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Old 29th August 2012, 08:47 PM   #1
castorG is offline castorG  Italy
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Default 45 tube amp schematic

Hi everyone,
I'm looking for a good 45 tube amp schematic. I need it as simple as possible (so I can spend more on the single pieces), but with a high-end sound since it will stay with me for a long time to come. I'm thinking on using emission labs tubes, those with an output of 3.5w per channel. My idea is to use it with a dallas II horn, so with the fe206en (spl 96dbl).

I courrently own an unison research s2 that drives fonkens with the ff125wk. A good amp, but not exactly what I expected it to be..so I need to move on and build one on my own since I can't/ don't want to spend thousands of euros on an amp..

Thanks in advance for any help!

Ervin
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Old 30th August 2012, 12:12 AM   #2
Bigun is offline Bigun  Canada
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Hi Ervin,

Sounds like a nice plan - great and simple amp, nice speaker with good sensitivity. I think this is an excellent direction.

You weren't happy with your existing set-up - do you know it isn't the fault of the speaker ? In trying to change both the speaker and amplifier together you are not allowing for the possibility that only one of them is failing to meet your needs. The FF125WK is not a speaker I've heard, but I have heard other Fostex small cone drivers and I don't find them to be satisfying for all types of music, in fact due to some awkward peaks in the treble response I've found them a bit limiting. Not all fostex drivers are like that but the frequency response of the FF125 makes me nervous.

Perhaps you should go ahead and build that larger speaker you are interested in first. Let it break-in and try it with your existing amplifier. I believe it will give you another valuable piece of information to refine your plans.

I'm unfamiliar with the 45, but I read that the emission labs version is very pricy, it's perhaps not viewed by some as a true 45 but a new type with much higher output power. If you use this tube you may be very happy with it, but you would also be locking yourself in to a very specific tube with a single source of supply. If this is the amplifier to last a lifetime that is a risk.

I am planning to build a nice SET too, and I'm thinking that I should base it around the 2A3. There are many old NOS tubes to spend money on if you like, there are also many newer tubes on offer from different manufacturers. it will also give you those 3.5W you are looking for.

As for a schematic - there are so many to choose from and many of them are simple. I'm currently considering a simple design based on what I believe is used in Don Garbers Fi 2A3 amplifier. it's a direct coupled design, a single high-mu triode directly drives the 2A3. others on this forum with more experience than I can probably suggest other options with different advantages.
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Old 30th August 2012, 12:21 AM   #3
Bigun is offline Bigun  Canada
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here are some versions of the schematic that I referred to above - and I don't see why they wouldn't be equally useful for a 45 type tube with allowance for proper operating points

there are a few on the web, although I can't vouch for them Tubelab has a very good reputation:

http://www.tubelab.com/Simple45.htm

http://www.triodeel.com/simple45.gif

http://www.wavelengthaudio.com/bugle.pdf
Attached Images
File Type: jpg goodsoundclub_Direct_Coupled_SET.jpg (72.7 KB, 1273 views)
File Type: gif NobuShishido 2A3.gif (35.2 KB, 1245 views)
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Last edited by Bigun; 30th August 2012 at 12:25 AM.
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Old 30th August 2012, 01:16 AM   #4
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The Simple45 that Bigun linked to is the precursor to the TubelabSE, which makes a nice 45 based amp with mosfet followers. Tubelab sells the PCB's and if you pick up a power transformer with several secondary taps, you can build/modify the design to run 45's, 2A3's, or 300B's.

The 5842/417a front end is sufficient to drive any of the above power tubes using the followers.

Of course you could build it P-2-P as well......
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Old 30th August 2012, 10:34 AM   #5
castorG is offline castorG  Italy
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Hi Bigun,
Thank you for the help. It's not that I don't like the unison research, it sounds really good, but I don't think it is an amp worth all the money you need to buy it. I've always been in love with the unison research since I've been interested in hi-fi, so buying one it was like touching heaven for me!..but after listening to a small amp with some cheap el82 made by a guy (total cost around 200 euros), my reaction was to take my unison research and throw it out of the window! Of course my amp sounds better, but only a 10% I would say! But remember that we are talking about an amp that costs 9 times less than the unison.. (and it's not a question of tubes, since I have 2 old telefunken and also 2 svetlana C, some of the best el34..).

'So, if an amp made with ultra cheap componenets can sound almost like an 1800 euro amp, why don't build an amp with good parts on my own?', this is what I thought, and here I am, asking for some help.

Referring to the emission labs tubes maybe you are right, it would be a better idea to use 'normal' 45 tubes.

Ervin
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Old 30th August 2012, 10:55 AM   #6
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Default Hard to do better than this

Direct coupled, choke loaded, parallel feed, 45 with a constant current source on the driver. Meets your criteria for simple, and quality definitely depends on the choice of components. Note that direct coupling means you will be working with stacked (high) voltage. Not a good build for the easily distracted. What amp is?

Even though the design is going on 15 years old, all the parts are still available. CCS's may be had in kit form from several suppliers.

single
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Old 30th August 2012, 11:02 AM   #7
Bigun is offline Bigun  Canada
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A 'normal' 45 will have limited power output though. That's why I suggested the 2A3. Perhaps the 2A3 has become 'boring' because it became so popular, but I think it's a tube with a very strong pedigree and will give you that 3.5W you are looking for and which your speaker plans will benefit from.
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Old 30th August 2012, 11:50 AM   #8
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Hi!

This 46 am which I published on my blog is easily adaptable to 45 or 2A3:

VinylSavor: Single Ended Amplifier Concept, Part 7

Can even be made switchable between 45 and 2A3 with the right OPT

Thomas
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Old 30th August 2012, 01:18 PM   #9
castorG is offline castorG  Italy
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Thank you all guys!

After spending half a day on internet searching for a schematic and looking at your posts I've come to a conclusion..I want to build the amp buy jeff korneff.
From what people says it seems to be a really good amp.The only problem now is to find the schematic..does anyone have it?

Does anybody have any experience with this amp?

Ervin
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Old 30th August 2012, 04:18 PM   #10
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Had you not already come to a decision, I might suggest that you investigate transconductance amplifiers. They are ideally suited to single driver full range speakers.
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