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In Reply to: RE: Advice on getting a 45 built posted by hifipaul on December 17, 2014 at 06:36:15
Thanks for the input Gents I really appreciate it.
Hifi Paul: I agree I should do some auditioning. I live in Edmonton Canada. Any SET heads around here? Perhaps I should do a separate post inquiring. I also would not like to go on spec but have someone who will tweak a circuit to something special.
Frihed & Amioulatine: I am getting more interested in the Simple 45 parafeed with Magnaquest iron. In particular I read Bill Epstein's article on the build he did in conjunction with Steve Brown in 07. So unless there are any major objections I think this is where the journey will lead off to at this point. Are Steve and Bill still around for input?
http://dagogo.com/the-simple-45
http://www.positive-feedback.com/Issue1/single.htm
http://www.audioasylum.com/cgi/t.mpl?f=magnequest&m=5599
"The unparalleled linearity of the 45 tube (1930’s National Union) together with the bandwidth of Mike Lefevre’s Robin Hood transformers and a touch of romance from Brian Cherry’s Obbligato oil caps combined to bring a life to all the music we played like I have seldom heard."
Follow Ups:
I think the simple 45 with Magnequest output transformer is a great place to start and a very simple project for the builder. I would use a K & K CCS on the first tube and a Magnequest DS 050 for the output transformer. The first tube can be any of the 12AT7/12AV7/6N1P varients (like the 5965). Don't forget that with 2V coming from the CD player or phono stage and a bias voltage of -56V you only need a gain of 28 to drive the amp to clipping. If we add 3dB for headroom, you still only need a gain of <40 to drive the amp to clipping. That's not much of a challenge.Don't get bogged down in audio dogma. Keep it simple and worry about boutique parts later. Those are things you can change or experiment with yourself once the amp in built. If you start with an excellent output transformer and a chassis with plenty of space, you can mess with it for years.
Edits: 12/17/14
I use a cd player to a Grant Fidelity Tube Dac 11. Using the tube buffer and volume control it's 2V and using the straight dac out with no volume control (and more transparent) it's 6V so I guess I should take this in to consideration as well? Down the road I might get a new dac but that won't happen for years or unless it fails.
Yes, the Grant Fidelity Tube Dac 11 documentation leaves a lot to be desired, but it appears as if the "DAC out" is line level, e.g. 2V and the the tube "buffer" and volume control with the added gain stage of the tube has an output of 6V. That said, I think you will find the best sound if you put the volume control (100k audio taper) on the front of the amp and use the DAC line out. 2VRMS line output is the standard "Red Book" value so you don't need to worry about future CD player or DAC purchases.
I build all my amps with an expected 2V RMS input, so I actually try to have the amp clip with a 1V input to give myself 6dB of headroom, but it is not always possible to achieve this with a two stage amp which is what you are considering. As I stated above, with 2V into your volume control and the 45 tube clipping with 56V at the grid, it should be simple to engineer a two stage amp.
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