• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

What do you think??????

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lawbadman

lawbadman

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Joined 2003
#1
Hello all,
Now that finals are over I am looking for a tube amp project. I need something with at least 20 watts (mainly because I cant afford anything with much more power). This poses a challenge as my speakers are magnepan MMGs, they are a bit inefficient and they are 4 ohms. I have an output trafo which is 20w with a 6K6 primary, it would be great to find an amp which I could use it in maybe a 6L6.

I was searching and found the OLT amp which I attached below. It came from the Evolve Amplifiers web site. It looks nice and simple, it might be a bit costly bit I think I might just take the risk.
The big question is will it be able to handle my MMGs?
I am not looking for high SPL just good sound at moderate volumes.

Any comments on the combination?
Other suggestions are most welcome.




Thanks
Lawrence
 

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#3
That circuit is quite complex and unconventional for a tube amp, however as long as you can build a power supply for it you should be ok. I think you would need a pretty beefy (expensive) power transformer for that one.

However it is certainly not the only way to go- if you can score a couple of matching output transformers, and a power transformer, a simple EL84 PP or EL34 PP will give you enough power. Even 10W should be enough to get reasonable volume levels. Schematics abound on the net.

For simplicity's sake, I would recommend considering a kit, you get a nice chassis and a tested design to start with. Then, you can mod to your hearts content... 🙂

Either that, or rebuild a vintage amp...
 
#5
Ouch! He's right, OTL is the worst way to go, unless you want something huge, inefficient, and expensive. And one which will be frightfully difficult to make reliable.

You've got 6.6K transformers. Those are perfect for 6L6 or EL34. That will still be pretty marginal power for MMGs- you really need at least 100W to make them sing, unless all the music you listen to has compressed dynamic range.
 
#6
I've driven Maggies (MG-I's I think) to pretty decent levels with a PP 6V6 amp at a "casual" party..you still had to raise your voice over the music.
People have always said "Ohh Maggies are power hungry,you need atleast 100W,solid state,etc." Bah,Just give it a try..

Afformentioned amp-
http://www.users.qwest.net/~ptaylor/Audio/6V6PPamp/6V6amppage.html

Maggies are a low impedance load,but are nearly purely resistive..despite the low impedance,that's still a fairly easy load for an amp. (compared to a 4-ohm voice coil.)
 
#7
Hello all,
I agree with DigitalJunkie. A small tube amp can make maggies sing but just not at very high levels. I plan to make a UCD400/700 amp for the maggies anyway, I just want to jump into the tube world. The main reason for going with tubes is that there has been a lot of noise on AA about how good maggies sound with tube amps, even small ones (sacrificing high SPL of course).

So with that I, have attached the amp that I am going to build. It seems a bit old, does anyone have any ideas of how to improve the circuit or is it fine as it is?
I also plan to use KT66 instead of the 6L6 (if my wallet allows).



Thanks
Lawrence
 

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#9
Re: 300B PSE 18W

DigitalJunkie said:
I've driven Maggies (MG-I's I think) to pretty decent levels with a PP 6V6 amp at a "casual" party..you still had to raise your voice over the music.
People have always said "Ohh Maggies are power hungry,you need atleast 100W,solid state,etc." Bah,Just give it a try..
Click to expand...

My $0.02

so have I (PP 6v6 driving a MG-Ii) and the volume was okay, but 10W just didn't do the bass justice.

don't get me wrong, I prefer tubes, but around 10W of 6v6 power just won't float your boat with a MMG - why, even a 50Watt NAD SS integrated didn't when I had a pair of MMG on loan. Those speakers can be stubborn to drive.

I would look at using something like a 6L6 or EL34 push pull (or push pull parallel), .. perhaps tubesomething in the 20W range or more, or perhaps a circuit based on dynaco 70 , fisher 500 or so ,

pay attention to your power supply if you build from scratch
good luck
 
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