I don't mind people making their own EL84 Amp as long as it's not for commercial reasons; I believe in sharing information. I used an EL84 in triode mode because it was the biggest tube I had in the box at the time. That kind of parallel feed coupling is just about the least efficient way of transferring power, so I needed a beefy tube to get a decent output. This is the original post:-
http://groupdiy.com/index.php?topic=42991.msg535231#msg535231
V1 gain 28, V2 gain 12.7, transformers cancel. Overall gain 51dB
I agree about the Beatles gear, I guess people regard it as some kind of safe benchmark. I think the point about the REDD47 being an English V72 is a good one, DC and AC feedback, only thing missing is the choke. EMI probably thought, why not make our own rather than paying for German gear.
Regarding Negative feedback, I believe Harold Stephen Black (of Bell labs) came up with the idea in 1927, but did not publish until 1934. In the days before the internet, ideas moved slowly, especially revolutionary ones that were tricky to incorporate. I think the development did not really take-off until after the war, when a lot of forces trained guys were keen to use new ideas. I think 6-10dB does little harm, but to use it wholesale to correct bad design is a mistake in my opinion. Its much the same situation with computer programming, to put it into a modern context. In the days before massive memory and storage, programs were very efficient, now because memory and storage is no longer an issue we have bloated programs, just look at how big the updates are getting. Before feedback guys had to work hard to find sweet spots where tubes performed best.
Sowter make a good 7:1 for the REDD47 I believe, I used their 4:1 versions because I did not need a 200 ohm system. That is another point, all their gear was 200 ohms in and out which must have affected the sound a little too. This is what I mean about ideas travelling slowly, Bell labs came up with the 600 ohm standard in 1942 but Abbey road was still using 200 ohms 20 years later!
best
DaveP
http://groupdiy.com/index.php?topic=42991.msg535231#msg535231
V1 gain 28, V2 gain 12.7, transformers cancel. Overall gain 51dB
I agree about the Beatles gear, I guess people regard it as some kind of safe benchmark. I think the point about the REDD47 being an English V72 is a good one, DC and AC feedback, only thing missing is the choke. EMI probably thought, why not make our own rather than paying for German gear.
Regarding Negative feedback, I believe Harold Stephen Black (of Bell labs) came up with the idea in 1927, but did not publish until 1934. In the days before the internet, ideas moved slowly, especially revolutionary ones that were tricky to incorporate. I think the development did not really take-off until after the war, when a lot of forces trained guys were keen to use new ideas. I think 6-10dB does little harm, but to use it wholesale to correct bad design is a mistake in my opinion. Its much the same situation with computer programming, to put it into a modern context. In the days before massive memory and storage, programs were very efficient, now because memory and storage is no longer an issue we have bloated programs, just look at how big the updates are getting. Before feedback guys had to work hard to find sweet spots where tubes performed best.
Sowter make a good 7:1 for the REDD47 I believe, I used their 4:1 versions because I did not need a 200 ohm system. That is another point, all their gear was 200 ohms in and out which must have affected the sound a little too. This is what I mean about ideas travelling slowly, Bell labs came up with the 600 ohm standard in 1942 but Abbey road was still using 200 ohms 20 years later!
best
DaveP
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