JBL: JBL speakers were optional (at additional cost) for nearly all models from 1960 to about 1980. JBL D-series speakers had orange baskets and Fender by JBL labels in the 1970s. JBL D-series speakers can generally handle upwards of 60 watts each. A pair of JBL D-120Fs in a Twin Reverb are only seeing about 40-watts each (no sweat), but remember that no speaker likes to see square waveforms. So, driving the Twin with any amount of distortion lowers the power handling capacity of the speaker, which makes any speaker more susceptible to damage; even a high-wattage type like the JBL.
Jensen: Jensen was the prevalent stock speaker in Fender amps from 1946 through about 1961. As the story goes, Leo Fender wanted Jensen to make some changes to speakers and either the speaker couldn't (price constraints?) or wouldn't do so. That's when ol' Leo switched over to Oxford as the standard speaker (though Jensens were still used from time to time). Just conjecture, but the lack of orders from Fender from 1962 - 65 must have hurt Jensen's pocketbook so they hit up the new owners of Fender (CBS) for some business. These Jensens wear brown and gold Fender by Jensen label and were put into Fender amps beginning in late 1965 through about mid-1967. Some amp geeks don't like the way these Fender label Jensens sound, but let your ears be your guide. I think they sound just spiffy.
Jensen Vibranto LI and MI series speakers (alnico magnets) and Jensen EM-series speakers (ceramic magnets), while excellent, were not used by Fender. I have included them here because I get a lot of questions about them. They are were often sold as replacements for blown speakers which is probably one reason why the ended up in more than a few Fenders. The Vibranto LI series speakers had a lifetime warranty and it seems that Jensen went out of the musical instrument speaker business just in time to avoid the claims. All speakers can and will fail eventually (just like the hard disk on your computer); remember that.
Jensen speaker models denote their approximate power handling capacity and magnet type. The actual power ratings have been published in several books so I'll discuss them in general terms here.
The R, S, and T suffixes denote a low power rating: good for Princetons and Champs, but the R is barely able to handle the power of a Deluxe. The Q and P suffixes denote a medium power rating. These are especially good for multi-speaker amps up to 40-watts since multiple speakers divide the amp's total output power between them. For this reason, the P10Q is the speaker to have in the 5F6-A Bassman. Note that it does not appear that Fender used the "P" rated speakers very often. The N and LL suffixes denote a high power rating, with "high power" being a relative term. The P12N, on a good day, can handle 20 watts. It's no wonder that 80-watt Twins easily shredded a pair of them. Note that Fender did not use the "L" rated speakers (but Ampeg and Leslie did).
Oxford: Oxford speakers codes work in a similar fashion, but it is the letter that denotes power handling. The higher the letter, the higher the power rating. I found an Oxford ad in a 1960s trade magazine with the peak power ratings of some speakers: K = 25 watts, L = 30 watts, M = 40 watts, and T = 45 watts (12" speaker) or 60 watts (15" speaker). It is important to note that these are peak power ratings, not RMS power. The RMS rating is more realistic and is usually about half of the peak rating so use that as a rough guide.
The "J" rated speakers are usually found on 12-watt Princetons. The "K" rated speakers are found in reverb and non-reverb Deluxes and in multi-speaker amps up to 40-watts such as the Tremolux and Concert. The "L" rated speakers are found in reverb and non-reverb Deluxes, some Tremolux amps, and multi-speaker amps like the blackface Concert, Super Reverb and Vibrolux Reverb. The "M" rated speakers had good service life in the piggyback Bassman and Bandmaster amps, but were easily blown in blonde Twins. The "T" rated speakers were standard in Twin Reverbs, but like the Jensen C12Ns, they often had a short service life.
Many amp geeks don't like Oxford speakers found in Fender amps from 1965 through the 1970s. The gap distance was increased in the Oxfords that Fender used later in the decade and this reduced their efficiency (and they were cheaper to make this way). Again, I say let your ears be your guide. I've heard many great sounding Fender amps with Oxfords. I will admit that I prefer Jensens, but I've never let an Oxford speaker sway my decision from owning a Fender amp. Additionally, the Oxfords from early '60s generally sound very good. According to noted vintage amp specialist Gregg Hopkins, these early Oxfords were constructed similarly to Jensens from that period with respect to materials and voice coil gap. That could explain why they sound good.
CTS: CTS (Chicago Telephone Supply!) speakers were used occasionally in Fender amps until the mid-1960s. These are good quality speakers that tonally lie between Jensens and Oxfords. The alnico 10-inch CTS speaker was the most prevalent speaker in Super Reverbs from the mid-1960s through the 1970s.
Utah: Fender didn't use Utah speakers very much until the 1970s. The Utah speakers from the '50s sound very good and I've heard a killer '66 Super Reverb that was equipped with factory original Utahs. Generally, the Utah speakers of the '70s weren't as great sounding as their predecessors, but again let your ears be your guide. If you like the way your '75 Twin Reverb sounds with its Utah speakers, just leave it alone and go right on playing. Utah went on to become Pyle of Radio Shack and car audio fame.
Eminence: Eminence has its roots in CTS (Mr. Gault left CTS to found Eminence) and many of the early Eminence designs are similar or identical to CTS speakers (good examples of the similarities can be found in mid-1970s Ampegs). Fender began using Eminence speakers as standard in nearly all of its tube amps beginning in the early 1980s. These are generally made to Fender's specifications and in some cases, such as the reissue '65 Twin Reverb, the speakers were designed to emulate the Jensen C12N speakers which were often found in the original '65 Twin.
Rola: Yet another speaker that Fender used in the mid to late 1970s was Rola.
So in technical terms, why don't the non-Jensen speakers from the mid-1960s through the 1970s sound as good as Jensen speakers? Speaker guru Ted Weber explains:
"Utah, CTS, Oxford, etc. simply copied the Jensen designs and started competing for Fender's business. As a result of the price wars, they had figure out how to make the speakers produceable with a very low reject rate as well as use less expensive parts, i.e. smaller magnets. So, they widened the gaps to make them easier to throw together on a fast assembly line. This lowered the energy, so the voice coils were shortened to compensate. The companies also needed to produce speakers with long term reliability, so they doped the surrounds. The end result is that with some of these speakers you get a relatively sensitive driver that sounds great at lower volumes, but falls apart when you push it -- flabby on the low end and/or harsh on the high end."
Replacement speakers: It is very common to find non-original speakers in Fender amps made up through about 1980. Because reconing wasn't a common option until the 1970s, players simply replaced the speakers if they blew up. In some cases, such as Altec and JBL, the factory would recone a speaker. Today, reconing is a very popular option for players to keep their amp's speakers original. Reconing must be done correctly and with the right parts so stick with a reputable reconing service that offers a warranty. In most cases, the reconed speaker will sound nearly as good or as good as the original. In some cases, the speaker will sound even better. The reconed Oxford 12K5 in my Deluxe Reverb sounds better than any original cone 12K5 I've heard.
There is a strong market for used speakers. Many times a player can find an original speaker to replace the non-original speaker. Another option is to install vintage style speakers. Jensen has reissued the C10Q, P10R and P12N and WeberVST makes many models of Jensen-style alnico and ceramic speakers.One final note before you scope out the speaker chart -- there are exceptions to every rule and this especially applies to Fender! So, if you see a factory stock P12P in a tweed Deluxe, don't be overly surprised.
Alnico vs. Ceramic Magnets
Alnico magnets possess a certain buzz in the speaker world (and also in the world of guitar pickups), and are considered to be a more “musical magnet” that’s revered for sweetness and dynamics. Alnico is an alloy of aluminum, nickel, and cobalt (blended with a quantity of iron). Thanks to the relative scarcity and expense of cobalt, it’s an expensive alternative to the ceramic magnets that are also employed in speaker manufacturing, and alnico was all but dropped from use in the 1970s and ’80s. While this description of alnico implies a certain superiority, be aware that several classic speakers—even many vintage models, and those that remain the driver of choice for countless major players and tonehounds—were (and continue to be) made with ceramic magnets. Celestion’s G12M Greenback and G12H-30 are both ceramic speakers, as are plenty of great units from Eminence and revered early to mid-’60s Jensens.
When we talk of speaker distortion, we mean a form of distortion—distinct from amplifier distortion—that is generated when a driver is pushed near its operating limits. The voice coil and paper cone begin to fail to translate the electrical signal cleanly, and, as a result, produce a somewhat (or, sometimes, severely) distorted performance. Put simply, the voice coil begins to saturate, the paper cone begins to flap and vibrate beyond its capacity, the magnet’s performance compresses, and the entire electro-mechanical network that makes up a speaker cooperates to bring its own degree of fuzz to the brew. The concept of such distortion is sometimes confusing, because it often occurs on top of any distortion the amplifier itself is producing. The distortion produced by a high-gain preamp stage—or a floored output stage—can occasionally be heard on its own when an amp is played through high-powered speakers that refuse to distort (or distort very little), even under high-output conditions. In most cases, when an amp is raging, you’re hearing a little of both.