurts my ears..........with just a couple of watts!

Erik

[Dale W]

ERIK: I'm very happy running the 5ar4 in my mark III's and even the 5r4 in jeff's pre-amp .

Olny problem i have with this tube is the price tag of a NOS OR NIB TUBE. I watch e-bay daily but refuse to pay $80.00 to $150.00 per tube ( mullard).

If you or anyone else here has a source for NOS 5ar4 ( mullard) tubes at a decent price i'd be more than gratefull for the info.

DALE

[Erik Mandaville]

Jazman: That's great you took some careful notes on those tubes. I honestly have much less experience with different brands -- which I know is important. I just haven't been in the position to purchase enough different kinds to get a solid hold on the subtle differences among them. So, that you took the time to document some of those perceptions and impressions is an excellent resource.

I know all tubes were and have not been created equally; and would love to learn some more about those 'inequalities' from someone with obviously more experience.

Erik

[leok]

A lot of interesting info on 2A3s and rectifiers. I like kev313's description: "AND they both sound better than the crazy tj 300b - esque tube for 2a3 amps" I'm using the TJs as my everyday workhorse. They're fun, but I can't make a lot of sense out of them however they're driven. On the other hand, old RCAs and TungSols are very well behaved.

The rectifier contribution is something I haven't begun to appreciate. I have 1942 vintage 5U4Gs in the amps now. I promised jazman I'd pay more attention when I change back to the CV378 (I can't remember which GZ3? that is) that came with the amps. Some time when I have a day or two and get those TJs out of there. By the way, I got the old 5U4Gs at http://www.halfin.com/shop/index.htm .. an interesting site. Michael, who generally answers the email, is knowledgeable and helpful.

Erik, which tube parameters are you using to determine voltage change? I couldn't see much difference in any of the rectifiers, but maybe wasn't looking in the right place.

leok

[Deang]

"The volume, though undistorted and totally clean, can get to the point where it hurts my ears..........with just a couple of watts!"

You just think it's undistorted. If it was really clean, it wouldn't hurt your ears.

The Welborne Apollos at 18wpc would have me gritting my teeth at 95db. The 60 wpc Quicksilvers can take me to 110 db with no strain to my ears whatsoever.

With just under 4 watts to begin with, there is constriction and clipping. SET just makes the clipping tolerable -- but it's not 'clean'.

SET sounds awesome -- but I don't think anyone should kid themselves regarding the compression of dynamics at anything more than a watt.

[NOSValves]

Deano,

You hit the nail dead on the head with that one !! SET is what it is. Spouting it to be anything other is just silly and misleading.

Craig

[Erik Mandaville]

Leo:

The difference in voltage provided by the 5Y3, GZ37,and 5AR4 is not substantial. I am going by readings taken with the stock Moondog circuit. I had a couple of different rectifiers (from restorations, etc.) on hand, and just tried them out to see what would happen. With the GZ37, plate to ground voltage is 351, compared to the 361 with the 5AR4. I used 5Y3s with my vintage RCAs, but adjusted the values of the plate resistors on the 6SN7s, and did a couple of other small changes here and there when I was using that tube. For all intents and purposes, the circuit is bascially stock, and I'd be glad to pop in a 5Y3 this morning and send you the result. I'm interested myself, since I can't remember exactly...

B+ voltage increase of just 10 volts is probably not enough to be significant. I was just aware of the fact that the KRs are rugged enough to be able stand up to a little more power, and so opted for the slightly stronger rectifier. Soundwise, I honestly haven't given a great deal of attention to the impact of rectifier tubes, and believe more pronounced changes can be detected by tube rolling in the downstream parts of the circuit. But that's just my opinion.

We listened to some music more heavily-laden with bass last night, and the KR tubes sounded very good. Marie and I usually listen at more moderate volume levels, but we turned things up a bit last night. Music from artists such as the 'California Guitar Trio,' Michael Hedges, Pat Metheny, 'Days of the New,' 'Audio Slave,' and some others...all came through with profound distortion and gross compression. As things progressed, I began to realize that this 2 or 3 watt adventure in hollow state technology was nothing but a silly waste of time. My dogs ran from the room with their tails tucked under their legs; my wife left the room quietly crying; and I decided to throw my amplifiers from the second-story window. In short, it was a night to remember.

Actually, the amplifiers are already warming up, and we look forward to another day of listening to the really fine KR Enterprise 2A3s!

Have a good Sunday!

[Triode Pete]

"The Welborne Apollos at 18wpc would have me gritting my teeth at 95db". Obviously, those amps (or pre-amp, or associated equipment, etc) had a serious problem (defect?) in them. Also, those amps are not in the same class as a good, 2A3 or 300B SET, a true SET!

Whereas some vintage amps and receivers (push-pull pentode, tetrode, etc.) may sound good, they cannot compare to the musicality of a good SET build & design. Unless your speakers are in a auditorium, the lack of headroom notion is pure bull**** (as PWK would say)!

I quote the master (Paul Wilbur Klipsch), "What the world needs is a good 5 watt amplifier!"

If one has not heard or experienced a good SET amp on very efficient full range speakers (I recommend Klipschorns or the Avantegarde line), one shouldn't pass judgment!

A sidebar on the original topic --- the KR 2A3 may sound fantastic on certain SET designs & manufacturers and may sound poorly on others. On my 300B amps, I prefer my KR 300BXLS tubes over other tubes. The KR line of tubes are robustly made with thick, heavy glass and a huge vacuum.

Have fun & enjoy,

Pete

[Erik Mandaville]

Triode Pete:

I agree on your thoughts on the build quality and ruggedness of the KR tube. It's probably the best built 2A3 I have seen, and it performed fantastically well in my Moondogs.

Thanks for sharing your thoughts on this subject!

Erik

[jazman]

Erik,

Are you spending any time listening to your other 2A3 tubes to provide perspective on the KRs ambiance. You mentioned in another post that you have a pair of vintage RCA Black plates, and another pair of vintage 2A3 tubes other than the Sovtek. I like the Sovtek tube, but I use my RCA Black plates for everyday tubes.

Klipsch out.

[Erik Mandaville]

Hi, Jazman:

Gosh, these tube comparisons for me are sometimes fleeting impressions -- other times more solid. It could depend on my mood, level of fatigue...who knows what else.

The Chinese 2A3s the amps came with were just sort of blah....nothing very interesting, but at the same time not bad. I have the dual-plate RCAs, but the way, and they were much better than the Chinese. I like the RCAs very much, and were the primary reason I lowered the B+ voltages in the Moondogs. Ron W. tends to run them quite high.

With the Sovteks, I have finally just been able to forget about listening to the damn tubes and enjoy the music. This is one thing I get on myself about: We start spending so much time talking about what different wire, capacitors, resistors, rectifiers, connectors etc. etc. etc., that the enjoyment of music becomes eclipsed by comparisons of components.

...and forgive me, Jazman! This is not directed toward you, and your question was one I have been pondering. I was at first struck by the great build quality of the KR, and then by what I perceived to be outstanding frequency response. It also seemed to have an uncanny ability to capture small musical details that I don't believe had come through so thoroughly with the Sovteks. I can say that they are both outstanding tubes, and I would give a nod to the Sovtek for its amazingly good cost/performance ratio. If money were not an issue, I would buy myself a pair of KRs today.

With all the tinkering and experimenting I do, I'm trying to make an effort to spend more time enjoying music. I've always got ideas floating around in my head, and tend to want to explore them.

I haven't heard the RCAs in awhile though! I should get those out this weekend for a listen.

I hope this helps at least a little bit....

Erik

...For the money, the Sovteks just can't be beat!!!

[jazman]

Erik,

I agree with the Sovtek normally holding the "most bang for buck" title. That said however, I was able to purchase several pairs of '43 and '44 RCA's at close to the price of Sovteks along with a pair of Rogers branded black plates. I also believe this is about MUSIC, and I spend most of my time at home listening to music, so it's really easy to roll in a couple of(any)tubes for a couple weeks at a time for extended listening and forget about which tubes I'm using. I am deinitely interested in hearing the KR2A3.

Klipsch out.