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Old 30th April 2013, 12:24 AM   #1
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Default 50W PP - KT88 Build

Good Day my Fellow Vintage Followers

After many hours of browsing, looking and Trolling I have decided to take the tumble and build my own amplifier. I am no Audiophile, nor a Valve expert. I am a new age Electronic Engineer..

My first introduction was from Gio Militano and his OddWatt Kit he build with KT88 and 5751 (Very nice Gio).

I ordered my KT88 Genalex Golden Lions and Electro Harmonics 5751. But after many hours of looking at the OddWatt design I must say the design concept just alludes me. Thus I searched more and found many different designs like the Noavolta, Williamson and many more. These amplifiers is bit more understandable and follow design topology I am more familiar with.

I have also found that you can have a single ended or a Push pull configuration. As I have a set of KEF Q5 series speakers and the Single ended design would not be able to deliver the power (unless you look at parallel), thus I have settled for a Push-Pull Configuration (50Watt)

I am about to start my Chassis design but currently contemplating my Transformers selection and can not make decide if I would go mono block (3 boxes) or stereo setup(1 box)... As we al know weight do increase if you choose one enclosure...

I also can not seem to decide on my Transformer manufacturer or topology
1) Edcor
2) Hammond
Or do I go with Toroidal Power and Normal Output Transformers.. Or keep all Toroidal or keep all Normal...

Thanks all..just want to say hi and get my project on the board.. Feedback would be nice.. Will post more pictures and Schematics as I progress...
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Old 30th April 2013, 02:28 AM   #2
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I prefer Edcor over Hammond, although I have not used their 300 series power transformers (they are a bit higher quality than the 200 series)

Edcor now also makes chokes, and you can order everything in black if you are not fond of the std blue fare (finally!!)

Another question to ponder is triode or UL wired KT88's.......

The Williamson topology can be a bit tricky to get stable and requires high quality output transformers. One of the experts here may be able to shed some additional light on this if you are interested.

The Mullard 5-20 topology is a very straightforward proven topology that can easily be made to work with KT88's.

Here are a couple of threads for PP KT88 projects:

"Mullard 5-20 KT88 PP blocks!

OPUS 5.0 A Modern Mullard

KT88 Monoblocks are a lot lighter than a stereo build and the halving the current requirements makes power transformer and choke selection easier. Of course you need to build two chassis and two power supplies.

Last edited by boywonder; 30th April 2013 at 02:51 AM.
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Old 30th April 2013, 04:02 AM   #3
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Quote:
Originally Posted by boywonder View Post
The Williamson topology can be a bit tricky to get stable and requires high quality output transformers. One of the experts here may be able to shed some additional light on this if you are interested.
I've always wondered about that statement. No doubt the original Williamson trannies were well wound. However, are they significantly better than what Edcor (or Hammond) will sell today, or just significantly better than what was typically available in the late 40s, and early 50s?
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Old 30th April 2013, 04:22 AM   #4
TiMBoZ is offline TiMBoZ  Australia
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I'm interested in same...

There is a pretty complete, well documented build/thread Loren 42's: My KT88 Williamson Amp Build using PCB's and Edcor Transformers. Also with XLR inputs.

I'm interested in building something similar to this, but point-to-point...
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Old 30th April 2013, 04:50 AM   #5
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I must say that I also liked the Build from Loren. The only thing that is missing is the power section and I am not sure what Power Trafo's he is using.. But that was the first AMP I saw after the Oddwatt and I want it..haha
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Old 30th April 2013, 11:15 AM   #6
Loren42 is offline Loren42  United States
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Originally Posted by Maveric Pta View Post
I must say that I also liked the Build from Loren. The only thing that is missing is the power section and I am not sure what Power Trafo's he is using.. But that was the first AMP I saw after the Oddwatt and I want it..haha
Here it is.

My KT88 Williamson Amp Build

50+ WPC, it is two separate amps on a single chassis weighing in at 45 pounds. Chassis size is 17" x 10" x 2" with extra 1/4" aluminum plates for structural integrity.

The power transformers are two Edcor XPWR133

The output transformers are Edcor CXPP100-MS-4.2

Topology is Williamson.

Click the image to open in full size.
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Old 30th April 2013, 11:25 AM   #7
Loren42 is offline Loren42  United States
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Here is the power supply schematic. Some of the resistor values may have been tweaked, but the listed output voltages are what you want.

Click the image to open in full size.
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Old 30th April 2013, 01:32 PM   #8
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If building a Williamson, including Loren's version, you might want to search for the 'Improving the Williamson Amplifier' by Talbot Wright, and another article which confirms Wright's findings 'Williamson Tube Amplifier Modifications' by Chimera Laboratories. The only changes both articles suggest is some resistor values to improve the performance of the preamp (1st stage) the splitter (2nd stage) and the driver (3rd stage). I would think those findings would hold true regardless of whether using cathode bias (as per the original Williamson) or fixed (as per Loren's)
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Old 30th April 2013, 01:38 PM   #9
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by prairieboy View Post
If building a Williamson, including Loren's version, you might want to search for the 'Improving the Williamson Amplifier' by Talbot Wright, and another article which confirms Wright's findings 'Williamson Tube Amplifier Modifications' by Chimera Laboratories. The only changes both articles suggest is some resistor values to improve the performance of the preamp (1st stage) the splitter (2nd stage) and the driver (3rd stage). I would think those findings would hold true regardless of whether using cathode bias (as per the original Williamson) or fixed (as per Loren's)
+1
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Old 30th April 2013, 05:14 PM   #10
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Quote:
Originally Posted by prairieboy View Post
If building a Williamson, including Loren's version, you might want to search for the 'Improving the Williamson Amplifier' by Talbot Wright,
Exactly !
Also, I would like to add one more article - "Modernize your Williamson Amplifier" by David Hafler. Combine these 2, plus UL + CFB, and you will get ultimate Williamson.

Breadboard with Williamson shown on picture (the top one).
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