If you need really low input capacitance you could consider a cascode input stage with tubes or hybrid fet/tube.
I did a couple of cascode designs which are in the analogue source forum which I and a few others have found generally satisfactory.
I even experimented with the 6J9P (Russian) pentode connected and while SNR was extremely satisfactory there was something about the sound no matter what I tried that I found off putting.
Ketje is dead on the money IME about the EF86, not a tube I would recommend in a modern phono stage design.
Depending on cartridge type you may be able to get away with a triode front end, but I have found miller capacitance to be an issue with all except the lowest impedance MC type cartridges, get good gain out of the first stage for good noise performance and you end up with a lot of input capacitance due to miller capacitance. Using a differential input stage (LTP) does give you a means of canceling input capacitance (think neutralization, i.e. cross connected plate to grid caps) but will give you a 3dB hit on noise - choose a quiet enough tube and this might be a good trade off.
I did a couple of cascode designs which are in the analogue source forum which I and a few others have found generally satisfactory.
I even experimented with the 6J9P (Russian) pentode connected and while SNR was extremely satisfactory there was something about the sound no matter what I tried that I found off putting.
Ketje is dead on the money IME about the EF86, not a tube I would recommend in a modern phono stage design.
Depending on cartridge type you may be able to get away with a triode front end, but I have found miller capacitance to be an issue with all except the lowest impedance MC type cartridges, get good gain out of the first stage for good noise performance and you end up with a lot of input capacitance due to miller capacitance. Using a differential input stage (LTP) does give you a means of canceling input capacitance (think neutralization, i.e. cross connected plate to grid caps) but will give you a 3dB hit on noise - choose a quiet enough tube and this might be a good trade off.
Simply because many types are still being produced in Russia. Also, Russian NOS tends to be much more affordable than W. European NOS.
They're comparably good tubes and cost about 5 - 10% of what similar German tubes cost.
Almost none of the Russian types I prefer are currently in production and most haven't been since about the end of the USSR. There are a few good ones still being made however.
I'm going to send a few trial balloons up.
A possibility for incorporating the EF86 in a phono preamp is to use a CCS loaded 6922 section in the 1st gain block and an EF86 in the 2nd gain block. I think that combination will dispose of the CMiller and S/N ratio issues. As the EF86 is a complete wimp, a DC coupled voltage follower is needed to buffer the O/P.
The 6AC7 is a possibility for a pentode 1st gain block in a phono preamp. A 9 mA./V. gm should not be sneered at. Definitely regulate g2 B+.
A possibility for incorporating the EF86 in a phono preamp is to use a CCS loaded 6922 section in the 1st gain block and an EF86 in the 2nd gain block. I think that combination will dispose of the CMiller and S/N ratio issues. As the EF86 is a complete wimp, a DC coupled voltage follower is needed to buffer the O/P.
The 6AC7 is a possibility for a pentode 1st gain block in a phono preamp. A 9 mA./V. gm should not be sneered at. Definitely regulate g2 B+.
A neat way to use a pentode without the noise problems is to use it as a triode, but: ground the anode and use the screen grid as the anode instead. This minimises Cmiller and provides excellent internal shielding. You can get a gain of about 30dB and Cmiller below 90pF using an EF86 this way.
6C4C is 150$ like rca 2a3 !!!!more than us 6b4g
An externally hosted image should be here but it was not working when we last tested it.
Thank you. Very interest approach.
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After some browsing I read a lot of interesting about D3A/7721 tube. But D3A not easy to find.
6C4C (NOS, NIB, November 1958) was 15 USD
(21-JULY-2013)
/link in Russian/
http://diyaudio.pp.ua/viewtopic.php?t=5459&p=24446
Now you can buy pair of tubes (NOS, NIB, 1984). 15 US for each
/link in Russian/
http://kharkov.kha.olx.ua/uk/obyavlenie/prodam-paru-radiolamp-6s4s-IDaCEvJ.html
(21-JULY-2013)
/link in Russian/
http://diyaudio.pp.ua/viewtopic.php?t=5459&p=24446
Now you can buy pair of tubes (NOS, NIB, 1984). 15 US for each
/link in Russian/
http://kharkov.kha.olx.ua/uk/obyavlenie/prodam-paru-radiolamp-6s4s-IDaCEvJ.html
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I didn't say that was one of the tubes I liked and you didn't ask me which ones I do. A dht power tube as an example in a thread discussing a phono pre-amp is hardly fair. Lol
How about a pair of GM70 for $100? Least as good performing as an 845 IMLE.. (20 - 50W in SE depending on implementation)
6J9P
6J51P
6J52P
6S3P
6S4P
6N14P
6N32P
6N6P
VS for example
5842
417A
7721/D3A
7788/E810F
ECC84
ECC88/6DJ8
5687
Note that I would not necessarily use all of these in identical applications but they are ones I am familiar with.
The 6J52P is a cheap alternative, and they are indeed very quiet. But beware that those super-high-gm pentodes are usually very microphonic, have punishing Cmiller, and you rarely get a matched pair out of the box.
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