1950's valco 51 tube amp
vintage valco amp finds a new home along with a cap job and a new cabinet.
One day a forlorn old Valco 51 was headed to the dumpster. Along the way it fell into my lap. It was merely a chassis and a speaker, still connected and without a cabinet. Sporting "chicken-head" knobs I estimated this amp to be from the 1950's. One man's trash is another man's treasure. I figured if I could get this old thing working with a minimum of fuss it might have a nice vintage tone and be worth the effort.
Plugging the amp into AC and powering it up produced nothing but a loud hum. The old capacitors had given out long ago. This is common as capacitors degrade over time until they eventually fail. My dad has alot of experience with old tube amplifiers. He was stationed in post-WWII Japan as a Navy radio technician. He was able to help me diagnose the amp over the phone, and through the process of elimination helped me track down which capacitors were the source of my problems.
Replacing all the failed and/or failing capacitors in an old tube amp is often referred to as a "cap job". I figured if I could give it a cap job and get it to work I would make a custom cabinet for it. At the time I had a small workshop in my basement and I had time to tinker with weird old stuff.
Brightly colored Sprague Orange Drops are a quick visual indicator of an old amp with a fresh cap job.
I made a list of the values of the old paper capacitors I would need replacing. Sprague Orange Drops are a polyester/polypropylene film capacitor long admired as the premiere replacement capacitors for guitar and amplifier applications. Orange drops do not deteriorate like the old paper capacitors do. An electronics technician friend and a local luthier who makes custom amps supplied me with the replacement capacitors necessary to get my vintage amp working again.
The preamp section amp is powered by an RCA 6J7 and a 6SC7. At first I was perplexed as these two tubes have metal housings as opposed to the more common glass preamp tubes used in more contemporary guitar amp applications. I would learn that the 6J7 was one the most utilized voltage amplifier tube in studio and broadcast industry from the late 1930's to the mid 1950's before the advent of the smaller "all glass" EF86. My 6J7 includes a top-cap connection for the control grid. A later version, type 6SJ7, dropped the top cap in favor of its control grid connection on pin 4.
The truly vintage RCA 6J7 tube includes the unusual top-cap connection for the control grid.
The power amp section uses two 6V6GT tubes to output around 18 watts. The 6V6 is a beam power tetrode, used in single-ended class A audio output stages of radios and sometimes seen in class B audio amplifiers.
This project started pre-internet and I didn't have any visual clue as to what the original cabinet would look like, but I figured I would go retro with an asymmetrical design reminiscent of old Gretsch amps. Ironically I would learn later that Valco made many of the early Gretsch amp back in the day. My luthier friend suggested I use solid pine for the cabinet like old Fender amps. He preferred solid pine cabinets saying that they resonate musically unlike cabinets made of dense particle board. I took his advice, finger-jointing all the corners in the process, and used half-inch ply for the front speaker faceplate and rear covers. It's now my main amp for dinking around on project guitars.
The cabinet is constructed of soild pine and half-inch plywood. One day I'll get around to covering it in a nice two-tone Tolex™ color scheme.
While the amp sounds sweet I still have some work to do ... mainly finish some trim on the face, then cover it all in Tolex™. But I use it occasionally as is. Considering where it once was headed, I'm happy to use it despite the lack of Tolex™.
a brief valco history
In the 1940s, Valco was formed by three business partners and former owners of the National Dobro Company; Victor Smith, Al Frost, and Louis Dopyera. The company name was a combination of the three partners' first initials (V. A. L.) plus the common abbreviation for company (Co.).
Valco manufactured Spanish acoustic guitars, metal-faced resonator guitars, electric lap steel guitars, and vacuum tube amplifiers under a variety of brand names including Supro, Airline, Oahu, National, and others. They also made amplifiers under contract for several other companies such as Gretsch, Danelectro, Harmony, and Kay. In the 1960s they began producing solid body electric guitars.
Valco merged with Kay Musical Instrument Company in 1967, however the merged company quickly went out of business in 1968 due to financial difficulties.
A casual search of the internet netted me the following interesting photos. A guitarist was reluctantly selling off some vintage gear on eBay to pay for medical expenses. The seller claimed this was a 1955 English Electronics (Valco) Tonemaster. While the basic configuration can be found in various models under various brand names, this particular brand features a control plate that most closely matches my old amp.
