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In Reply to: RE: Advice on getting a 45 built posted by TAdams on December 16, 2014 at 09:23:13
Hey TAdams,
Just a couple of questions and observations:
1. Is this your first build? If yes, please do a web search on safe practices..can't enjoy your work if you're lying dead in a puddle of piss.
2. keep it simple. A DC couple amp with multiple inputs and the ability to drive a load like headphones for a first build is a bit ambitious. Others on the forum might encourage you...obviously your choice.
3. There are simple RC or IT coupled designs out there that will let the magic out. I found Parafeed fairly simple to implement with a little tweaking of the cap. You can achieve a good sounding quiet design and leave room for more complexity in the future.
4. Prototype the amp on a board. Just keep kids and pets away.
5. After you're happy with the prototype, move to chassis and follow good mounting an grounding practices...just search this forum. Then you work on a quiet build.
6. A good middle of the road OPT that I like is Lundahl SE LL1663 5K primaries gapped for 50mA will do nicely. Around $350.00 for a pair. They are C core and ugly, but good sounding. You will want to hide them...
7. With 2 glorious watts to work with, your speaker drivers will need to be at least 98db/watt efficient. You can go less efficient in a crutch. You will loose much of the magic though...
Good luck...use this forum, ignore the bickering..many of our members are suffering from low "T" and tend to bicker like women...;>)
Stuben
Follow Ups:
Hi Stuben
I don't build amps so I am having someone build this for me. I have someone in mind but if anyone wants to put their name in the hat then right on.
Cheers~
If you are having this built on spec, you will get what you asked for. It may or may-not sound good. It seems to me that you need to audition some amp designs and then decide which is for you and then have it built. The volume pot and selector switches are just add-ons and no real problem for a builder.
In my experience, the output xfmr and gain/driver tubes are the most important considerations to the design. Nickel core outputs are the best IMO. Early radio tubes, 37, 76, 6C5, 6C6, 6F8 ... are my favorites for gain/driver, 6SN7 and 6SL7 are also good.
Consider contacting Dave Slagle for nickel outputs. He is a member here, and he is also a friend ( to be upfront about it ) and an avid builder.
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."
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.
Well This is the SET forum and not the DIY...My bad.
Many say the DC coupled amps are quite magical..
Check out Paul Joppa's thread on the DC coupled 2a3. Very generous guy...
Stuben
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