[JoshK]

An example of a 2 stage 300B amp that has a driver with the guts to get er done:

Wavelength amp on Audiogon

Note the price tag.  Unfortunate consequence for many such amps.

[jrebman]

I agree with Josh, it's not the tube, it's the implementation of the amp.  One very interesting approach to a 300b design is the Axiom amp, which I'd really love to hear one of these days:

http://www.chimeralabs.com/chimera_labs_axiom_300B_single_ended_set_tube_amp.html

With this topology these guys are getting distortion measurements that rival those of good SS designs, and the reports from the listening tests sound very impressive.  This amp is totally direct coupled from input to output with no caps or resistors in the signal path.  They are also working on a lower power, pentode monoblock version that should be a lot more affordable too.

The Wright Sound Mono7s I just bought, but haven't been able to play yet, are also supposed to have some interesting design features which make them sound more like 2a3s than 300bs (in a typical, underdriven 300b design).  Bud Purvine, who designed and builds the transformers for these says this is a 300b he can live with as he generally doesn't like 300b amps either.  Can't wait to find out for myself.

-- Jim

[JoshK]

Thanks Jim, hadn't seen that one before.  They obviously take the care to do it right.  I'd probably choke on the price tag, which is why I got into the hobby of building my own.  However, I probably spent just as much over longer periods of time.  The Karna amp has probably $4K invested in it so far.

Josh

[iGrant]

Blair, were are you, building a 300B amp? see how much fun and debate, not much catches the interest of the tube world as a new 300B offering, do something different with it, like someone did with a EL-34 driver stage and see what happens.

Great thread, every post is a worthy read.

Cheers,
Ian

[Rocket_Ronny]

Joshk:

Now I am going from memory,  but seems that what was said is that the 300B rise time was slow, as in the tube itself, and that it was a poor tube choice to design an amp around. Everyone has their opinions I guess.

I forget what driver stage the Sun Audio had. But I can tell you that I found the amp to be boring over time. Maybe a solid state pre is what was needed. No doubt a Wavelength would be a better amp. Would love to hear one, but would never shell out the coin for 8 watts. Can anyone share the sound characteristics of a properly designed 300b amp? Most people say the 300b amp is for the midrange as the highs are soft and the bass mushy, usually. Too much sacrifice for me.

Rocket_Ronny

[Watson]

I use the tube in both a headphone amp (single stage xfrmr output) and a power amp (ECC99 xfmr coupled to the 71).

Is this a headphone amp of your own design? I've been interested in using the 71 for a headphone amp.

[Quiet Earth]

.... would never shell out the coin for 8 watts.  

Rocket_Ronny

Rocket_Ronny,

Occasionally I'll have friends over and after a little bit of listening to music I'll ask them if I should turn it up. "Oh, no that's plenty loud" they say. Then I tell them that it's only 8 watts per channel making all of that music.  Believe it or not, that kind of ruins it for them.   Maybe I should tell them that it's 100W and they can get back to saying "damn! that sounds good.".   Anyway, I think it's only natural that we let our rules get in the way of stuff that actually works.

As you know, power is relative to the speaker that it's powering, so if it plays loud enough with 8 watts then having 1OO more won't necessarily improve things. You know what they say about the first watt. I think we put too much emphasis on power these days and not enough on gain staging and system building.

Back to the root of this thread, I think the problem with saying that a 300B is good or a 300B is bad is that we are not taking the entire system into context, let alone the design of the amplifier. We could just as well have the same argument over tube vs. transistor, vinyl vs. cd etc. If we are wondering whether the 300B is "worth it" in the context of its cost, availability, and access to the necessary parts to make it work right, then that's a different story.

FWIW, my 300B amp doesn't sound slow, fast, accurate, spacious, warm, linear, compressed, or any of those things mentioned. It just sounds right.

[Rocket_Ronny]

Hey Earth, Wind, and Fire: 

Maybe you could share a bit of your rig. What amp are you running and with what system? 

Well, that Wavelength posted earlier was around 4 grand. I paid almost half that for 2.5 watts before. So I am not downing the watt per dollar issue. It's just that I am out of the high eff. single driver club, and most speakers that interest me are around 87 to 91 db, except for a speaker based on the P-Audio driver at 97 db. So, unless I could find a high eff. speaker that turns my crank I would need more power.

My experience with 300bs is very limited. Just sharing what I have heard.


Rocket_Ronny

[Niteshade]

No, I'm not building one yet but plan on starting out with a push-pull 300B. Triodes have an allure technically because they're so simple. The fact that some of them are difficult to drive means they will reject noise due to their natural attenuation of the input signal. Put that together with a push-pull setup capable of rejecting more power supply noise than a single-ended amp and WOW! You get plenty of power, that triode magic and a quiet amp! 

I see lots of potential here and if made properly, a push-pull 300B amplifier will be a killer amp with tubes in it made for the long run. This is exciting and I can't wait to begin the project! I wish the 300B had an indirectly heated cathode...oh well.

Around the same time I'd like to start designing an amp around the 6AS7/6080 triode tube.

Blair, were are you, building a 300B amp? see how much fun and debate, not much catches the interest of the tube world as a new 300B offering, do something different with it, like someone did with a EL-34 driver stage and see what happens.

Great thread, every post is a worthy read.

Cheers,
Ian

[Quiet Earth]

 I know it's not easy to piece together a winning amplifier speaker combo based on what you read. I have tried before and failed myself.

So, unless I could find a high eff. speaker that turns my crank I would need more power.

Rocket_Ronny

Or,,,,,, unless you could find a dealer (or a friend) that has a great amplifier/speaker combination already put together then you could just get that. This is what happened to me a few years ago. I went to my local hifi shop just to hang out with the guys and about an hour or so later I realized that I was enjoying music way more than I ever did at home with my Electrostats and push pull amp. I went home kind of perplexed because my core beliefs were challenged. I went back to the store later just to make sure that I wasn't delusional. I decided right then and there that I would sell my stuff and get exactly the combination that the dealer had assembled. I decided that I was going to go with exactly what I heard, not with what I thought made sense to assemble.

I guess that's all I was really trying to say earlier. You have to hear it done right first, and then you have to let go a little and accept it.

I didn't really want to throw my laundry list out there because sometimes name brands can evoke prejudices, good and bad. Also, there's a lot of stuff out there that works just as well, if not better than what I have. And lastly, in keeping with my message, you really need to hear it to decide if it's right for you or not.

OK, having said all that, fair is fair. If I'm gonna spout off I suppose I should also share what I'm using. My amps are Audio Note Quest silver signatures and the speakers are Zingali Overture .4s. THe CD player is also Audio Note, but I have no pre amp, just a TVC from DIY HiFi Supply. I occasionally spin vinyl too, but we'll just leave it at that for now. 

[Quiet Earth]

I see lots of potential here and if made properly, a push-pull 300B amplifier will be a killer amp with tubes in it made for the long run. This is exciting and I can't wait to begin the project! I wish the 300B had an indirectly heated cathode...oh well.

Niteshade,
Thanks for starting this thread. I sort of got all caught up in it, if you can't tell already. Anyway, I guess you got your answer. It's worth it! FWIW, I think the world will be a better place with another 300B amplifier to choose from  . Seriously. 

Jump in, the water is fine!

[JoshK]

The fact that some of them are difficult to drive means they will reject noise due to their natural attenuation of the input signal.

Explain that one.     If the Av is greater than one how is this possible?  Unless, your driver is slew limited and you are talking about VHF.   I get the common mode rejection part (PSRR), but attenuation of noise on input?

[JoshK]

Joshk:

Now I am going from memory,  but seems that what was said is that the 300B rise time was slow, as in the tube itself, and that it was a poor tube choice to design an amp around. Everyone has their opinions I guess.

I don't think that is right.  But I am going to defer since I can't refute that 100% technically, I'll have to come back when I've verified my facts.  Maybe some engineer can help out.

[Niteshade]

Josh,

What I meant was that if something is difficult to drive, then it's less apt to pick up noise.  I noticed this with the 6N7.

[dado5]

Is this a headphone amp of your own design? I've been interested in using the 71 for a headphone amp.

You  have a PM.

[JoshK]

Joshk:

Now I am going from memory,  but seems that what was said is that the 300B rise time was slow, as in the tube itself, and that it was a poor tube choice to design an amp around. Everyone has their opinions I guess.

I don't think that is right.  But I am going to defer since I can't refute that 100% technically, I'll have to come back when I've verified my facts.  Maybe some engineer can help out.

If your interested, pm me and I'll point you to a discussion that explains this.  The short answer is that the rise time of the 300B is not "slow" as it pertains to audio, its actually quite respectable.  It really comes down to the driver stage as I suspected.

[Niteshade]

An observation about tubes:

I think of tubes as tools, such as a hammer, saw, screw driver, etc... Better quality tools are more reliable and easier to use. At the same time, these tools can be used correctly or incorrectly. If it's used incorrectly, the tool cannot be blamed for the results.

So- with tubes, the 'flavor' of the tube might not be accurate depending on how it was implemented. The best thing to do is to stay away from generalizations. Others here have pretty much said the same thing. I wanted to interject this regarding the 6N7, 6BL7 and 6SN7GTA series of tubes. Someone said the 6SN7 was a better sound tube than the GTA or GTB series. They're all very good- but they are different 'tools' and that's how they have to be viewed. 

The circuit is the key and using the right component for the circuit is key as well.  Substitutes are not always decent substitutes. Some circuits are VERY critical as to what's placed in them and tubes like the 300B I would have to believe are extraordinarily 'picky' about what it takes to make them sing like they should. Being picky isn't a bad thing- it just means the designer has to put forth some extra effort to make it work 100% perfectly. So far, I enjoy working with power triodes- and my work with them has aided me in upgrading my pentode-based power amplifiers.

R&D is NEVER finished! (Thank God!!!) 

[Plink]

Plink,

Take a look at Alan Kimmel's mu-stage and George of Tubelab's powerdrive circuitry.  These are the SRPP concept on steroids, especially George's.  They go one step further in allowing more current to drive the output on demanding peaks, but in normal passages are similar to an SRPP in many ways.

Thanks Josh, I will *definitely* do that.

[Quiet Earth]

An observation about tubes:

I think of tubes as tools, such as a hammer, saw, screw driver, etc... Better quality tools are more reliable and easier to use. At the same time, these tools can be used correctly or incorrectly. If it's used incorrectly, the tool cannot be blamed for the results.

So- with tubes, the 'flavor' of the tube might not be accurate depending on how it was implemented. The best thing to do is to stay away from generalizations. Others here have pretty much said the same thing. I wanted to interject this regarding the 6N7, 6BL7 and 6SN7GTA series of tubes. Someone said the 6SN7 was a better sound tube than the GTA or GTB series. They're all very good- but they are different 'tools' and that's how they have to be viewed. 

The circuit is the key and using the right component for the circuit is key as well.  Substitutes are not always decent substitutes. Some circuits are VERY critical as to what's placed in them and tubes like the 300B I would have to believe are extraordinarily 'picky' about what it takes to make them sing like they should. Being picky isn't a bad thing- it just means the designer has to put forth some extra effort to make it work 100% perfectly.

Amen to that brother! 

[Triode Pete]

I have a 71A Stereo Single Triode Linestage Preamplifier with separate dual regulated tube power supplies. Extremely sweet sounding with just enough gain. Toughest part is getting non-microphonic 71A tubes. Currently using a pair of RCA Radiotron UX-171A globe triodes. The ST-shape ones were too microphonic.

The one pair of globes I have is more microphonic than my ST bottles, but they all vary quite a bit and all are more microphonic than a 300b for sure.

Is the preamp transformer or RC coupled at the output?

I use the tube in both a headphone amp (single stage xfrmr output) and a power amp (ECC99 xfmr coupled to the 71). The amp will run out of gas much sooner than  300b's on the same speaker, but I never actually get there in normal listening - I would guess my average listening level is in the mid 80's which translates to 50, maybe 100,  milliwatts on my 101dB speakers. This is also a reason why a low power operating point worked so well with the 300b in my set up.

BTW, I agree with your profile comments on power conditioning - it's never improved a system I've had and made things worse more often than not.

Dado,
My 71A preamp is RC coupled. Part of the magic of the of the low (~20 dB) gain preamp can be attributed is the sweet sounding Gen-Rad Laboratory grade 1201B tube regulated power supplies.

Speaking of preamps, I also own (I guess I used to) a transformer coupled Western Electric 437A preamp on a Euridice chassis. One of my favorite line stages ever...once again, my brother-in-law has possession of that one as well...

Cheers,
Pete