Hi Everyone, There seems to be a bit of interest in the various versions of the Oddwatt amp EL84 project
I posted a few months ago. So I thought this forum would be a good place to talk about other versions completed or in the works. First I don't claim to have originated the basic circuit of the output stage. I can track its origins back about 55 years and then it seems to be lost. The idea to use a CCS in the cathodes was posted in a project on the diyparidise site a while ago. SRPP stages have also been around a long time as well. I suppose if I can take credit for anything it is the combination of the two circuits. It would appear that neither by itself is all that wonderful. The pair though work very well together, far better than I would expect. Both parts have things in their favor. The SRPP is highly immune to power supply noise and can drive difficult loads easily. The output stage is simple in the extreme and also is rather immune to power supply hum and noise. Together they make a quiet amp. It can only operate in class A mode, but is very adaptable to other tubes, and modes (triode, UL, pentode). So much for the background and disclaimers.
The amp I use most now is the KT77 (OD225) version
. It has a robust and refined sound. I won't go into all sorts of other terms as we probably couldn't agree on what they mean anyhow. I personally think it sounds better than anything else I own (3 vintage SS amps by Marantz, a Kenwood, Pioneer, Super Ts, a LM3875 gainclone
, a modified K-12 tube amplifier kit
, and a number of lessor ones). The OD225 works well with 6L6GCs too. It has an even more robust sound with a little more distortion (about 0.3%) and a little less refined sound. Great for rock music.
My present project is a variation that uses KT88s. It is about 50% completed. I'll see if I can post images of the progress.
For those of you who may find tube amp building a parts collection nightmare, myself and another diyer (Hi Rodney) are working on putting together parts kits complete with PCBs for the KT77 and KT88 versions. Since only quality parts are being included it won't be cheap, but then no reasonable tube amp in this size range is. Stay tuned on the kit issue, we are still a few months away from that.