Guitar amps are wonderful, mysterious things. Like any other amplifying or processing device, guitar amps impart varying degrees and types of coloration to the input signal, and can have character that informs artistic or aesthetic choices. The cooler ones beg to be used unconventionally to exploit their quirks and character — even on non-guitar sources. While there are many great names in guitar amp history, there's probably none more ubiquitous and intriguing than Fender — the company's colorful history is full of cool amps. Prior to 1980, three broad categories emerged that have distinct sonic and cosmetic identities: tweed, brown/blonde Tolex and black/silver panel. To learn more about the sounds these amps offer, let's break each era down into parts: preamp, power amp, speakers, power supply, cabinet construction, and finally, onboard tremolo and reverb effects.
Tweed amps were produced for well over a decade, and evolved considerably over that time. Early tweeds have rounded "TV Front" grilles and primitive electronics. These evolved into a design with wide panels above and below a rectangular grille, and finally into the most common (and sought-after) version: the narrow panel amps.
Preamp: As a result of constant evolution, tweed preamps are a mixed bag. Some of these earliest amps have grid-leak biased preamp tubes, while later ones use the more typical cathode bias scheme. Grid-leak is a primitive bias method that doesn't tend to handle hot input signals very well — be careful when running boosted or line-level signals in some of the TV-front amps. Smaller tweed amps have simpler tone controls than the larger amps, and many have interactive volume controls. The narrow panel tweed Deluxe is one such amp — changing the volume control's position on an unused channel will affect the other channel, and the tone control behaves differently depending on the channel used and where the volumes are set. Experiment with this! There are a lot of tonal possibilities to be explored. Medium-to-large narrow panel amps (Pro, Bandmaster, Super, Bassman, etc.) make use of a cathode follower after the tone stack. As a result, the tone controls behave a bit like overdrive controls — when bass and treble are turned almost (but not fully) all the way up, the hot output from the cathode follower will overdrive the phase inverter and power tubes. Use this to your advantage! After 1960, Fender abandoned this topology. In tweed amps with multiple channels, all channels are "in-phase" with like electrical polarity. Consequently, in four-input tweed amps, a short cord can be used between inputs to "bridge" the channels, encouraging earlier distortion.
Power Amp: Three phase inverter designs show up in tweed amps. Some early tweeds have the primitive paraphase style. Later, Fender employed the cathodyne style in small-to-medium amps like the Deluxe, Pro, Bandmaster, and Super. Larger amps like the Bassman and the Twin use the long-tailed-pair inverter. Each style has its own sound — the long-tailed-pair has a smoother, more controlled overdrive than the cathodyne style, which can be wonderfully raw and loose when driven into distortion. Small-to-medium tweed amps (Champ, Princeton, Deluxe, some Harvards and some Tremoluxes) use cathode-biased, or "self-biasing" output stages, while the larger tweeds are fixed-biased. Cathode-biased output stages offer a spongier envelope and a bit of natural compression or "sag" to the notes that is often flattering. Fixed-bias amps, as a rule, offer a firmer feel with tighter bass and a robust attack. Most tweed amps have very high-quality interleaved triad output transformers that contribute to the amps' sonic signature. When shopping, avoid paying a lot for a tweed amp with non-original output iron. Finally, most tweed amps are designed with less negative feedback than their later counterparts. This contributes to the raw, touch-sensitive feel for which tweed amps are known.
Speakers: Once permanent-magnet speakers became available, all tweed amps came with AlNiCo-magnet speakers — commonly Jensen, but occasionally from other manufacturers. AlNiCo speakers offer their own natural compression. When the voice coil moves, it creates its own magnetic field that temporarily demagnetizes the AlNiCo a bit. This results in a soft-knee compression that is most noticeable at high volumes.
Power Supply: All tweed amps are tube-rectified, and tube...
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