Low distortion? minimun or medium
Single Ended? yes
10 Watts? 6 o 7 usable.
6L6G or EL34? both
Willing to use a higher wattage tube, or to parallel two of the above tubes to get the power with SE? could be higher wattage tube
Less than 10 Watts would be OK? yes
Push Pull with 6L6G or EL34; i prefer single ended
or with other tubes, EL84, or etc.? i dont know
Single Ended? yes
10 Watts? 6 o 7 usable.
6L6G or EL34? both
Willing to use a higher wattage tube, or to parallel two of the above tubes to get the power with SE? could be higher wattage tube
Less than 10 Watts would be OK? yes
Push Pull with 6L6G or EL34; i prefer single ended
or with other tubes, EL84, or etc.? i dont know
You can get 10W out of a good quality EL34 (truly selected for strong emission and gm). A bit less from the 6L6. I do prefer the EL34 but it's just personal preference. The difference between 8W and 10W is academic in real use......you find out on the bench and then forget about it.
I used 3.3K/8R output transformer that gave good power delivery in the 6-10R range which is typical for a well behaved loudspeaker. Max power was >10W into 6R with 3% THD. Feedback 16 dB.
Nominal output power into nominal 8R was about 9W with just 1% THD.
The EL34 worked at 300V plate voltage, 250V g2 voltage (both SS regulated) and 80 mA anode current. Distortion at 1W was about 0.2%...
To get these number with a 300B, first you need to run it HOTTER than 24W (which means useful life might be limited), need to use a REALLY good 300B and the driver will be quite more complicated because of the low gain of the 300B. In few words it WILL be a lot more expensive because it's not just the cost of the tubes.
With the EL34 in pentode mode a good 12AX7/ECC83 will be fine......for a power amp with about 1.4V rms sensitivity (for full output power). You can invest more money in a good quality output transformer with large bandwidth, good inductance and power handling....
With a good and proper speaker the amp sounds nicely. Do not trust generic comments about sound. They are meaningless, IMHO.
I used 3.3K/8R output transformer that gave good power delivery in the 6-10R range which is typical for a well behaved loudspeaker. Max power was >10W into 6R with 3% THD. Feedback 16 dB.
Nominal output power into nominal 8R was about 9W with just 1% THD.
The EL34 worked at 300V plate voltage, 250V g2 voltage (both SS regulated) and 80 mA anode current. Distortion at 1W was about 0.2%...
To get these number with a 300B, first you need to run it HOTTER than 24W (which means useful life might be limited), need to use a REALLY good 300B and the driver will be quite more complicated because of the low gain of the 300B. In few words it WILL be a lot more expensive because it's not just the cost of the tubes.
With the EL34 in pentode mode a good 12AX7/ECC83 will be fine......for a power amp with about 1.4V rms sensitivity (for full output power). You can invest more money in a good quality output transformer with large bandwidth, good inductance and power handling....
With a good and proper speaker the amp sounds nicely. Do not trust generic comments about sound. They are meaningless, IMHO.
If you want to do it triode, the 6CB5A is cheap tube.
Check out this link: VinylSavor: Single Ended Amplifier Concept, Part 4
My version of that amplifier is here: http://6streetbridge.blogspot.com/2013/04/building-single-ended-6cb5a-amplifier.html
For single ended pentode - EL34, KT88, EL156, etc can be used. I built a "Universal" single-ended amplifier using fixed bias so I could try different tubes. Loop or plate-to-plate feedback would be needed to keep distortion low and provide damping. It is a different sound - subjectively speaking - faster and tighter bass.
Something like this: http://6streetbridge.blogspot.com/2013/11/project-mult-valve-universal-pentode.html
Check out this link: VinylSavor: Single Ended Amplifier Concept, Part 4
My version of that amplifier is here: http://6streetbridge.blogspot.com/2013/04/building-single-ended-6cb5a-amplifier.html
For single ended pentode - EL34, KT88, EL156, etc can be used. I built a "Universal" single-ended amplifier using fixed bias so I could try different tubes. Loop or plate-to-plate feedback would be needed to keep distortion low and provide damping. It is a different sound - subjectively speaking - faster and tighter bass.
Something like this: http://6streetbridge.blogspot.com/2013/11/project-mult-valve-universal-pentode.html
811a amps are not for beginners; takes weeks to hand punch the chassis. many hours to wire point to point. |The amps I built are very quiet even on 105 Db speakers. One friend has used his for 22 years after 20 years the Russian 811A where still within specs, but my friend prefers the Chinese 5725B which hAVE SHORT LIVES.
Quite some bold statements, aren't they? I'm sure you want to substantiate them
Best regards!
Cheap understanding of electronics demand expensive components, it is true. Like, expensive knowledge of electronics allows to get great results from cheap components, that's the forum is for. We are constantly discussing here how to get great sound quality. People who can learn, get it finally, using unexpensive parts. People who can't learn from the wisdom of people on this forum, are doomed to buy expensive tubes, transformers, capacitors, and even power cables.......
multi,
"Paralleling Tubes Effects" was the cover article in Glass Audio, Volume 12, Number 5, year 2000.
This was the last issue of Glass Audio, before 3 Ed Dell publications were combined into one magazine.
I can hardly believe we did the research starting in 1998 and ending in 2000, such a long time ago.
Then I presented the essence of the article at VSAC 2003. At VSAC 2008 I did a presentation and then a listening demo of
a parallel 300B amp and a push pull 300B amp, with the same currents in the outputs, and the 300B tubes all seeing the same load impedance. A null method was used to balance the gain precisely, and then the music was switched from PSE to PP and back again.
I have talked about this more than once on threads in diyAudio.
"Paralleling Tubes Effects" was the cover article in Glass Audio, Volume 12, Number 5, year 2000.
This was the last issue of Glass Audio, before 3 Ed Dell publications were combined into one magazine.
I can hardly believe we did the research starting in 1998 and ending in 2000, such a long time ago.
Then I presented the essence of the article at VSAC 2003. At VSAC 2008 I did a presentation and then a listening demo of
a parallel 300B amp and a push pull 300B amp, with the same currents in the outputs, and the 300B tubes all seeing the same load impedance. A null method was used to balance the gain precisely, and then the music was switched from PSE to PP and back again.
I have talked about this more than once on threads in diyAudio.
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Well said, Wave. There are so many...tells, and give aways.. posted. It's get tough to engage and help someone who has a problem after installing a $50 coupling cap.
Judging by your words, do you have a theory about the size of a transformer and is a big transformer always better in it? I always thought that the transformer was calculated on the optimal size in order to fulfill the compromise requirements, and not just surprise the neighbor.
4П1Л 7.5W anode power, do you compare its price with 300B, but do not compare with 811A? Very funny ...
4П1Л 7.5W anode power, do you compare its price with 300B, but do not compare with 811A? Very funny ...
About the price of the transformer. A large transformer can even be cheaper if it uses cheap and low-grade silicon steel. Therefore, it is difficult to judge the actual quality of a transformer only by its size.
If we compare pentodes with indirect heat, for example, the GU50 and EL34, then 1) The GU50 is five times cheaper! 2) The anode power of the GU50 is about 15W more. 3) And the voltage at the anode can be 900V and 3000V peak! In terms of sound quality, they are roughly comparable because EL34 is also not a masterpiece. For those who do not know, in contrast to EL34 GU50, this is already a beam pentode, and this is a clone of the LS50 Telefunken 1940 - 1945.
LS 50, Tube LS50; Rohre LS 50 ID2528, Vacuum Pentode
If we compare pentodes with indirect heat, for example, the GU50 and EL34, then 1) The GU50 is five times cheaper! 2) The anode power of the GU50 is about 15W more. 3) And the voltage at the anode can be 900V and 3000V peak! In terms of sound quality, they are roughly comparable because EL34 is also not a masterpiece. For those who do not know, in contrast to EL34 GU50, this is already a beam pentode, and this is a clone of the LS50 Telefunken 1940 - 1945.
LS 50, Tube LS50; Rohre LS 50 ID2528, Vacuum Pentode
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No, no, no! The Telefunken LS 50 was a true pentode with a helicoidal suppressor grid, as were all her successors.
Best regards!
So in the USSR something better copied. According to the design of the cylinder and the anode, voltage of 12V and other parameters, this is a clone, and for its intended purpose it is also a tube for military radio stations in the first place. They were made a lot, and therefore the prices are very low, and not because they are of poor quality. And according to the datasheet, it can be done with the right characteristic, such as 811A, if you include all the grids together, but the heat will remain indirect. This tube is very reliable and economical in terms of heat for tubes with indirect heating and 40 W power at the anode. Although probably there were even more economical in terms of power filament.
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While it is true that theory does not always line up with reality, I would be very cautious about dismissing it.
An SE amp with parallel 6L6GCs could sound excellent, provided that you wrap some negative feedback around it to get the output impedance down. In this case, decent transformers is necessary so as to 1) have sufficient magnetic headroom, and 2) Have a decent high-frequency response so as to allow more feedback without oscillation issues.
At least for me, the OPT is the single biggest wild card when it comes to designing a NFB loop on paper. They aren't always consistent.
One of the best (and most consistent sounding) amps I've tried is an MC^2 MC650- 650 WPC solid state amplifier that exhibits THD numbers down around .005%. It's about as clean and low-distortion as you can get. Is it better or worse than a tube amp? Not necessarily. But my point is that low-distortion amps with a lot of feedback aren't inherently bad.
Ramble over.
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