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Input Tube Selection for Amplifier
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Author:  rock4016 [ June 4th, 2013, 12:30 pm ]
Post subject:  Re: Input Tube Selection for Amplifier
Grover used a 6N7 as an input tube for multiple amps, I'm sure he could provide some good info.
Author:  High Transconductance [ June 4th, 2013, 12:41 pm ]
Post subject:  Re: Input Tube Selection for Amplifier
Administrator/Moderator/Almighty one, is Grover subscribed here?
Author:  Roscoe Primrose [ June 4th, 2013, 1:21 pm ]
Post subject:  Re: Input Tube Selection for Amplifier
High Transconductance wrote:
Administrator/Moderator/Almighty one, is Grover subscribed here?


Not to the best of my knowledge...

Roscoe
Author:  Grover Gardner [ June 4th, 2013, 2:58 pm ]
Post subject:  Re: Input Tube Selection for Amplifier
Okay, here we go! Thanks, Roscoe.

Parallel 6N7 is a great tube, gain of 35, Rp around 22K I think. Very musical. Check out Thomas Mayer's blog:

http://vinylsavor.blogspot.com

He has a "Tube of the Month" feature and some of these are inexpensive high-gain tubes that have been overlooked by the hobbyists. You might find something you like there.
Author:  Grover Gardner [ June 4th, 2013, 3:32 pm ]
Post subject:  Re: Input Tube Selection for Amplifier
Oh, as for the 6N7 as a differential amp, it's great. Again, gain of around 35. Don't know the Rp for the individual sections. There is a well-known vintage amp that used this as a differential phase splitter but I can't recall which one it was. I think you would typically use about 47K plate load per section running at bout 3 ma each.
Author:  FerdinandII [ June 4th, 2013, 8:47 pm ]
Post subject:  Re: Input Tube Selection for Amplifier
High Transconductance wrote:
Interesting. Any idea where to find curves and Cg-p data? I only found a listing as a Class B amplifier. I may even have some. Did I mention I like octal? :D


It's the same as 6A6 and 53, electrically.

Here's a Tong-Sol data sheet for the 6A6, courtesy of Frank's Electron tube Pages:

http://tubedata.tubes.se/sheets/127/6/6A6.pdf

OK, sorry, that one's for Power Duty, not small-signal use.
Here's the set of curves we're looking for....

http://tubedata.tubes.se/sheets/021/6/6A6.pdf
Author:  Grover Gardner [ June 5th, 2013, 3:14 am ]
Post subject:  Re: Input Tube Selection for Amplifier
Oh, excellent, thanks!
Author:  FerdinandII [ June 17th, 2013, 12:29 pm ]
Post subject:  Re: Input Tube Selection for Amplifier
How about a 1633 as a replacement for one of the 6SN7s? It's a special grade with tightly matched sections.
It's for military radios, so it has a 25V heater, but otherwise it's just a 6SN7 with matched sections.
Yes it's Octal.... :roll:
Yes, you can borrow a couple if you want to test them.... :clap:

http://frank.pocnet.net/sheets/049/1/1631.pdf
Author:  Guy [ June 17th, 2013, 2:20 pm ]
Post subject:  Re: Input Tube Selection for Amplifier
FerdinandII,

Interesting choice - I've not heard about that one! Let me stir it into the mix and see what drops out. The heater doesn't throw me. As you say, it looks like another 6SN7/6J7 but with a difference heater requirement. It also looks like the plate ti reduced to 300V from 450V, and plate dissipation drops from 7.5W to 2.5W. Grid-to-Plate capacitance is a little lower, and you say the sections are better matched. Let's see if I can determine how much head room I have with these.
Author:  FerdinandII [ June 17th, 2013, 2:53 pm ]
Post subject:  Re: Input Tube Selection for Amplifier
Guy,

Sorry for any confusion, but I meant to recommend it to Stuart, since he's gone all DIFF AMP on me...... :lolno:

Nothing that would prevent you from using it, but NOS choice is limited and they can be pricey.


Guy wrote:
FerdinandII,

Interesting choice - I've not heard about that one! Let me stir it into the mix and see what drops out. The heater doesn't throw me. As you say, it looks like another 6SN7/6J7 but with a difference heater requirement. It also looks like the plate ti reduced to 300V from 450V, and plate dissipation drops from 7.5W to 2.5W. Grid-to-Plate capacitance is a little lower, and you say the sections are better matched. Let's see if I can determine how much head room I have with these.
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