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Old 6th October 2010, 03:53 AM   #1
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Default Need help starting

I'm trying to design a 25 W tube amplifier with push pull output for my senior project in electrical engineering. I'm using 6l6 for the output tubes and I know I want my output power to be 25 watts, but I don't know how to start designing the amp from there. Any help would be greatly appreciated
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Old 6th October 2010, 04:25 AM   #2
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Start with the tube manual, which will give you the voltages and currents needed to get the power you want. You will see which class of operation is most suitable.

Next step, design a power supply to provide those voltages. Then see what amplitude signal you need to drive it, and select a tube to do that (assuming you are building a complete amplifier).

You need to select a phase inversion scheme. Then you need to drive the phase inverter with a lower level stage. Finally, the feedback network.

I didn't mention the output transformer but that's part of the design of the push pull output stage.

Much of the project may be dictated by available parts, although nothing would stop you from winding your own transformers.
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Old 6th October 2010, 04:49 AM   #3
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if you are an ee (in training) this is at least at your level.
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Old 6th October 2010, 01:23 PM   #4
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I'd suggest you pick up a used copy of the Radiotron Designer's Handbook, THIRD edition (1941 or so). It might cost about $10 with postage. There's a later '50s edition, 1500 pages plus - you DON'T want to start there! Everything you need should be found with a little study.
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Old 6th October 2010, 03:03 PM   #5
SY is offline SY  United States
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RDH is a standard manual and everyone should have a copy of the 4th edition as an encyclopedic reference. For learning "how to design it," there's Morgan Jones's "Valve Amplifiers," and there's everything else. The 3rd edition is invaluable, very practical and (I think) perfect for what you want to do.
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Old 6th October 2010, 07:34 PM   #6
TheGimp is offline TheGimp  United States
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There is also the RDH4 PDF on the web, just search a little.

RDH3 and prior are no where the same as RDH4. I got 3 by mistake before I got the 4th. 3 is very basic compared to 4.
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Old 6th October 2010, 07:42 PM   #7
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Default Work Backwards....

Start with the operating conditions of the output tubes, determine B+ voltage and required input swing, then do the input stage/splitter, and finally, the power supply.

Check out Duncan Amps TDSL pages for the 6L6. There is a handy table for typical SE and PP operating conditions.

TDSL Tube search

Your operating choices are Triode, Ultralinear (with appropriate output transformers), and pentode.

While you're there, you may also want to download and use PSUDII (power supply designer II) free software for the design of the PS.

PSUD2

Turner audio also has a great section on designing amps, among the zillions of resources out there.

education+diy

Also, once you get the soldering iron warmed up, there is always this forum.................................

Last edited by boywonder; 6th October 2010 at 07:45 PM.
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Old 6th October 2010, 08:01 PM   #8
SHiFTY is offline SHiFTY  New Zealand
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If you already have a grasp for how vacuum tubes work (for example in a simple single ended amplifier), you could start reading up about the classic PP amplifier topologies, e.g. the Mullard 5-20 and the Williamson, their advantages and shortcomings.

Then you could start improving these designs- a lot of people now use mosfets, silicon rectification, high voltage regluators, constant-current sources and so forth to optimize the performance of the classic circuits and even provide protection for the expensive NOS valves. You might like to take a look at tubelab.com for an example.
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Old 6th October 2010, 08:12 PM   #9
taj is offline taj
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There is an excellent cut-to-the-chase, step-by-step guide called Designing Vacuum Tube Amplifiers, by Randy Couch. The best one I've read yet (with due respect to Morgan Jones.) It's a free e-book found here:

https://acrobat.com/#d=UjgTcfpvfqvboIiQLKn5rQ

The book is targeted at designing tube amplifiers for Jazz guitar, which are as clean as hi-fi amps (purposely low distortion), but usually bandwidth limited (no effort spent getting the response much beyond 50Hz - 6kHz). Clean and dark sounding. But the book certainly discusses methods of extending that bandwidth. It's is my favourite book so far.

Morgan Jones's Valve Amplifiers goes into much more detail and analysis, covering more situations, thus is slower reading if you're in a hurry, but still a must-have.

Pete Millet's website (Technical books online) has a gazillion antique books available to download. Norman Crowhurst is my favourite author among those.

..Todd

Last edited by taj; 6th October 2010 at 08:14 PM.
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Old 10th October 2010, 08:07 PM   #10
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How do I know how much gain to get from the driver stage?
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