The higher is output resistance of the stage that drives non-linear Miller's capacitance, the more of phase intermodulations you are getting. The harder you try to compensate them by feedback, the further is driver stage swinging out of originally selected for lower distortions optimal working point.
Yes.
The driver stage is the most critical and demending portion in a DHT amp. Almost all DHT's (we commonly see) are inherently good in linearity and low distortion, but they are difficult to drive. Those DHT amps with overly warmth and tuby sound are probably badly driven. It's the sound of DHT? Not at all.
This is always a good read:
The Amity, Raven, and Aurora
The driver stage is the most critical and demending portion in a DHT amp. Almost all DHT's (we commonly see) are inherently good in linearity and low distortion, but they are difficult to drive. Those DHT amps with overly warmth and tuby sound are probably badly driven. It's the sound of DHT? Not at all.
This is always a good read:
The Amity, Raven, and Aurora
Has anyone built an 845 amp using an interstage transformer coupled 2A3 for the driver? I'm very curious to try this.
Ok, I am interested in the message from jrdmedford
I also like to build an 845 SE amp with lower plate voltage that commonly used. Main reason is that the 1000V really scares me a lot.
jrdmedford , in your message you mention '300B operating point'.
Can you be more specific?
Like what plate voltage and current.
Thanks
Phil Marchand
(smiles)
I also like to build an 845 SE amp with lower plate voltage that commonly used. Main reason is that the 1000V really scares me a lot.
jrdmedford , in your message you mention '300B operating point'.
Can you be more specific?
Like what plate voltage and current.
Thanks
Phil Marchand
(smiles)
You need to search ( & read ) on miller capacitance and slew limiting .
Getting clean results out of an 845 to full power needs about 40mA and at least 300V p-p of undistorted swing in the driver .
45 is the easiest to get beautiful results from - for similar reasons !
I see there is only two ways:
Small Triode(45, 2A3 or 300B) or Big Triodes (211, 845).
If you choose small Triode stick with the 300B(more power and better sound).
But if you choose the Big Triode amp, forget 211 & 845 tubes, the best sound Big Triode is the 805 Top Cap, it had a huge gain of 50, not 6 or 12, and is a very detailed tube.
If you can afford real NOS 805(if this dodo bird yet exist) go this way, avoid use chinese 805(unreliable).
In case you want a low priced Big Triode stick with the GM70, gain is 8, similar to 845.
The GM70 sound is immediate, warm, big, bold, oldfashioned, detail depend on the driver tube character, the Bias is stable like a rock.
Hope this help.
Thoriated tungsten filament triodes are in slightly different league. If one runs them "properly" they have something more than the rest, IMHO.....
If one doesn't want to use high voltage there is a much better alternative to big triodes run at low voltage and 2A3/300B. This is the 10Y/801A/VT-62.
One can run 845 and 211 at low voltage but I cannot see the point. It's a total waste for me. The filament only requires 32VA! Even worse with the GM70 (which is just as good) requiring 60VA!!
Among 45, 2A3 and 300B the 45 wins hands down. The limitation of low Pout of the SE can be overcome just going for a push-pull. This has to be experienced to understand why....😀
If one doesn't want to use high voltage there is a much better alternative to big triodes run at low voltage and 2A3/300B. This is the 10Y/801A/VT-62.
One can run 845 and 211 at low voltage but I cannot see the point. It's a total waste for me. The filament only requires 32VA! Even worse with the GM70 (which is just as good) requiring 60VA!!
Among 45, 2A3 and 300B the 45 wins hands down. The limitation of low Pout of the SE can be overcome just going for a push-pull. This has to be experienced to understand why....😀
Hi!
I am surprised who the sound of tube amp continuously gets reduced to the sound of the output tube. Each of the tubes mentioned can sound very different depending on the implementation.
However with some of them it is much easier and less costly to get excellent sound results. Among those the 45 is king since it is the easiest to drive and it's filament is more forgiving than thoriated tungsten types.
With the larger triodes (and I would count the 300B more to the larger category) the sound gets more and more dependant on the driver, which becomes very critical for 211 and 845.
In my experience the materials cost per watt stays pretty much linear.
Best regards
Thomas
I am surprised who the sound of tube amp continuously gets reduced to the sound of the output tube. Each of the tubes mentioned can sound very different depending on the implementation.
However with some of them it is much easier and less costly to get excellent sound results. Among those the 45 is king since it is the easiest to drive and it's filament is more forgiving than thoriated tungsten types.
With the larger triodes (and I would count the 300B more to the larger category) the sound gets more and more dependant on the driver, which becomes very critical for 211 and 845.
In my experience the materials cost per watt stays pretty much linear.
Best regards
Thomas
That is true for sure however you can do nothing about linearity and driving requirements. The 2A3 is less linear and the 300B is too demanding to the point that is better to go with 211 at 1-1.2 KV. That's my opinion of course.
I've tryed a lot of those big triods and also got the idea that it depends a lot of what is behind them and the iron you're using.
If you try to save on the driver, the outcome will be short of what you get with proper driver.
For all the big ones (211, 845, GM70) I got best results with high voltage (1100to 1250V) and a driver like a 300B, if possible via interstage.
If I need 200V swing to drive it, I will design it to reach more than 300V, and impedance low enough to drive capacitance without inpact on bandwidth or DF. Typicaly I use a 300B to drive the big guys. Tryed 45, 10Y, 2A3 and they all work well as drivers, but there is always some point that will not fullfill my needs.
So, I teel you the driver will have more impact on the sound than the final triode, if all else is properly designed.
If you try to save on the driver, the outcome will be short of what you get with proper driver.
For all the big ones (211, 845, GM70) I got best results with high voltage (1100to 1250V) and a driver like a 300B, if possible via interstage.
If I need 200V swing to drive it, I will design it to reach more than 300V, and impedance low enough to drive capacitance without inpact on bandwidth or DF. Typicaly I use a 300B to drive the big guys. Tryed 45, 10Y, 2A3 and they all work well as drivers, but there is always some point that will not fullfill my needs.
So, I teel you the driver will have more impact on the sound than the final triode, if all else is properly designed.
Hi Palmas,
I have very similar experiences like you describe...
I actually go for at least double, 6dB headroom often even more.
The best 211 amp I ever built had another 211 as driver
Best regards
Thomas
I have very similar experiences like you describe...
I actually go for at least double, 6dB headroom often even more.
The best 211 amp I ever built had another 211 as driver
Best regards
Thomas
It is the same the 300B. One needs to swing a lot of volts, even for 6-7W Pout, with quite some Miller capacitance to drive to get the best out of it hence the amp will expensive and somewhat complicated anyway. If one has to put so much effort in it then I think it is better to do it for the higher power and overall better performance the big triodes can give. For just 12-13 W, in best case, it is not worth for me. The problem with this valve is that it looks nice on paper but in practice it is not. Those data-sheet examples make it look so easy and desirable but in fact they don't work (sound) well. The problem is mostly the drive just as for the big triodes....
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