The Circuit: A guide to Fender’s glorious Fifties amp models

Fender made 10 different tweed models, and each went through various changes during its lifespan.
By cscapelliti,


By Mitch Colby | Illustration by Evan Trusewicz

Fender defined state-of-the-art guitar tone for many years, starting in the late Forties. When it came to amps, the period from around 1955 through 1968 was the company’s golden era. From sparkly Tele-laden country to roots rock and humbucker-driven blues, Fender amps set the stage. In this column, I’d like to acquaint you with some of the distinguishing features of these most collectible amps.

A comprehensive Fender amp collection should include woodies and tweeds as well as blonde, brown, and blackface models. The tweed amps, in particular, are prized for their tone. Early tweed amps used octal tubes, and while octals sound good, it is generally tough to find metal octals, such as the 6SC7 tube, that are not microphonic. Fortunately, glass bottle octal tubes, like the 6SN7, tend to be fine. Most other tubes used in early tweed amps are relatively abundant in today’s market.

Fender made 10 different tweed models, and each went through various changes during its lifespan. For example, the tweed Super has at least eight different schematics. The four- and five-watt Champs and Princetons are Fender’s only Class A single-ended amps, both using a single 6V6 for power. The two models are basically the same, with Champs sporting a lone volume control and Princetons having volume and tone controls. The Champ started out with a six-inch speaker but later graduated to an eight-inch, while Princetons have eight-inch speakers. Both are great for recording, due to their harmonically rich tone and low-volume crunch, which has been heard on countless records.

The Harvard is a great amp, with 10 watts of output due to the use of two 6V6s in a push-pull configuration, and a 10-inch speaker. Add tremolo and you have the Vibrolux. The Harvard and Vibrolux are two favorites of mine. They are great living-room amps and sound warm and satisfying with overdrive pedals.

The Tremolux is basically a 15-watt Vibrolux with a 12-inch speaker, although the phase-inverter circuits are different. That’s not surprising, as Leo Fender experimented a lot with tweed circuits. Fender amps feature three different types of phase inverters: paraphrase, cathodyne, and long tail. These circuit differences have an effect on the tone and feel. The cathodyne phase inverter is a little more forgiving and distorts easier. The long-tail phase inverter has a touch more clean headroom and is used in every brown, blonde, and blackface amp. You will also find fixed- and cathode-biased tweed amps as well as those with and without negative feedback.

The early Deluxes are nice, but the later 5E3 narrow-panel amps are the most desirable, partially because of the switch from octal to nine-pin miniature preamp tubes (12AX7/12AY7) and the cathodyne phase-inverter circuit. The channels on these amps are interactive and produce quite a variety of tones. A Deluxe puts out around 15 watts, and with its relatively low-efficiency stock speaker, it isn’t quite loud enough to cut through a band with a loud drummer.

The above amps feature ingenious tone control circuits. The single tone control acts as a treble boost in one direction and a treble cut in the other. For treble boost, a small capacitor is bypassed across the volume control similar to the way a bright switch works on blackface Fender amps, but here the tone pot controls the amount (with the volume on full, this will have no effect). In the other direction, there is a larger capacitor that is shunted to ground, which reduces the amount of highs as you turn the control toward zero.

The Super, Pro, and Bandmaster (all around 30 watts) in their various iterations are basically the same amp circuit with different speaker configurations. The Super has two 10-inch speakers. The Pro with its 15-inch speaker is a favorite of many players, especially the narrow-panel ones with the presence control. The Bandmaster, with its 3x10-inch speaker configuration, is highly collectible because of its rarity.

The 4x10-inch Bassman is a formidable 40-watt amp. Used mostly by guitarists, the 1959 and 1960 5F6A Bassman amps are tone machines that provide great cleans and thick overdrive when cranked. The Bassman was one of many amps in Stevie Ray Vaughan’s arsenal, and the 5F6A circuit was the basis for most Marshall and high-gain amps that came after. Low-powered Twins are great amps too, and feature circuits similar to the Super/Pro/Bandmaster with beefed-up power amps and speakers. The high-powered Twin is essentially an 80-watt Bassman with four 5881 tubes. The clean tone is glorious, but larger and warmer than a Bassman. The 80-watt tweed Twin is a Keith Richards favorite.

Mitch Colby helped develop many Marshall and Vox amp designs and is the founder of Colby Amplification.

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