My first exposure to real high fidelity came when I was about 6 or 7 years old. My grandfather, an electrical engineer in the Detroit area, had put together a "HiFi". He built the furniture, and friend had assembled the kits. The amps here are surviving examples from that era, around 1957. What amazed me was that the turntable and electronics were housed in a beautiful white cabinet on one side of the living room and the large Electrovoice speaker was on the other side. Whoa. Cool. Then he played Elvis Presley on this rig and I was blown away. Of course I knew how Elvis sounded on our typical record player at home, but this was huge! Another favorite was a Tweetie Pie and Sylvester record with all the sound effects and the suffering succotash sprayed all over. After he passed, I ended up the W3M, the WA-P1 preamp and the speaker in my room. I learned about HiFi electronics with this equipment. The original equipment has been long lost, but I found 1 W3M and WA-P1 online several years back and have displayed them in my audio room as a nod to the heritage. But here's the fork in the road: I found another amp on eBay for a reasonable price, although not in as good condition as my showpieces. So, after reading more about the Williamson design and the Acrosound transformers, why not rebuild them with modern components and put them to work? Then, inspired by the Velocity Channel TV show "Overhaulin'" why not hot rod to a new level? A dream pair of monoblock separate chassis amps that have plenty of power for either the lab or for the main system!
The top 2 pictures are the ones I picked up awhile back, the third is the newer acquisition. These chassis have some significant rust on the bottom, but the transformers look good.
First thing I did was to verify the transformers are good, then completely disassembled them (fourth photo). Resistance measurements were made on all resistors, and although some retained their original values, others were way off. I even discovered an intended grid resistor on the driver tube connected to the plate! I'm wondering how that thing even saw service! So resistors must be replaced. Since I am going for an updated sound, I am toying with the idea of replacing all resistors with modern metal film. Power supply can electrolytics in the 1" diameter size are not available anymore for the PS unit. There is a suitable electrolytic cap available for the amp chassis. So the PS chassis will retain the the old caps just for looks with modern axial caps doing the work below. I also plan to use film bypasses on the electrolytics. I haven't decided on coupling caps yet, but my friend John Stein is a fan of Jupiter Beeswax types. If they fit, I'll likely give them the nod based on his ears. Of course all new tubes as well.
You might notice in the photos that the amp chassis are slightly different, Photo 5. One uses clamped- on octal tube sockets and the other uses sockets that are affixed with screws. Since this is a custom rod, I was thinking they should look the same, so I wrestled with several ideas all involving some non-ideal trade. After listening to my whinings, my wife suggested that I rebuild each with its correct socket, reflecting the actual production changes that occurred for this model. Why didn't I think of that? Done!
~~Photo 6 ~~The bottom covers have the worst rust so there may be some Bondo in their future. Photo 7 shows the chassis with the paint removed and most of the rust sanded down. The "Hot Rod" paint scheme will be conservative: dark gray metallic with clear coats for the chassis, gloss black for the power transformers and choles, and as-original-as-possible for the Acrosound output transformers, which is a silver hammertone. These might polish up, so possibly even THE original paint. We'll see. This color scheme will keep the original industrial feel, but will be classed up for living room exposure.
They're essentially done. Well, except for playing around with them.
Chassis and transformers were primered and painted, sometimes more than once! Dark gray on the chassis turned out well, but I elected not to polish them, only the power transformers and chokes. The Acrosounds had to be painted twice because I didn't like the look of the hammertone. I think plain silver metallic looks much better against the dark gray.
Electrically the units were changed a little bit: 3 prong power cord, larger gauge interconnect cable, on-off switch, large speaker binding posts and the elimination of the current sense 1/4" phone jacks which were is series with the output tube current. Bias balance is now set by reading the voltage at the top of a hard wired fixed 10 ohm resistor directly connected to the cathodes. Since these resistors are matched, and the main cathode resistor is common, the voltage at the top of the 10 ohmers indicate the current through each, hence through each output tube. All carbon comp resistors were replaced with either metal film or carbon film. Currently running RCA tan base 6SN7s (actually one is a 5692) for the input/phase splitter tube, Russian 6SN7s for the drivers and Svetlana(Winged C) 6L6GC's for output tubes. I'm running off the 4 ohm tap. Still breaking in, but starting to sound real nice.