Wouter Vriesman is a client of my friend, Marlies Vonk of Oirschot,
Netherlands (www.marliesvonk.com). <view her site in
When he went to her atelier to view his commission, music was playing from the amp that I built for Marlies and Ton.
He was so impressed that he had to have one for himself. This is what I built for him for his home, a houseboat near Amsterdam.
This is yet another version of the proven WE91A circuit from the mid
1930s. Again, the red color is by far the most popular.
On this amp I used the James 6123HS output transformers, same as on my silver amp. I have found these
transformers to be of excellent quality, very nicely constructed and expertly potted in metal cans. Since
they come in a champagne color and the client wanted a red amp, I was forced to paint the transformers
to match the powder coating done on the chassis and transformer end bells. I used a custom-mixed automotive
lacquer to paint the transformers. It wasn't easy, but it turned out very nicely, IMO.
Wouter wanted to use a good quality 300B, something better than the
Russian and Chinese tubes you see so
often, so I chose the Emission Labs 300Bs. These are hand made tubes from the Czech Republic. They are available
in the US from TubesUSA.com. Not inexpensive, but very high quality. Give George a shout and he'll get you fixed up.
Other tubes are NOS 5Z3 rectifier and NOS 5693 pentodes.
Here's a shot of the amp from the bottom.
I sourced Hammond filament transformers, the 266 series with
117/234V primaries, and chokes. I also used the *big* Hammond
power transformer, the 378CX with the dual primary windings. The physical size of this transformer caused me to squeeze the
amplifier section into less space to accommodate it. That's why I decided to use the different arrangement for the location of
the 5693 driver tubes.
Power supply filtering in this amp is accomplished with motor run
capacitors designed for air conditioning service paralleled
with a 100uF electrolytic. They are rated for 370V AC and are non-polar. They are good to at least 500V DC, and see
only around 400V in this amp, so they should last a long time. I have yet to have a failure with one.
When I sanded the James transformers prior to painting, I was
surprised to find that one had grey primer and the other
one had black. Here's some before and after shots showing the transformers as new (well, almost new) and after painting.
I think they look pretty good.
Painting with lacquer requires a lot of wet sanding with waterproof
sandpaper. I did the initial sanding with 400 grit and I also
used 400 grit on the primer and first sanding of the finish coat. It must be sanded until the surface is completely "flat", with
no sheen at all. Then, it's fairly quick to do the remaining work with 600 grit, 1000 grit and a final 2000 grit samding to bring out the shine.
The finish is then polished with red rubbing compound, white polishing compount and finished with automotive paste wax.
Here's a shot showing the rear of the amp.
You can see that I drilled holes for each RCA jack instead of using
a board of pre-mounted jacks. I like this much better.
You can also see that there are two fuse holders. The lower one is for the mains fuse and the upper one is a fuse in the B+
to remove power in the event of a tube runaway or other fault. I learned about that the hard way on my silver James 300B amp.
The speaker terminals are well made and were bought from a shop in Hong Kong through ebay.
Click the link below to see the 91A schematic.
If you have any questions about this amp, if you would like further information, or for any other reason, please email me at: