Roger's Tube Amplifiers & Transformers Homepage

Welcome to Roger's Homepage!
Created by Roger Knopp, M.Sc.E.E
phone/fax: +46 31 252345

Musiclover as I am, I've been building several tube amps since 1991. This includes two MM preamps, a guitar amplifier and three former versions of the power amplifier KEW88-91D, which is my fourth and final attempt in building a cheap while good stereo Valve Amplifier as inspired by D.T.N Williamson's design of 1947. Several problems has however come to my attention since I first started and most importantly that is the cost and availability of functional bandwidth sensitive high voltage transformers. In an effort in minimizing customer costs as well as my own I started around 1992 to develop transformers of my own and I'm now proud to announce that I have fully functional and quite cheap transformers as well as Williamson Power Amps for sale.

Roger's Tube Amplifiers

The Williamson Power Amplifier Kit KEW88-91D/CH1 is my final stereo
Williamson solution for handy audiophiles. The kit will include everything neccesary,
except tubes, for complete Williamson assembly. Other order possibilities are:

KEW88-91D/CH1: Roger's Williamson Amplifier Kit (without tubes): 750 USD
KEW88-91D/CH2: Fully Assembled Williamson Amp (without tubes): 1250 USD
KEW88-91D/CH3: Complete set of tubes (EH 6SN7GT + Sovtek KT88): 250 USD
KE57613C: Roger's Williamson Output Transformer: 10 pcs at 750 USD
KE77003B: Roger's Williamson Mains Transformer: 10 pcs at 1250 USD
KE87060: Roger's Universal Power Transformer: 10 pcs at 1600 USD
Payment terms: Cash with order. See for cheaper tubes.

Roger's Williamson Amplifier Kit (tubes excluded)

The output transformer KE57613-C is my third attempt in designing a cheap but fully functional OPT for my Williamson amplifiers. The OPT is a simple but good transformer featuring a frequency response of 4Hz-45kHz while using KT66 push-pull drive. Moreover it uses a special core material with high mmf tolerance thus eliminating the need for tight DC&AC tube matching and may even be used in some Class AB mode. The OPT is however recommended to be used in pure Class A configuration only which by default has some inherent Class AB "problems" such as bias unbalance, tetrodes and most importantly the loudspeaker impedance vs frequency. Generally it is not recommended to use loudspeakers with a nominal impedance variation of more than +/-25% (unless bias is Class A corrected). That is a minimum 6Ohm speaker load at the standard KT66 armed Williamson output.

Roger's Output Transformers

The universal transformer KE87060 is my first attempt in merging my Williamson OPT KE57613-C+ with my Williamson MT KE77003-B and thereby minimizing the cost and number of different components in a design. The UNI is a quite simple but, at current version, a bit expensive transformer featuring extremely universal usage possibilities. The transformer has for instance 4 separate balanced wide bandwidth primary windings which may be used either as 50% UL OPT or as high power mains isolation. Moreover it has a number of high current secondary windings which fulfills most audio tube heating needs as well as speaker matching in case of OPT usage. Two high voltage secondary windings are also integrated which can be used to supply a Williamson PA as well as many other types one perhaps would like to build.

Roger's Power Transformers

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Phone: +46 31 252345
Fax: +46 31 252345
Address: Danska v.85:2, SE-41659 Gothenburg, Sweden