Single-Ended Triode (SET) Amplifier Revolution of the 1990s. Did it really happen? Was it Successful?
- Thread starter caesar
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This thread is about Single-Ended Triode amplifiers and the Audiopax 88 is not a single-ended triode amplifier. It uses a KT88 as the output tube which is a Beam Tetrode design. Also, single ended triode amplifiers, the ones used in the classic implementation, as in 2A3, 300B, 211, 845 etc have common cathode to filament connections. This means in these types of triodes the filament supply is in the audio circuit because the cathode and filaments are internally connected within the tube, meaning the filament supply has a big impact on the output stage with regard to signal to noise. The KT88 being a beam tetrode has a separate filament from the cathode so they are not internally connected like in the triodes above. This enables the use of a separate AC supply for the filament for the KT88, so a much simpler implementation. For low noise operation a DC supply is pretty much mandatory in a SET design. However, the triode is a much more linear device than a beam tetrode, which is why triodes are the preferred tube of choice for best audio performance. Interesting to see what Stereophile thought of the 88 and the use of timbre lock with regard to what it actually did: https://www.stereophile.com/content...-eight-monoblock-power-amplifier-measurements
FWIW I met Eduardo de Lima several times during my time with Avantgarde and had nice conversations with him about amplifiers and audio in general before his sad passing in 2012...
I have been working in the audio field since the early 1980s, so about 40 years. During that time I have repaired pretty much every make and model of high end amplifiers produced around the world. I also imported Avantgarde speakers into the UK for 17 years and in this time I had about 7-8 UK dealers. The overriding question I used to get was "what amplifier can I use to drive the Avantgarde horns to limit the noise produced". These dealers pretty much had every type of amplifier at their disposal. I too have had every type of amplifier through our demonstration studio, which is why I made the comment about amplifier matching being absolutely critical for optimum audio performance.
Actually, Jim imported Viva amplifiers long before he imported Audiopax into the USA.
To be clear the tubes mentioned above do not have a distinct cathode. The filament is the cathode, hence the term Directly Heated Triode (DHT).
Well you might want to do some research and look at who makes what in high-end audio to see what tubes they use. I think that should clarify things nicely for you...
But just to confirm it for you, the best performance is achieved with the following configuration.
1. Directly heated Triodes in single-ended configuration.
2. Directly heated Triodes in parallel single-ended configuration
3. Directly heated Triodes in push-pull configuration
4. Indirectly heated Triodes in single-ended configuration
5. Indirectly heated Triodes in parallel single-ended configuration
6. Indirectly heated Triodes in push-pull configuration
7. Pentode/Beam Tetrode in single-ended configuration.
8. Pentode/Beam Tetrode in parallel single-ended configuration
9. Pentode/Beam Tetrode in push-pull configuration
The only reason a pentode or a beam tetrode would be used in a single ended configuration is either for cost reasons, or if you needed more power than a triode would provide, but then you have the 211, 845 and GM70 triodes for that. Having said that, you can still get a nice result from a pentode or a beam tetrode.
Thank you for your faintly condescending reply.Well you might want to do some research and look at who makes what in high-end audio to see what tubes they use. I think that should clarify things nicely for you...
But just to confirm it for you, the best performance is achieved with the following configuration.
1. Directly heated Triodes in single-ended configuration.
2. Directly heated Triodes in parallel single-ended configuration
3. Directly heated Triodes in push-pull configuration
4. Indirectly heated Triodes in single-ended configuration
5. Indirectly heated Triodes in parallel single-ended configuration
6. Indirectly heated Triodes in push-pull configuration
7. Pentode/Beam Tetrode in single-ended configuration.
8. Pentode/Beam Tetrode in parallel single-ended configuration
9. Pentode/Beam Tetrode in push-pull configuration
The only reason a pentode or a beam tetrode would be used in a single ended configuration is either for cost reasons, or if you needed more power than a triode would provide, but then you have the 211, 845 and GM70 triodes for that. Having said that, you can still get a nice result from a pentode or a beam tetrode.
Your comment “ “ which is why triodes are the preferred tube of choice for best audio performance “ should have been worded with more clarity and along the lines of your post as above , as to me it clearly insinuated DHT valves.
I take it that in this case 'performance' is an alternative meaning not normally used. You mean 'sonic' performance, not measured performance, I'm guessing, although that too is certainly up for debate (which IME can be quite endless....).Well you might want to do some research and look at who makes what in high-end audio to see what tubes they use. I think that should clarify things nicely for you...
But just to confirm it for you, the best performance is achieved with the following configuration.
1. Directly heated Triodes in single-ended configuration.
2. Directly heated Triodes in parallel single-ended configuration
3. Directly heated Triodes in push-pull configuration
4. Indirectly heated Triodes in single-ended configuration
5. Indirectly heated Triodes in parallel single-ended configuration
6. Indirectly heated Triodes in push-pull configuration
7. Pentode/Beam Tetrode in single-ended configuration.
8. Pentode/Beam Tetrode in parallel single-ended configuration
9. Pentode/Beam Tetrode in push-pull configuration
The only reason a pentode or a beam tetrode would be used in a single ended configuration is either for cost reasons, or if you needed more power than a triode would provide, but then you have the 211, 845 and GM70 triodes for that. Having said that, you can still get a nice result from a pentode or a beam tetrode.
So much depends on topology! For example IME I've noticed that when designing a tube amp the thing to avoid is mixing single-ended circuits with balanced/differential/push-pull circuits. You do one or the other; mixing them does not show off the best traits of either.
But when such things are compared the variables are often profound, and profoundly ignored, like different parts used, vast differences in power, different grounding schemes, different classes of operation, different scales of execution. The latter has such a profound effect that on its own can render the above quote false depending on the amps compared.
I would agree with the statement that triodes are the preferred choice...or some tetrodes and pentodes wired in triode... The 813 used by Aries Cerat is very linear...when wired as a triode.
It is a fact that as an amplifying element, a triode (or a pentode wired in triode) is still the most linear amplification element ever invented.
The 813 beam Tetrode, when wired in triode, is superior in linearity to a 211 or 845 (not sure about GM70 but good examples sound better than most 845/211 amps out there)...it is also direct heated. I would put indirect heated triodes in SE ahead of anything push/pull (there are some VERY good 6C33C amps out there, for example).Well you might want to do some research and look at who makes what in high-end audio to see what tubes they use. I think that should clarify things nicely for you...
But just to confirm it for you, the best performance is achieved with the following configuration.
1. Directly heated Triodes in single-ended configuration.
2. Directly heated Triodes in parallel single-ended configuration
3. Directly heated Triodes in push-pull configuration
4. Indirectly heated Triodes in single-ended configuration
5. Indirectly heated Triodes in parallel single-ended configuration
6. Indirectly heated Triodes in push-pull configuration
7. Pentode/Beam Tetrode in single-ended configuration.
8. Pentode/Beam Tetrode in parallel single-ended configuration
9. Pentode/Beam Tetrode in push-pull configuration
The only reason a pentode or a beam tetrode would be used in a single ended configuration is either for cost reasons, or if you needed more power than a triode would provide, but then you have the 211, 845 and GM70 triodes for that. Having said that, you can still get a nice result from a pentode or a beam tetrode.
I believe your list from 1 to 6 is very accurate but I never heard a pentode/beam tetrode sound better in single ended configuration compared to push pull. IME push pull almost always sounded best for pentodes.Well you might want to do some research and look at who makes what in high-end audio to see what tubes they use. I think that should clarify things nicely for you...
But just to confirm it for you, the best performance is achieved with the following configuration.
1. Directly heated Triodes in single-ended configuration.
2. Directly heated Triodes in parallel single-ended configuration
3. Directly heated Triodes in push-pull configuration
4. Indirectly heated Triodes in single-ended configuration
5. Indirectly heated Triodes in parallel single-ended configuration
6. Indirectly heated Triodes in push-pull configuration
7. Pentode/Beam Tetrode in single-ended configuration.
8. Pentode/Beam Tetrode in parallel single-ended configuration
9. Pentode/Beam Tetrode in push-pull configuration
The only reason a pentode or a beam tetrode would be used in a single ended configuration is either for cost reasons, or if you needed more power than a triode would provide, but then you have the 211, 845 and GM70 triodes for that. Having said that, you can still get a nice result from a pentode or a beam tetrode.
I do/did. It’s called Audiopax Model 88. The earliest mk1 is still the best but the third iteration named after someone I know VERY well is pretty darned close.
While both are the same topology the Mk3s share current better between power tubes, reducing distortion, increasing output power (slightly) and increasing power tube life. The voltage amplifier section has lower distortion and wider bandwidth due to greater differential effect. The power supplies throughout the amp have less noise, reducing IMD. So overall the Mk3s sound smoother and more detailed (owing to lower distortion), have greater authority and less noise. Mk3s do not have a bias control; the meter is only used to balanced the output section to remove DC Offset and is otherwise an active VU meter.
A good 211 based amplifier using original 211/VT4-C's will be very difficult to beat from a sound quality prospective. The 845 and GM70 tubes do not have the delicacy or the subtlety of the 211/VT4-C. However these tubes are good if power is more important than sound quality. If we are considering very high efficiency loudspeakers then the 211 can be beaten with a very good 2A3 or 45 design. Having said that, power will be significantly down on the 211 in SET configuration, so the 2A3/45 design could only be used with horn loudspeakers of 100dB and above efficiency.
Apparently GM70 copper plates can go toe to toe with the 211 in terms of sophistication. I will try some later in one of my amps soon...
Some observation from my experience that might be interesting to you all. I am using balanced differential 300B amps, designed by my late dear friend Allen Wright, to drive mid-range horns using Classic Audio field coil 4" compression drivers. The mid-range has about 112dB/W @ 1M sensitivity. There is only a DC blocking capacitor in-between since I am using an electronic crossover. This means I can hear everything that is going on in those amps. I have noticed the amps becoming more noisy with time. I then figured out that this was due to aging of the coupling caps between the driver stage and the 300Bs. I also experimented with different coupling caps and found that this made a difference. I suspect it might be a difference in the leakage current. The caps have 350VDC on the driver side. The quietest caps I have found (and the best sound to my ears) is the Wima FKP4. Of course, I have not invested in super crazy expensive caps with Teflon etc., but I have tried PIOs as well as other film and foil boutique caps. I used Psvane 300Bs for a while, and when I switched over to Takatsuki 300Bs, the noise went down further. Recently, I bought some of the new WE300Bs, and the noise floor was lower still. Subjectively, I could get the residue noise down to 3mV with the Psvane, about 1.8mV with the Takatsuki, but with the WE, my Fluke meter could not measure it. Neither can I hear it with my ear inside the horn. Incredible. The WE must have a unique cathode structure that is very well balanced.
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