Hi guys, thanks for all the input till now. Sorry I didn't reply earlier but I am in different time zone; I went to bed 3AM this morning, after exchanging threads with you...
Elli, you are correct, those heads are low impedance, their resistance is 20 Ohms / 2.5mH for PB head and 17 Ohms / 4mH for record head. Actualy, I bought brand new Nortronics Rec. and PB heads few years ago, directly from Joe Dundovich, who was owner of Nortronics in 70's, was selling his old stock till recently under Magnetic Head Company. Not in business any more, and his stock was bought by Flux Magnetics. Aperently they are better then original Ampex...
After reading some papers on Cascode ampllifiers I am inclined to belive that it could be the right aproach for the project to acheive the minimum noise Though informations were about using transistors, not tubes. I had two tubes in mind: D3a and Philips 6021. The second one in particular look interesting to me bacause of it's miniature size, and it is described as audio tube. Did anyone had experience with any of the tubes?
I have attached diagrams of PB, Record and Bias amps.
Elli, you are correct, those heads are low impedance, their resistance is 20 Ohms / 2.5mH for PB head and 17 Ohms / 4mH for record head. Actualy, I bought brand new Nortronics Rec. and PB heads few years ago, directly from Joe Dundovich, who was owner of Nortronics in 70's, was selling his old stock till recently under Magnetic Head Company. Not in business any more, and his stock was bought by Flux Magnetics. Aperently they are better then original Ampex...
After reading some papers on Cascode ampllifiers I am inclined to belive that it could be the right aproach for the project to acheive the minimum noise Though informations were about using transistors, not tubes. I had two tubes in mind: D3a and Philips 6021. The second one in particular look interesting to me bacause of it's miniature size, and it is described as audio tube. Did anyone had experience with any of the tubes?
I have attached diagrams of PB, Record and Bias amps.
Attachments
The MM1200 is a 16 track machine. That is a large number of amps to construct. I would not attempt it with a multritrack. If you want a tube sound, why not seek out an MR70 Ampex (nuvistor) or Studer C or J 37. Both are all tubes, but only 4 tracks on the J37 and 2 tracks on the others. Regards
I am looking into geting Studer C37 (if can find one) as mastering recorder. Ampex MX70 does not have enough channels and is using 1/4" tape where crosstalk can be a problem. My MM-1200 is 8 channel machine, reasonable number, and is using 1" tape, making it very good choice from channel crosstalk point of view.
There is another interesting tube that can be used - ECC86, interesting as it can be used with 12 or 24V...
There is another interesting tube that can be used - ECC86, interesting as it can be used with 12 or 24V...
The ECC86/6GM8 doesn't have enough gain and it's becoming scarce.
The problem of handling mag. tape playback and mag. cart. playback of records is identical, save for different time constants in the EQ network. I strongly suggest you check Allen Wright's hybrid cascode circuits out. Sadly, AW is no longer with us, but fellow "Aussie" Joe Rasmussen should be able to provide some assistance.
The problem of handling mag. tape playback and mag. cart. playback of records is identical, save for different time constants in the EQ network. I strongly suggest you check Allen Wright's hybrid cascode circuits out. Sadly, AW is no longer with us, but fellow "Aussie" Joe Rasmussen should be able to provide some assistance.
No need for transistor cascode, microphone input transformers for tube gear can be used here. Like 600 Ohm CT : 40 KOhm. For input stage I would recommend 6S17K-V planar triode, it is the best tube I know for sensitive input stages. I use such combinations in microphone preamps, they are deadly silent.
Thank you Wavebourn, I will take you suggestion in consideration; never heared of that one, but something very silent would definitely be appreaciated as input for recording stage...
Here is the service manual of Revox G36. It contains the schematic as well.
Revox G36 has separate recording and playback tube amplifiers of quite high grade.
http://www.johnmcculloch.net/docs/g36Manual.pdf
Revox G36 has separate recording and playback tube amplifiers of quite high grade.
http://www.johnmcculloch.net/docs/g36Manual.pdf
Thank you for your contribution to discussion Artisalo; first for the manual of G36 directly, which, indirectly then led me to something that I didnt expect (and know). I searched about ECC83 (used in G36) on the net, what took me to this wonderful site of JAC-music (ECC803S TESLA FAKE TUBES run by Ing. Jac van de Walle, from Germany. As I was thinking to get some tubes from e-Bay, it (article) came at the right time to point to some traps set by unscrupulous profit makers. Thanks again...
For ECC83 replacement search soviet made 6N2P-EV from ebay.
It is very similar to ECC83 but it has lower input capacitance - especially Cag - and therefore it suits for this sort of application even better that ECC83.
And the price is much lower.
I have built several phono amplifiers with 6N2P-EV tubes and the results are very good.
It is very similar to ECC83 but it has lower input capacitance - especially Cag - and therefore it suits for this sort of application even better that ECC83.
And the price is much lower.
I have built several phono amplifiers with 6N2P-EV tubes and the results are very good.
Yup, he does. We have custom heads from Flux Magnetics on both 1" 2 track mastering machines. Paul's 1" ATR-100 uses custom tube repro and record electronics from Tim de Paravicini, and his modified MM-1200 1" 2 track uses MR70 record and repro electronics modded by Tim. There is also an ATR-100 in 1/2" 2 track in the herd, that uses the no longer available ATR Services tube record and repro electronics. Our 1/4" slaves do use the stock solid state record circuitry, but it's been modified quite a bit.
Regarding low impedance heads, you can try step up transformers, but I never had much luck with them. Probably easier to have higher impedance heads made. I get asked every once in a while for record electronics to go with our repro amps. If the idea gains enough inertia I will probably give it a whack.
I have a Studer A-80 1/2 inch that has both 4 track and 2 track headstacks. It would be interesting to look into custom heads for the 2 track. How does that work? Do they need a stock head to modify or do they make them from scratch?
I recall the phrase "creative squashing". What is the advantage of vacuum tubes in the record amp, from your perspective (or Paul's)?
Thanks,
Michael
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