The journey of a thousand miles begins with a single step. Our journey shall begin with a trip to our local library. Why? Because it is far cheaper than actually paying for books ourselves. Which books? There will be many. We will teach ourselves about life as it was many years ago, as this pertains to our quest for tone truth. You will learn much more than you’d imagine from books about woodworking, machine shop practice, and even business practices! I’ve lately taken to reading science books aimed at my children! The projects may seem juvenile, but they have given me a lot to think about, and are a great way to remind myself that there are basic fundamentals behind everything in life, including guitar amplifiers. Besides, if you don’t know too much about magnetism (as one example), ‘beginners’ books are the only place to ‘start’, unless you want to jump right into college texts and determine the flux density and permeability of a piece of sintered Alnico. Other books of extreme importance will include vintage electronic theory tomes, which we will have to purchase, but this is well worth the expense. Unfortunately, even the best of the classic theory books won’t have all of the answers. An example would be the difference in gauss density between a 16 oz. sintered Alnico magnet and a 16 oz. cast Alnico magnet. This is where experience is the necessary supplementary ‘teacher’. The best advice I can give you here is to also find at least one ‘old-timer’ in your area. Someone who was a radio repairman in the golden era of tubes, or a ham radio operator during the 30’s or 40’s. These people were ‘there’, experimenting with audio when it was ‘young’, and have a lot of knowledge and experience to share with us all. I’ve formed a local group of ‘old-timers’ that I meet with regularly, to ask of their knowledge and experience. They are glad to know others of their ilk are still alive, and for the price of a few lunches I learn more in two hours with them than you would spending two hours surfing any web page, including my own. Let’s go back ourselves, and see what it was like for the pioneers of tube audio. Always remember the mindset of manufacturers during the Great Depression and WWII was never to build the ‘best’ product possible. There are harsh economic realities to consider.
If you were able to go back in time and ‘invent’ the electric guitar amplifier, which era would you choose? Be careful in your selection. Should you decide on the 1920’s, remember that all amplifiers of this time were used exclusively for voltage amplification. High gain tubes are not available. Neither are 6L6’s. You are ‘stuck’ with 2A3’s. A single 2A3 triode output tube yields about 3.5 watts of audio power, and was considered more than ‘enough’. 2A3’s also ‘spoiled’ a lot of audio men, who didn’t like the pentodes that came out some time later. Sure, pentodes had a lot more gain (and many early tube developments were the direct result of a quest for more gain), but also a lot more distortion, because of a poorer ‘damping factor’ in the common circuits used during the early days of tube electronics (feedback circuits came about much later). During the 1920’s RCA ‘owns’ all of the important receiving tube circuit patents, as well as controlling interests in other tube patents jointly shared with General Electric, Western Electric, and Westinghouse. Their monopoly controls the price of vacuum tubes. RCA also has an army of spies, watchdogs, and corporate lawyers looking out for patent violations. RCA is the quintessential ‘bully’, and loved to sue small companies and large corporations alike.
When color-television was being developed, RCA sued other TV manufacturers such as General Electric, Motorola, Philco, and Westinghouse. RCA was also embroiled in bitter, lengthy court battles with ‘inventors’ like Edwin H. Armstrong and Lee deForest! Even the fabled tweed covered Fender Bassman amplifiers into the 1950’s still had a little sticker inside the cabinet which read…..”Licensed under U.S. patents of American Telephone Company & Telegraph and Western Electric Company, Incorporated, for use only in public address systems, …systems for distribution from radio broadcast receiving sets or musical instruments…”. Take two guesses as to whose vacuum tubes Fender used throughout their early years (and not because they had ‘the tone’!). RCA forced you to license a circuit design from them and pay royalties. And pay. And pay…
Even as you approached the 1930’s, you have other mountains to climb. Many manufacturers pushed the idea of an electric guitar in their catalogs, but they were looked on as toys or gimmicks. Jazz players preferred the tried-and-true formula of an acoustic guitar buried behind the trumpet player. Blues players? I’ll wager that the thought of carrying an extra piece of equipment on your back as you try to jump onto a moving train isn’t very appealing. Also, too, keep in mind the luxury of having hydroelectric or AC power in these times (most radios were powered by three batteries). And let’s not forget The Great Depression! This caused the many radio manufacturers who didn’t succumb to the high licensing fees and harsh economic times to totally rethink their approach to manufacturing and advertising their wares. Examples include the Charles A. Hoodwin Company, of Chicago, who would advertise their 1932 ‘Aero 4-Tube Set’ as being ‘…equal in performance to last years’ 5-tube set’. In other words, the parts count was kept as low as possible. Also worth noting was the necessity of developing a dynamic speaker where the field coil received its’ voltage by doing double duty as the power supply’s filter choke. Thus, the manufacture could eliminate the expensive and bulky choke, reducing the radio’s size and cost even further. This was also the time when the design of the AC/DC radio was developed, eliminating the need for a power transformer! This really knocked down the prices, and could also be pitched to people who had AC or DC service to their homestead. The people who had DC service and wanted to purchase an AC appliance had to buy a rotary converter, adding an additional expense to any purchase proposition.
Many U.S. homes and warehouses did not have AC electricity, even into the 1950’s.
No, I sure wouldn’t want to pick the 1920’s or 1930’s to unleash my electric guitar amplifier on the world. The 1940’s are a little friendlier. Your favorite 6L6’s, and even 6V6’s, are around. 6V6’s are developed in the era of the 6.3-volt heaters (not coincidentally the same voltage as a car battery), but as a low current tube for use in single-ended cheap automobile radios! They were conceived with battery drain the prime criterion, and not tone. 12AX7’s are born in 1948, but the first ones have heater construction problems. They were prone to hum pickup, not good for audio. Philips realized this, and developed the ECC83, a vastly superior tube. RCA had to develop the 7025 in response, but this is not pertinent in 1940, though. Early 1940’s preamp tubes include the 6SJ7 pentode and 6J5 single triode or 6SC7 dual triode. The whole lesson here is that as a designer, you can’t just belch out …”Gimme a pair of 6L6’s and a few 12AX7’s and I’ll invent the sound of Rock ‘N’ Roll!” You must be aware of what tubes are available/common to the times. Not all tubes were designed at once, and most engineers will stick to just a few that they are familiar with. Many electronics magazines and books (such as the much-ballyhooed Radiotron Designer’s Handbook) will ‘teach’ you circuit topology featuring the favorite tubes and circuits of the day. RCA tube manuals will supply sample circuits much like flour bags supplied pancake recipes, and these circuits will be used verbatim in early Fender (and others, to be fair) amplifiers. A very few early guitar amplifier manufacturers who decided not to license RCA circuits would hire an ‘outside’ designer such as Lyon & Healy to come up with a ‘safe’ amplifier circuit. Companies like Gibson, Gretsch, and Harmony have used Lyon & Healy circuits.
Not all tubes were developed on the same Friday afternoon, so a designer could pick which ones he’d like to use for Monday morning.
This little bit of history is needed to make you aware that there was a lot going on in the background of the early 20th century. While marketing your new amplifier you must take into consideration patent licensing, tube prices, who has AC power, etc. The Great Depression and WWII are just around the corner, and this will greatly influence the mindset of all manufacturers. I have only barely touched on the issues. You will do further research on your own at your local library. Please read the following books;
- A Streak of Luck-The Life and Times of Thomas Alva Edison (Robert Conot)
- Tesla-Man Out Of Time (Margaret Cheney).
- 70 Years of Radio Tubes and Valves (John W. Stokes).
- Empire of The Air-The Men Who Made Radio (Tom Lewis)
These books should get you on track to understanding how things were many years ago, as they pertain to the electronic/electrical world. Keep in mind too that the amplifier designs we all covet today were circuits derived at the tail end of the tube era. The very first amplifier designs would not be considered as having ‘the tone’. Distortion is frowned upon, as the amplifier is seen as a reproducer of sound, rather than a producer of a sound quite different from what went into it!