Tubelab, you got me wrong.
The thread starter want to build a simple two stage 300B amp.
What you prefer and have build isn't the same concept.
You build a three stage amp, and because of the whimsy input tube, you placed a low output impedance stage between this and the 300B. Totally different concept, and I have no doubt that it might work very well.
But with a simple two stage amp, that cathode follower stage isn't meant to be there.
From the theoretical books, a tube is a high impedance input device, which needs nearly no energy to run well. You'll see many of those concepts, an EF86 running another high power pentode and so on. Those all may function in theory, but as you figured out, the reality is much more complex and it has shown in measures, that even a 300B isn't that simple to drive as it may look like on the first lookout.
I prefer the concepts of Sakuma, because a cathode follower may work well, but its still a fully negative coupled circuit and everyone says, that cathode followers are not the best of all types of tube circuits. So why use a full negative coupled amp stage, when driving the output tube with a real beefy driver tube is possible and avoids all those problems?
To my ears, that sounds much better (and in fact, my ears count in this game much more than measures).
Sakuma did it the same way, for him, the best working point for a tube couldn't be found by the data sheets. He always auditions the tubes and found by simple hearing the best working points for his tube amps. He couldn't be so wrong, because his amps have a cult following in japan.
His concept of using the same caliber of tube for driver and output may be theoretical nonsense, but in practise it works out quite well.
The thread starter want to build a simple two stage 300B amp.
What you prefer and have build isn't the same concept.
You build a three stage amp, and because of the whimsy input tube, you placed a low output impedance stage between this and the 300B. Totally different concept, and I have no doubt that it might work very well.
But with a simple two stage amp, that cathode follower stage isn't meant to be there.
From the theoretical books, a tube is a high impedance input device, which needs nearly no energy to run well. You'll see many of those concepts, an EF86 running another high power pentode and so on. Those all may function in theory, but as you figured out, the reality is much more complex and it has shown in measures, that even a 300B isn't that simple to drive as it may look like on the first lookout.
I prefer the concepts of Sakuma, because a cathode follower may work well, but its still a fully negative coupled circuit and everyone says, that cathode followers are not the best of all types of tube circuits. So why use a full negative coupled amp stage, when driving the output tube with a real beefy driver tube is possible and avoids all those problems?
To my ears, that sounds much better (and in fact, my ears count in this game much more than measures).
Sakuma did it the same way, for him, the best working point for a tube couldn't be found by the data sheets. He always auditions the tubes and found by simple hearing the best working points for his tube amps. He couldn't be so wrong, because his amps have a cult following in japan.
His concept of using the same caliber of tube for driver and output may be theoretical nonsense, but in practise it works out quite well.
Last edited:
Just wanted to add my experience on this, first time I saw this thread and apologies that haven't read it all.
I currently have a 2 stage no-compromise 300B Amp with DHT driver. I started the journey last year with a D3a driver and experimented with few valves.
From an IHT point of view as said before either D3a or E801F triode wires are great choices amongst few other ones. However, when you replace the driver with an DHT driver, you can still notice the difference in extra sound detail, image, etc.
Not as important as a preamp, but DHT in the driver stage is key in my experience.
Everyone knows I'm a big fan of the mu-follower topology and leveraged the best of both worlds in my view on my design.Currently working with 47, already tried it with 801a, 46 and VT-25. Any good mid-mu DHT will work really well.
1) I use a good quality large-signal SUT (like LL7903) - which isn't cost prohibitive and easy to implement. With a gain of 1:8. Yes, you need a low source impedance - there is no free lunch. Not a constraint with a lot of the digital volume controlled devices out there and DACs. I use a Slagle AVC
2) with a hybrid mu-follower you can un-bypass the cathode cap and use valves with large bias voltage which ruled them out in filament bias. This is a real plus
3) The hybrid mu-follower has the grunt to drive well the 300B, which isn't a very demanding load but you want optimal performance to 200Vpp
If you're interested you can read more here:
300B/845 Amp: Driver Options – Bartola(R) Valves
Just my 5-pence. Stay Safe
Ale Moglia
I currently have a 2 stage no-compromise 300B Amp with DHT driver. I started the journey last year with a D3a driver and experimented with few valves.
From an IHT point of view as said before either D3a or E801F triode wires are great choices amongst few other ones. However, when you replace the driver with an DHT driver, you can still notice the difference in extra sound detail, image, etc.
Not as important as a preamp, but DHT in the driver stage is key in my experience.
Everyone knows I'm a big fan of the mu-follower topology and leveraged the best of both worlds in my view on my design.Currently working with 47, already tried it with 801a, 46 and VT-25. Any good mid-mu DHT will work really well.
1) I use a good quality large-signal SUT (like LL7903) - which isn't cost prohibitive and easy to implement. With a gain of 1:8. Yes, you need a low source impedance - there is no free lunch. Not a constraint with a lot of the digital volume controlled devices out there and DACs. I use a Slagle AVC
2) with a hybrid mu-follower you can un-bypass the cathode cap and use valves with large bias voltage which ruled them out in filament bias. This is a real plus
3) The hybrid mu-follower has the grunt to drive well the 300B, which isn't a very demanding load but you want optimal performance to 200Vpp
If you're interested you can read more here:
300B/845 Amp: Driver Options – Bartola(R) Valves
Just my 5-pence. Stay Safe
Ale Moglia
It's certainly wrong to say that a 300B triode isn't a demanding tube when it comes to driver stages.
There are easy to drive tubes, but a 300B is not, when it comes to top performance.
A mediocre sounding 300B amp is what you can find all around. But top performance is requires different amps, and even your opinions on the driver stages is just the opposite of an easy to drive tube.
I once read an article on the reasons for that, and that declares why its so demanding.
Thats why people do research on that topic, its not as easy as it seems when you go one stage deeper than the usual superficial calculation on the fast track for any tube amp.
There are easy to drive tubes, but a 300B is not, when it comes to top performance.
A mediocre sounding 300B amp is what you can find all around. But top performance is requires different amps, and even your opinions on the driver stages is just the opposite of an easy to drive tube.
I once read an article on the reasons for that, and that declares why its so demanding.
Thats why people do research on that topic, its not as easy as it seems when you go one stage deeper than the usual superficial calculation on the fast track for any tube amp.
I didn't say "isn't a demanding", I said " isn't a very demanding" one. 
Certainly there are other valves (e.g. transmitting valves) which have higher demands in terms of grid current and even worse much higher miller capacitance.
"even your opinions on the driver stages is just the opposite of an easy to drive tube."
perhaps it got lost in translation, I never said it was an easy valve to drive.
There are plenty of bad 300B amplifiers out there, that is the reason why sometimes it get bad reputation.
Anyhow, better turn the discussion on interesting stuff
Certainly there are other valves (e.g. transmitting valves) which have higher demands in terms of grid current and even worse much higher miller capacitance.
"even your opinions on the driver stages is just the opposite of an easy to drive tube."
perhaps it got lost in translation, I never said it was an easy valve to drive.
There are plenty of bad 300B amplifiers out there, that is the reason why sometimes it get bad reputation.
Anyhow, better turn the discussion on interesting stuff
This is all true. And thats why the best driver/Tube discussion is just one piece of the whole puzzle.
Once I build a stereo 300B amp. It was good, better than strong competitors. The interested customer asked: how did you do that? Whats the magic behind it? It was nothing special, just excellent, choosen parts and a fine tuned, three stage 300B amp with a beefy driver. But that alone was enough to make it better. So I knew, it doesn't need the most refined circuit, its just a combination of doing things in the right manor, not making faults or compromises that other commercial manufacturers have to do all day long.
The best is just good enough. The hi-fi industry claims this often enough, but it is prescribed by the marketing department. There are power amplifiers on the market for tens of thousands of euros, where 500 euros for the power tubes were already too much money, too expensive. Of course nobody says that. The advertising prefers to speak of "manufactured according to our own specifications and strictly selected".
Today, after some decades later, I could do better. Enhanced circuit skills, better components, refined production methods.
But why build another 300B tube, this is so sought after, so much overprized and there are literally hundreds of other excellent tubes around, sometimes for pennies. So I made the decision, with a budget amp, most investment has to be gone into hardware, not tubes. And that pays of a lot!
If one ever goes the 300B ultimate amp route, he (or she) has to have deep pockets, otherwise the best circuit isn't up to the compromises the amp designer has to do on the rest of the parts.
Its just one Western Electric tube type, but to get the best out of it, the most refined sound, its just not that easy.
Once I build a stereo 300B amp. It was good, better than strong competitors. The interested customer asked: how did you do that? Whats the magic behind it? It was nothing special, just excellent, choosen parts and a fine tuned, three stage 300B amp with a beefy driver. But that alone was enough to make it better. So I knew, it doesn't need the most refined circuit, its just a combination of doing things in the right manor, not making faults or compromises that other commercial manufacturers have to do all day long.
The best is just good enough. The hi-fi industry claims this often enough, but it is prescribed by the marketing department. There are power amplifiers on the market for tens of thousands of euros, where 500 euros for the power tubes were already too much money, too expensive. Of course nobody says that. The advertising prefers to speak of "manufactured according to our own specifications and strictly selected".
Today, after some decades later, I could do better. Enhanced circuit skills, better components, refined production methods.
But why build another 300B tube, this is so sought after, so much overprized and there are literally hundreds of other excellent tubes around, sometimes for pennies. So I made the decision, with a budget amp, most investment has to be gone into hardware, not tubes. And that pays of a lot!
If one ever goes the 300B ultimate amp route, he (or she) has to have deep pockets, otherwise the best circuit isn't up to the compromises the amp designer has to do on the rest of the parts.
Its just one Western Electric tube type, but to get the best out of it, the most refined sound, its just not that easy.
Last edited:
I've used DHTs in every amp or preamp I've made since 2008. I was religiously bound to their charm and transparency. My daily amplifier right now is a 2 stage one and I like it a lot. No DHTs. Very good tubes from the late '30s. I never thought I'd see the day when my DHTs stayed in their boxes, but there we are. I'll go back to the 300b when I find a driver stage that I really, really like. I'm still actively searching, but I'm not holding my breath. It may happen but what I have now is really good.
since the cathode followers, and the source followers are lower than unity gain stages, to me they do not count as a "gain" stage.....
to me the real challenge to the diy'er is to get the best sound at the lowest possible cost, that will be a though act to follow....
if you spend a ton of money on an amp it is natural to expect a ton of sound whatever that meant.....
to me the real challenge to the diy'er is to get the best sound at the lowest possible cost, that will be a though act to follow....
if you spend a ton of money on an amp it is natural to expect a ton of sound whatever that meant.....
Well, as above there's also the question of cheaper tubes and expensive iron! Output transformers and plate chokes make quite a difference. Especially if you go amorphous or nickel or other quality construction. The money you put into 300b tubes, which will need replacing, could arguably be better spent on really good iron.
Unfortunately, the outcome of those "high end, ton of money" amps is, if it comes to commercial ones, often just a desaster. They tend to sound sterile, overdesigned, overcomplicated and overengineered. They often have lots of power, what means very complex PSU and circuits, which leads straight towards the complex design circuits of transistor amps, just with tubes.
Most of them I listened to in audio fairs are just good enough to enjoy the silence, when it was switched off.
An easy to drive tube, low wattage, simple PSU is, in most cases and with the right LOUDspeaker, in advantage. Easy to design, high eff. speaker combination which just fits in, its most often a winner combination. But that couldn't be showed at audio fairs. Nobody who makes big money with that...
Could be very low in cost and plays wonderfull music. A german designer, Götz Willimzig, has proofed to better a 300B amp with just a simple PL82 tube. When it comes to real music value, the 300B had a hard time to beat the tiny PL82. It simply was more musical sounding as the legendary tube. Still cost just pennies. But you need the right speakers for it.
Last edited:
I think that 300b with single stage is no possible, to have a good amp.
300b need 90v to drive in class A1 in this case is only possible with interstage 1:2
all as triode, 300b do not need low impedance source, I listen and made 6sn7 x 6sn7 x 300b with a fantastic sound. no need more. Bur if want to avoid one stage, my target would be:
D3a 1:2
E180f 1:2
c3g 1:2
6e5p 1:3
I have implemented in the past 6ac7 mu 50 very lineal as Ri similar triode, I don´t think that be worse than the famous c3g
300b need 90v to drive in class A1 in this case is only possible with interstage 1:2
all as triode, 300b do not need low impedance source, I listen and made 6sn7 x 6sn7 x 300b with a fantastic sound. no need more. Bur if want to avoid one stage, my target would be:
D3a 1:2
E180f 1:2
c3g 1:2
6e5p 1:3
I have implemented in the past 6ac7 mu 50 very lineal as Ri similar triode, I don´t think that be worse than the famous c3g
90V is just one of many possible operating points.
I'd say 140V pk-pk is more common, requiring 50 VRMS for class A1.
But even with 180V pk-pk (64 VRMS), with a C3g and a 1:1 interstage transformer you would need 1.6 VRMS at the input which is quite normal with digital sources.
Many seem to forget that a C3g can withstand at least 2 VRMS grid voltage; D3a/E810F cannot.
I'd say 140V pk-pk is more common, requiring 50 VRMS for class A1.
But even with 180V pk-pk (64 VRMS), with a C3g and a 1:1 interstage transformer you would need 1.6 VRMS at the input which is quite normal with digital sources.
Many seem to forget that a C3g can withstand at least 2 VRMS grid voltage; D3a/E810F cannot.
I think that is very danger a driver that need the 100% to move 300b normally to have a good headroom, need x 1.5 to x2 140vpp = 210vpp minimun
Few years ago I measured some C3g tubes (360V B+, CCS loading, 240Vpp , Out THD):
240V pp 0.86 0.79 0.84 0.93 0.68 0.635 0.5 0.81 0.66 0.58 0.67 0.58 0.53 0.68 0.33 0.96
Hello,
Last year i made SE 300B amplifier. I tried in driver, EC8010, C3G in triode, C3M i
The best result to THD and bandwidth is the EC 8010. I worked with This tube forSPUD AMP.
In driver, this tube have microphonic effect it's not the case of C3G.
The amplifier factor of C3M in triode it's not enough.
I worked with C3G.
Eric
Last year i made SE 300B amplifier. I tried in driver, EC8010, C3G in triode, C3M i
The best result to THD and bandwidth is the EC 8010. I worked with This tube forSPUD AMP.
In driver, this tube have microphonic effect it's not the case of C3G.
The amplifier factor of C3M in triode it's not enough.
I worked with C3G.
Eric
Last edited: