Dynaco A-25 Speakers Restoration

WE91 clone Project

WE91 (Western Electric 91) 300B Clone Amp

JJ 300B (4oW heat dissipation) driven by 5693 pentodes

Conservatively around 9 wpc

Completed Feb 2008

So, I have been building loads of SET amps in pursuit of sonic perfection (more like psychological warfare) and I have come to a conclusion that such a thing is unattainable until I built this. I guess what really happen was I built something that I can be content with for a long time to come. I have built several DHT single ended triode amps with big bottles such as 300Bs, 6B4Gs, 2A3s, etc. in various combinations of designs, and I kept finding myelf comparing them not upto par with some of the Darling amps that I built. What was really disappointing was that Darling amps cost only 1/3 of these amps to build!

I did have high hopes in the WE91A. I have been studying this amp for a while on the web, and, after talking with Raymond Koonce who built many of WE91A clones, I decided to embark on building one for myself. It wasn’t an easy decision because parts cost alone was going to be well over a grand. I also wanted to custom paint the chassis, so it was going to be double the work.

I really didn't want to compromise on parts used for this amp. I wanted make sure that this amps will last for a long time to come. Every part used well exceeded in their respective power handling ratings. A good example of this is the Hammond's OPTs that are rated 30W. The amps only puts out 9 wpc. There are in all 9 irons, three of which weigh 35 lbs together. My estimate of the finished amp is around 55 lbs.


I detest tube amps with PCBs, mostly because I like to do things in old school fashion. Everything is point-to-point wired. I tried using as few electrolytics as possible. The only places that I used electrolytics were bypass and filament bias caps. The bypass caps are Black Gates. I used Solens in many places. The coupling caps are Hovlands. The filter caps (large silvers one sticking out on top) are oil filled ASC polypropylene caps. I could have saved a lot of money using alternate parts, but I didn't want to. The power supply section is very robust with a split rail PS with separate chokes.




I was originally going to have the chassis and iron bells powdercoated, but it didn't work out due high cost and lead time. So, I decided to just spray paint the whole thing using automotive paint and clearcoat. It was a lot of work. I put on at least 5 coats of cherry red paint + buffing with rubbing compound in between coats. I then put on about 8 layers of clearcoats with buffing in between coats. I then baked the whole thing at 145'F overnight. I guess it came out alright. I also have to mention that I learnt an important lesson. I neglected to wear a respirator while spraying and really compromised my immune system. I came down with the flu the next day, from which I was bedridden for 3 days. The flu lasted about a full week.

I have never punched or drilled this many holes before. I still marvel at how I fitted all that stuff in a 17x10x3 steel chassis.

Ok, so how did it sound? When I heard it play music for the first time, I said to myself, "Finally, this is what I'm talking about!" I think I have finally found a 300B amp that I could fall in love with. JE Labs 300B was alright, so was GSG 300B hybrid, but they weren't anything that I would get excited about.

The WE91A is so SMOOTH. This amp makes listening so effortless. Even with some of tube amps I have, which I think are decent sounding by anyone's standard, I would get hearing fatigue after a few hours. This one could sing the whole day for I care.
I don't know what it is - 5693 pentode drivers, the design, voodoo- whatever it is it's working for me and I am loving it. Was it worth the flu, money, and time? Absolutely! All that was forgotten when I heard it play my favorite records for the first time.