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    Building, troubleshooting and testing of these amplifiers should only be
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50W PP - KT88 Build

Maveric Pta

Member
2013-04-29 12:10 am
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)...:confused: 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...:confused:

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...
 
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:

http://www.diyaudio.com/forums/tubes-valves/156699-mullard-5-20-kt88-pp-blocks.html

http://www.diyaudio.com/forums/tubes-valves/161702-opus-5-0-modern-mullard.html

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.
 
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prairieboy

Member
Paid Member
2010-11-22 2:31 am
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?
 
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. :)

http://www.diyaudio.com/forums/tubes-valves/158322-my-kt88-williamson-amp-build.html

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.

[IMGHTTPDEAD]http://www.mdbq.net/trex/t-rex1.jpg[/IMGHTTPDEAD]
 

prairieboy

Member
Paid Member
2010-11-22 2:31 am
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)
 
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
 
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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Maveric Pta

Member
2013-04-29 12:10 am
Good Day All...thanks for your posts.. I appreciate it

I will be basing my design on Loren's design and take in consideration the Williamson updates stated earlier above.

Thus my preamplifier section will consist of 12AX7 and 12AU7 if I can not get my hands on the 6SN7GT. I would liek to use the 5751 as they have a biot more gain in them than the 12AU / 12AX and the 6SN.

I would liek to use a PCB design rather than point-to-point wiring.

Loren42: Do you still have some PCB's left?

The Transformers will be coming from Edcor

Output Transformer CXPP60-MS-4.2K - As this amplifier would be 50Watts rated and I think you can not get more that 50watts out of the KT88 unless you drive them parallel, thus I feel that the 100W version would never be used to its potencial and I would rather save the $40.

Power transformer can not be the XPW133 stated as our primary voltage here in Australia is 'n bit higher than 110VAC. thus I am waiting for Edcor to respond if they can supply a 240VAC version of the XPWR133.

Color on the Edcor would be black if I can choose...

Enclosure will be custom and would be a stereo setup rather than a Mono block setup.

Once Edcor has confirmed availability and my order to them I will start with my enclosure design and component placement .. If I can get some PCB's nice...otherwise I will do point-to-point.. (Might think making my own PCB's... if my financial officer don't mind an extra $500 expense for the PCB's..:))
 
Get the 100W OPT as the bandwidth will be much better at full power & with less distortion. Many 6550/KT-88 amps got 60W/CH (Dynaco & Harman Kardon) and at least one with 70W (Heatkit) was made. The bigger OPT's will support KT-120 tubes better also if you want to try them latter also!

Anyway when your doing it you may as well do it right for only a very small % of the total cost more. The OPT's are what define the ultimate sonics of your tube amp also, so if you can afford the extra on PCB's look for better OPT's.

Don't rush, do your due dilligence!

http://www.diyaudio.com/forums/tubes-valves/234964-best-pp-opt-30-100w-range-2.html
 
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multi

R.I.P.
2011-01-28 2:52 am
KT88 50 watt

Best to stick with Lorens design maybe changing some of the resistor values.
12AX7's 5751's are best left to Guitar amps and pre-amps, you don't need extra gain with the Williamson. Other driver tubes are 12BH7, Russian 6N6 or ECC99.
the design by Triode Dick is also very good.
The 6550/KT88 can easily give 100 watts, but last longer at 70 watts or less.
Phil
R18 is better reduced to 470r not 1k may be printing mistake on the input voltage amp used on Triode Dicks Monobills classic, circuit
 

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multi

R.I.P.
2011-01-28 2:52 am
One advantage of Triode dicks circuit is the grid resistor on the KT88' of 39k.
Current production 6550's, KT120's recommend less than 50K, Fixed bias. Original GEC KT88's could handle 100K, but even so many of GEC's circuits used 39k and 68K, to extend tube life. Not sure but 6SN7's may have trouble working into 39K, the 6N6 has very low plate resistance so easily drives 39K..
Phil
 
Williamson circuit has enough gain as it is, doesn't it? Why add 12AX7? Also, there are Russian 6SN7GT available. That's what it is in the pretty picture from earlier in this thread. In addition, 12AU7 does not perform as well as 6SN7.

I am now running some NOS PhillipsECG JAN 6SN7WGTA tubes instead of the Russian tubes and the KT88s have been replaced with reissue Gold Lions.
 
Good day my fellow Valve heads :)p)

Thanks for the advise..

Ok..I will be sticking to Lorens design as I have all the info I need. It is a sweet amp and it looks the parts as well.

I had a look at the Jadis amplifier and even found a Defy 7 schematic..But looking at that I would have to start from scratch again.. What Power Transformers do they use? what OPT do they use..

Loren was kind enough to share his design and all the info required to build the amplifier. For first time builders and Novices like myself this is to me the best option.

I have placed my order with EDCOR.. The OPT is the CXPP100-MS-4.2K as advised by people with better knowledge (and I can understand the madness behind the argument for a bigger OPT). The Power Transformer is the XPWR133.. but with a $40 charge they are making the XPWR133-240 for me.

So next step will be to layout my Enclosure and get it laser cut and folder .. I was looking at a few posts where stereo enclosure seem to have a weakness due to the weight and the available enclosures in the market.. Thus I am opting for a 2mm stainless enclosure designed.

I am currently looking into a few volume controls ..either ALPS or a
23 Step Attenuator.. Inputs would be selectable between 3 sources..

Seems I will be doing a point to point wiring at this stage as budget was taken up with the transformers. But this might be a good point as this would provide me with easy changes if any resistors needs changing and then it would also allow me to upgrade and do design changes if I require to update with KT120 as mentioned prior in this threat..

Will keep you guys posted and on my progress...
 
Good Day my fellow Valve lovers

Finaly got my Transformers from Edcor. I must say..Wow..they look great..hope they sound as good as they look.

Loren42... Wow man..the output transformers are actually bigger than the power transformers.

Now for my enclosure... I had a good and hard thought and I have decided I will be doing a single enclosure.. Might be heavy and big but I would rather have one than three enclosures to build.

Enclosure design is still up in the air..still looking for acceptable enclosure from supplier or maybe design my own..

Will keep you posted and start loading photos

Happy building