My SE Scratch built mono amps

deafbykhorns

This was last years project for my horns.
Well, after taking a 10yr break from tubes I was inspired to build a 2A3 amp (really a 300b with the JJ 40W 2A3's) after hearing a good Eimac/2A3 combo. Looking back, I didn't realize the importance of using good iron and probably went back to transistors after building a JE labs style SRPP amp. That amp was a real disappointment and may of been due to using some crappy iron from a company up north somewhere. Can't remember the name but I heard he ripped off allot of people shortly after purchasing two trannies off his sleeze bay store. This time, I didn't hold back on this build. The first thing I did was contact Dave Slagle at the advice of a friend since the OPT was the backbone of this build. I then spent the next two weeks looking for tubes and found a guy locally that has about 100K tubes in his garage. I settled for the 26 and the 76 as final driver. With the help of a RCA Radiotron Handbook, SEcadd, autocadd, PSUD and a calculator I came up with a circuit. First time firing up, it was just about on the money. After testing on the scope with a sine/square wave, this amp came out really good, no ringing, good looking square wave and pretty darn flat below 20HZ. I believe it was a pretty good design but I think Slagles iron can make any amp sound better than most amps above $10K. Did I mention this amp is dead quiet, thanks to Rod Colemans gyrator supply on the #26. Jack Eliano helped me out with the chokes and power trannie using M6 iron, the chokes DCR measured much better than the Hammond stuff and has no hum or vibration. The ripple was minimal and looked just like the plot in PSUD when I checked with scope. Still tweaking the cathode and plate circuits but really close to having one of the best tube amps I have owned to date, period.

polkfarmboy

Very nice indeed sir, good work!!!

dromunds

Yeah, yeah!

mhardy6647

Works for me... hard to go wrong with 2A3 SE (even when they're 300Bs in disguise).

mhardy6647

Works for me... hard to go wrong with 2A3 SE (even when they're 300Bs in disguise). Messrs. Slagle & Eliano know their stuff, as well.

Dave does interesting things with coils of wire...


DSC_5259 by mhardy6647, on Flickr
DSC_5243 by mhardy6647, on Flickr

deafbykhorns

mhardy6647 wrote: »

Works for me... hard to go wrong with 2A3 SE (even when they're 300Bs in disguise). Messrs. Slagle & Eliano know their stuff, as well. Dave does interesting things with coils of wire...

You ain't kidding, Dave thinks outside the box and enjoys a challenge. I would love to hear those Jeffrey Jackson Eimac 75TL amps in which he designed the trannies to handle the extended bandwidth.

Dawgfish

Very nice!

organ

Very nice build! Do those JJ 2A3 actually sound like a 300B?
Going by your screen name, I'm assuming you're a Klipsch fan? I love their speakers. Have had the RF-35, RF-82 II, Cornwall, and La Scala. Getting a pair of RF-7 II soon.

deafbykhorns

Some say the JJ is actually a 300B with a 2.5v filament and a 40watt rating. It's actually better than some of the newer exotic 2A3's I've tried over the past year (one being Emission labs).
I've had a pair of Khorns since 1985 when I was doing pro sound installations. About 10-12 years ago, I was getting tired of the piercing horn sound and almost sold these until I stumbled across a filter engineers page by the name of Al Klappenberger.
His filter designs really changed the way these speakers behave which also prompted Klipsch to improve on their own filter networks. I actually delayed purchasing a pair of Polks because of this upgrade and still have all the Polk literature I have collected over the years. I'm not saying the Klipsch is better, its just different and performs well on a low powered tube amp.