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Old 4th December 2002, 01:25 PM   #1
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Default First time Tube Amp

Can someone point me in the direction of a schematic to build a tube amp. I am a first time tube DIYer and am having trouble finding a good first project.

Im looking for a somewhat proven design that provides good results and would be a good first project.

Also, the kits that you can buy; Is it significantly cheaper to build from a schematicas oppossed to the kit price?

Thanks,
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Old 4th December 2002, 03:52 PM   #2
Joel is offline Joel  United States
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Default Re: First time Tube Amp

Quote:
Originally posted by Milzie
Can someone point me in the direction of a schematic to build a tube amp. I am a first time tube DIYer and am having trouble finding a good first project.
Im looking for a somewhat proven design that provides good results and would be a good first project.
This is really vague. What do you mean by good results? What type of speakers do you want to drive? What source are you going to use? How big is your listening room? And what is your budget?
All of these things will dictate the answer.

Also, the kits that you can buy; Is it significantly cheaper to build from a schematicas oppossed to the kit price?

In most cases, no. But it's more fun to shop on your own, and you can also select every component to meet your needs.

Joel
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Old 4th December 2002, 05:12 PM   #3
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I guess by good results, Im looking for a design that has already been completed with no hum, noise, etc problems. Something that is generally regarded as a good design.

I would like to keep my budget to less than $500

Source will be CD

Listening room is small, about 12 by 12

Speakers are DIY using Morel MW-164 and MDT-30



By the sounds of it, a kit may be my best bet?????
Any recommendations for a good kit that is point to point, no PCB's, as I feel its a better way to learn as oppossed to just soldering a bunch of components to a board.
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Old 4th December 2002, 05:30 PM   #4
Joel is offline Joel  United States
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Well, hum and noise are more a problem with layout - usually - and that comes with knowing the basics. Looking at commercial amp layouts will help a lot.

I'm not familiar with those speakers. What is the sensitivity rating? If it's high, you could start with a simple single-ended amp. One 6SL7 gain stage, and a triode-wired EL84. That was my first DIY amp, and it was reliable, and good sounding. Cost was under $250.
Is that the last word in amps? Hell no. But the point of the first amp is to allow you to make mistakes, and learn. It helps if the end result is something you want to listen to as well! Take a look at the Decware "Zen". That's the basic topology I'm referring to, but you can make one for a lot less than they charge. Output, 2 watts.

Obviously, if your speakers are low sensitivity, you should probably start with something more powerfull.
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Old 4th December 2002, 06:00 PM   #5
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The woofers are rated at 86dB

By the sounds of your fist prject, its exactly what I am looking for. I want to learn. I dont want to invest a lot of money in case of screw ups, and I want to end up with something that I would be happy to listen to.

Would 2 watts be enough for my speakers? DO you have the schematic that you could send me?
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Old 4th December 2002, 06:09 PM   #6
Joel is offline Joel  United States
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Milzie,
It might not be the best match for your speakers (god those are inefficient!!!)... but it is a great project to learn on. With only a single gain stage, there is no chance of oscillation, or coupling problems, and there is a minimal parts count. It's the simplest form of amplifier you can make. (I think that's why it sounds good too).

I'd be happy to post a schematic and parts list as soon as I can.
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Old 4th December 2002, 06:25 PM   #7
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Thats fine if it doesnt match my speakers very well. Just gives me an excuse to build another set!

They may be inefficient, but they sound incredible!

I would very much appreciate it if you could post the schematic and parts list, or send it to me via email.

jeff.mills@sympatico.ca
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Old 4th December 2002, 07:57 PM   #8
Joel is offline Joel  United States
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Default schematic

milzie,
Ok, here it is. I make no claims that this is original, or daring in any way (except maybe the 5755) - but it works good, is pleasant to listen to, and is about as easy as you can get.

After you build something like this, you can move on to more complex topologies, or directly-heated tubes, etc.

Parts list to follow.
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Old 4th December 2002, 08:06 PM   #9
Joel is offline Joel  United States
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Default Parts list

Raytheon 5755 twin triode (1)
EL84 pentodes (2)
5Y3GT rectifier (1)
Power transformer, Hammond 272DX, 300volts/ct@125mA (1)
Output transformers, Hammond 125ESE (2)
RCA input jacks (2)
Speaker binding posts (4)
On/Off SPDT switch (1)
Fuse holder (1)
3-prong power cord, 6 ft (1)
Chassis, Hammond aluminum, 8x12x2
Rubber feet (4)
.1uF-400 volt capacitor (2)
100uF-35 volt capacitor (2)
100uF-450 volt capacitor (1)
40uF-450 volt capacitor (1)
500-ohm 5w resistor (2)
100-ohm 5w resistor (4)
100-ohm 1w resistor (2)
10k-ohm 1/2w resistor (2)
1.8k-ohm 1/2w resistor (2)
100k-ohm 1/2w resistor (2)
220k-ohm 1/2w resistor (2)
270-ohm 5w resistor (2)
Volume potentiometer, dual-ganged, 100k-ohm, audio taper.
9-pin tube socket (3)
Copper hookup wire, 18-22gauge

You can get most of these at angela.com or someplace similar online, and the remainder at radioshack. I wouldn't buy any expensive parts for your first project - carbon film resistors, polyester and electrolytic capacitors, and import tubes will work just fine for you. I recommend Ei brand EL84's - they are cheap and they work. The 5755's are $2 at angela instruments. They also sell cheap 5Y3GT's.
If you want better fidelity (maybe), upgrade the output trannies to the $89 Hammond 1628SE they sell. Only drawback is they are 11lbs each!

Good luck.

Joel
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Old 5th December 2002, 09:10 AM   #10
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Default Re: Parts list

Quote:
Originally posted by Joel
If you want better fidelity (maybe), upgrade the output trannies to the $89 Hammond 1628SE they sell. Only drawback is they are 11lbs each!
If you want to get these ones, get them from Electro Sonic. Cheapest place i could find them -- and they are in Ontario (and from your email address i'm guessing you are too. One of the reasons is that they are much closer to the factory.

http://www.e-sonic.com

I was quoted $122.25 CAD each in March.

The EL84 is a nice amp. If you run it in pentode you can get double the power -- 4 W -- out of it. A little more complex, and perhaps not as good sounding (i never got around to wiring mine in triode i was enjoying it so much -- now on the bench for a refurb).

A real cheap way to get the basic elements of an SE EL84 amp is to scope up an old console, gut the amp and rebuild it. You could probably do the thing for less than $100 CAD going this route.

dave
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