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Old 24th May 2010, 06:59 PM   #1
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Default Minimalist PL519 OTL?

I'm thinking of trying my hand a a guitar amplifier, and was wondering if a set of PL519s configured push-pull in an OTL arrangement might be suitable. This is not quite as mad as it sounds - because many guitar speakers are 32 ohms or more, it shouldn't be too difficult to get a decent amount of power out of these tubes, and the lack of an output transformer makes it an extremely affordable project.

Can anyone recommend a fairly simple OTL design using these tubes? It need not have the highest performance - this is for guitar use, after all.
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Old 24th May 2010, 07:04 PM   #2
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OTLs work great for guitar.
Check these out:

YouTube - Tube OTL by Devildogamps

That's 6AS7 OTL with 6922s in the preamp.

Go for it!
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Old 24th May 2010, 07:12 PM   #3
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Btw, an OTL is not minimalist, and no cheaper than a simple vintage type guitar amp.
The O.T. for guitar are not the item that makes or breaks a budget for a guitar amp. The cheapest Edcors are great for guitar.
But I agree that with the right tube, and high impedance speakers, the OTL is a very good option.
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Old 24th May 2010, 07:21 PM   #4
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Originally Posted by SemperFi View Post
Btw, an OTL is not minimalist, and no cheaper than a simple vintage type guitar amp.
The O.T. for guitar are not the item that makes or breaks a budget for a guitar amp. The cheapest Edcors are great for guitar.
But I agree that with the right tube, and high impedance speakers, the OTL is a very good option.
I'm not so sure about that. The less desirable 519s are about $30-$40/pair on eBay, about the same as a pair of 6L6s. However, unlike the 6L6s, I don't need a $40 OPT...and, if I did my math correctly, I can get more power out of a pair of 519s into a 32-ohm load.
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Old 24th May 2010, 08:14 PM   #5
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Quote:
Originally Posted by Spasticteapot View Post
I'm thinking of trying my hand a a guitar amplifier, and was wondering if a set of PL519s configured push-pull in an OTL arrangement might be suitable. This is not quite as mad as it sounds - because many guitar speakers are 32 ohms or more, it shouldn't be too difficult to get a decent amount of power out of these tubes, and the lack of an output transformer makes it an extremely affordable project.

Can anyone recommend a fairly simple OTL design using these tubes? It need not have the highest performance - this is for guitar use, after all.
You might want to look here for a simple, reliable circuit:

http://www.diyaudio.com/forums/tubes...-new-post.html

I built a guitar amplifier based on nearly the same circuit, which looks like this. It runs 16 ohms with about 20 watts and about 50 into 32 ohms. Very nice tone and does bass really well. Instead of PL519s, it uses 6AS7Gs (which are cheaper and easier to find) but you could use PL519s in triode and it would work, though not with as much power. You would need a few more PL519s (six, I think) before they would make more power than the equivalent number of 6AS7Gs.
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Old 24th May 2010, 08:21 PM   #6
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Originally Posted by atmasphere View Post
You might want to look here for a simple, reliable circuit:

http://www.diyaudio.com/forums/tubes...-new-post.html
I like the idea of your circuit, but that doesn't seem to point to anything OTL-related.
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Old 24th May 2010, 08:42 PM   #7
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Quote:
Originally Posted by Spasticteapot View Post
I like the idea of your circuit, but that doesn't seem to point to anything OTL-related.
Oops! sorry about that- had the wrong text in my buffer. Here's the correct link. Most of the rest of the thread relates to that circuit.

What tubes for a tube amp?

Last edited by atmasphere; 24th May 2010 at 08:45 PM.
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Old 25th May 2010, 03:37 AM   #8
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Originally Posted by atmasphere View Post
Oops! sorry about that- had the wrong text in my buffer. Here's the correct link. Most of the rest of the thread relates to that circuit.

What tubes for a tube amp?
Any specifics on yours? I figure I may as well duplicate a known-good design.

Also, yours uses a single 6SN7 with two smaller tubes, which is very much different from the standard Atma-Sphere design.
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Old 25th May 2010, 04:08 AM   #9
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The 6SN7 is the driver tube, direct-coupled to the power tubes as you see in the schematic below, from the other thread. The smaller tubes are 12AT7s, arranged in a differential cascode as seen below, only without the CCS, and of course there are only 4 power tubes. I raised the power tube B+ to nearly 200V, and reduced the plate current to about 30 ma, to allow the amp to take advantage of a higher impedance load. It makes about 50-55 watts into 32 ohms.

I'm working on an OTL with an input transformer, the idea being that the front end of the amp is entirely single-ended, to keep the circuit as simple as possible, and allow for extra gain, volume controls and a tone stack. Its an idea I've had for a while, thinking that the 'pure' OTL would be lacking in the overdrive department (which turned out to not be the case at all- it has a fabulous overdrive sound!!). I was thinking I could get a little 'magnetic saturation' quality into the overdrive, without paying the price and weight of an OPT. If it works I'll post a schematic.

In the meantime, the 'pure' OTL approach works really well, and is also quite reliable, even in overdrive.
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Old 25th May 2010, 04:16 AM   #10
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If you don't mind my asking, what, exactly, is a CCS?

Also, did you use the full-fat Atma-Sphere PSU, or perhaps something simpler?
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