Western Electric 91A WE91A
Clone 300B Amplifiers
2x 300Bs, 2x 6J7s, and 2x 5Z3s
Built based on Joe Roberts' Schematic
Completed on 8/18/08
"Hi, I just wanted to compliment you on your craftsmanship, I purchased the 300b monos last year that you had
built for a customer. He listed them on audiogon for a price that was just insane, I paid $750 for them with the tubes which
are the mesh plate 300b's. I am using a set of Decware fullrange speakers with the flex cabinets that are customed just for
this driver. I have to tell you they sound awesome, and I feel so much of this is being driven by your amps. I have included
a few pictures of my system. Everyone who hears the combination your amps and Decware speakers are just awed by the speed
and clarity of the system. Once again... my highest compliment to you! Great Job." - Bryan
There are 300B SE DHT amps, then there is WE91A 300B. The sound of these giants are as good as they can get. I got the first
taste of the design through my WE91A Stereo, and I was hooked. I said to myself, "seriously, why build anything else?". These monoblocks actually use 6J7s,
which are pentodes, for drivers. The schematic that I used for this amp is also very clean - it does away with hum balance
pots and use filament windings for the 300B's bias. I also increased the capacitance, as much as the 5Z3 will allow, which
was 30uf-50uf-30uf. The power supply is really where these amps shine. All ASC oil caps with a heft choke in C-L-C-R-C
filter network. Result? These are the quietest 300B amps I've built so far, even with my 99 dB/W/m Klipsch Forte Is.
As you can see, I am going for the 1930's industrial look here, consistent with early WE amps. The tranny bells
are enamel coated, baked in oven for curing. These blocks are pretty hefty, thanks to those massive transformers.
I am all about not using PCBs, if I can help it. It's also my belief that the best sounding amps can be had through handwiring.
This is mostly because it really showcases the builder's ability. These amps are as pretty on the outside as it is in
the inside. So, how does it sound. Magical! If you're suffering from headaches and listener's fatigue associated with
bad sound, these will be almost therapeutic for you. The liquid smooth mids and highs, complemented by tight, controlled bass.
These are must for those that like to listen to classic jazz on vinyls. Having said that, these sound great with
rock, big band, pop, and whatever. They can handle it. All that for under two grands, it's a steal!
Bryan's system, a current owner of these monoblocks. He seems to
be pretty happy with the amps driving those Decware fullrangers (look at his feedback).