thanks guys, for a lot of people, that was their first time to hear and experience an OTL tube amp.......
a wrote a short whitepaper, giving the lowdown on the 6C33C OTL tube amp,,,,,,
6C33 OTL amp….a white paper
The single biggest factor that controls the sound of any tube power amp is its output transformer or OPT. Getting the correct OPT is the deal maker in any tube power amp, get it right and you get a very good sounding amplifier. While some will argue tubes, but tubes are easy, once you get your tube amp, it is very easy to replace tubes to get the flavor that you like; this is called tube rolling… To quote Tim de Paravicini, “it is all about the topology and the output transformer….” He after all was the designer of that legendary Luxman MB3045…
Let us look at the OPT for while, easily the single most expensive part of any tube power amplifier. You need the irons in the OPT to transfer energy i.e. from the output tubes to the speakers, since the impedances Involved are not the same, tubes being of high impedance and speakers of low impedances, OPT’s therefore are mandatory…There are a lot of physics involved in the design, and they are more often than not contradictory, and so design compromises have to made. To avoid low frequency saturation, the irons or the core have to be massive, but making the core massive increases leakage inductance and so high frequencies are severely attenuated. In other words the OPT is also the chink in the tube power amplifier’s armor….Designing and making them involved a lot of compromises, so that some call it more of an art than science….
What if the OPT is done away with altogether? Then we will not have to suffer the pitfalls of having an OPT in our tube power amps. Julius Futterman did just that publishing and article in 1954 and then in 1956...He also started building them by hand using the 6AS7 or 6080 tubes...Today, tubes like the Russian 6C33C are used and one design by Tim Mellows being built by audio builders all around the world. I made myself one such amp….the Russian 6C33C is very similar to the American 6336 tube...Other tubes that are used are the TV tube the PL504/6KG6, but other TV tubes like the 6LW6, and the 6LF6, etc. are equally as good to use in OTL amplifiers.
So I made a 6C33C power amp capable of 25 watts into an 8 ohm speaker and about 40 watts into 4 ohm speakers. Since there are no OPT’s the amplifier is now lighter, and frequency response is now better, all frequencies get amplified equally…this amplifier draws 350 watts at idle and about 400 watts at full power… Tony Tecson
