Calling all octal cornet builders, an invitation to post piccies and share experiences building this phono stage especially the scratch builders as I am leaning towards this design to build. Other octal phono designs most welcome infact a definitive octal thread would be great.Lead on McDuff! cheers fergs
I reckon it would be worthwile for you guys to get a custom transformer wound. Since a phono stage can do with extra measures to keep noise out of your phono stage..Such as electrostatic screens between primary and secondary. And then go DC on the filaments with a seperate (maybe surplus) transformer.
I am in the planning stages of building one also. Actually a Claricorn ( Clarinet and Cornet 2 ) in the same chassis with one power supply for both. I am also leaning towards wiring PTP instead of using the boards and building the Cornet side as a hybrid, ( miniature/octal ). I'm trying to keep the costs low. I have the power transformer already and I think I can source the rest of the parts for around $150.00 without the tubes and chassis. I will make the chassis myself. I would be very interested in pics and comments from others that have gone this route also.
Mark
Mark
Hi Guys,
You can try Voller transformers in Highett. Paul is great to work with and his transformers are reasonably priced. Turn around time is also quick. I got a surplus transformer from him for my cornet project, so also check if he has any lying around. There is also ses transformers in Dandenong:
http://www.southernelectronicservices.com.au/home.htm
In my cornet I have used a 12BH7 and 6n6p for the output tubes. I'll try the 6sn7 or even a pair 7193's at some stage. The 12BH7 is easy to implement since it's a noval and if you're using a ccs on the cathode it's easy to change the current set resistor and use a 12AU7 or 12BH7. The heater connection was different for the 6n6p and its use also resulted in a hum, so I went with the 12BH7.
What I'm doing now is building the power supply separate to circuit boards and adding in a choke.
Cheers,
Rich
You can try Voller transformers in Highett. Paul is great to work with and his transformers are reasonably priced. Turn around time is also quick. I got a surplus transformer from him for my cornet project, so also check if he has any lying around. There is also ses transformers in Dandenong:
http://www.southernelectronicservices.com.au/home.htm
In my cornet I have used a 12BH7 and 6n6p for the output tubes. I'll try the 6sn7 or even a pair 7193's at some stage. The 12BH7 is easy to implement since it's a noval and if you're using a ccs on the cathode it's easy to change the current set resistor and use a 12AU7 or 12BH7. The heater connection was different for the 6n6p and its use also resulted in a hum, so I went with the 12BH7.
What I'm doing now is building the power supply separate to circuit boards and adding in a choke.
Cheers,
Rich
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Please excuse the intrusion. But I`m fascinated by this and the fact that at least one of these variations unashamedly uses the 7025 tube (which is a 12AX7 variant) and 6sn7.
I keep hearing the 7025 (12AX7) is such a poor tube for phono stage designs and yet here it is used again. I posited the use of 6sn7s as well in another thread and was met by deafening silence...so your opinions please regarding this topology.
I keep hearing the 7025 (12AX7) is such a poor tube for phono stage designs and yet here it is used again. I posited the use of 6sn7s as well in another thread and was met by deafening silence...so your opinions please regarding this topology.
7025
This is what Hagerman says about the Octal "hybrid" version of Cornet, hybrid in that it uses an octal 6SN7 cathode follower and 9-pin 12AX7's for gain:
He's the engineer who's responsible for the design of this preamp - as well as several other very well-regarded designs- and if he says he likes using the 12AX7 in this design, I'll go with his expertise over opinions of people whose engineering pedigree is unknown to me.
The 7025 is a low noise / low microphonics version of the 12AX7. It is otherwise identical.
This is what Hagerman says about the Octal "hybrid" version of Cornet, hybrid in that it uses an octal 6SN7 cathode follower and 9-pin 12AX7's for gain:
I think the 6SN7 makes the best cathode follower. More current, better linearity, better voltage ratings. I like the tube. I also like the 12AX7 for high gain amplification.
Keep in mind, a LOT of the sound has to do with topology and circuit design, not just tubes. I can make no claim that octals are superior to novals, nor the other way around. Each tube has to stand on its own merits.
Keep in mind, a LOT of the sound has to do with topology and circuit design, not just tubes. I can make no claim that octals are superior to novals, nor the other way around. Each tube has to stand on its own merits.
He's the engineer who's responsible for the design of this preamp - as well as several other very well-regarded designs- and if he says he likes using the 12AX7 in this design, I'll go with his expertise over opinions of people whose engineering pedigree is unknown to me.
The 7025 is a low noise / low microphonics version of the 12AX7. It is otherwise identical.
good 6SN7 is almost lab tube, but has to be supplied with very high Anode voltage
(even higher PS voltage...) Lets say more than 300 of Va around -13V Ug and cca 10mA
to give awesome results. extremely linear...
Please take a look at the datas
Just little bit higher capacitances but there is no problem, just put the right value of input R or pot
which is 25K (22K) or less. persuming the stage before is low impedance source.
cheers
(even higher PS voltage...) Lets say more than 300 of Va around -13V Ug and cca 10mA
to give awesome results. extremely linear...
Please take a look at the datas
Just little bit higher capacitances but there is no problem, just put the right value of input R or pot
which is 25K (22K) or less. persuming the stage before is low impedance source.
cheers
People are going to love me for opening up this antique thread but I just had to.
I seem to file away all the interesting schematics that I would like to build at some time or another and I got to thinking about the Octal Cornet Phono preamp and I think I want to try my hand at it. Note, It will be my first phono preamp.
Anyway I dug up an old schematic but I don't see the B+ voltage so I'm going to assume its around 380VDC? Is this correct?
Also it looks like the first two stages are running about 2mA each and the final at 14mA?
Please do correct me if I am mistaken. I would like to obtain the grid, plate and cathode voltages if I could before I set forth to make it.
I seem to file away all the interesting schematics that I would like to build at some time or another and I got to thinking about the Octal Cornet Phono preamp and I think I want to try my hand at it. Note, It will be my first phono preamp.
Anyway I dug up an old schematic but I don't see the B+ voltage so I'm going to assume its around 380VDC? Is this correct?
Also it looks like the first two stages are running about 2mA each and the final at 14mA?
Please do correct me if I am mistaken. I would like to obtain the grid, plate and cathode voltages if I could before I set forth to make it.
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