Disclaimer - (1) I know next to nothing about this. I enjoyed my PRII with the factory speaker in it. Do I really prefer the replacement I fitted, or do feel I ought to simply because of the time and money spent? I think there's a genuine improvement. And others quoted below clearly aren't kidding when they rave about their new speaker. But you choose.
Disclaimer - (2) This is all subjective and none of my contributors is claiming that any brand of speaker is badly made or poor value for money, so please don't sue them or me.
Disclaimer - (3) Because this is so subjective, please do not blame me if you spent as much on some legendary speaker as you did for the whole amp, and then found you liked the original speaker better. However, your opinion might be worth repeating here if you think others may be similarly disillusioned.

I have replaced my original speaker with a Jensen C12N reissue (Sep 04). After a couple of rehearsals with my band, here are my impressions. Compared to the original, it has more sparkly top end, more bass, and little more efficiency. At low volume (say master = 3 ) this speaker is louder than the original. At higher volumes the cone breaks up earlier, providing speaker distortion at lower volume than the original. At the max volume I don't think this speaker is louder than the original, due to cone breakup and (I think) the mild compression effect of the ceramic magnet. In general the sound is a little more detailed and 'organic' or 'natural'. The cheap power valves (which I had in the amp most of the time) used to sound a little nasty when pushed into distortion, but this speaker somehow makes them sound OK.  It took 2-3 hours of playing at medium volume to 'break in'.

I didn't think the original speaker is the dog which some folks make it out to be. But the Jensen improvement is worth the $45 (30 GBP, 2004) I paid South Valley Vintage Amps in Gilroy, California, USA (warmly recommended outfit). Knowing what I know now, I don't think I would have paid $100 for this kind of improvement, but that's just me and my Scottish heritage showing through.

With the original speaker I used to get a pretty natural-sounding acoustic sound from my Yamaha acoustic with a Martin piezo pickup. It's not so natural with the Jensen! Can't win them all... maybe this says the original speaker was deliberately chosen for a neutral sound in order to make the amp as versatile as possible. (Obviously I don't mean Fender intended the amp it for acoustic amplification, but I don't believe they chose the speaker carelessly, as some folks seem to suggest.)

Technical bit
The PRII puts out 22W RMS, expects an 8 ohm speaker, and is built for a 12" speaker. The original speaker was rated at minimum 50W - I say this because two of the same speakers were used in the 100W amp, the Twin Reverb II. The baffle board (front panel where the speaker goes) is 20mm ply and the speaker hole is 270mm diameter. It's held in place by eight screws with 11/32" nuts. (9mm does ok but it's not quite right). If you fit a speaker of less than 22W power handling you can expect it to blow eventually, with a real chance of taking some part of the amp with it. (In fact some folks say, a valve/tube amp needs a speaker rating of twice the amp's RMS rating. This is what Fender did for this amp.) It's often said that one Fender amp you can use a different impedance up or down by a factor of two without damage (in this case, 4 to 16 ohms) which opens up wide possibilities in using other speakers or cabs. In extreme-volume situations a higher impedance than the amp-maker's stated value of 8 ohms will stress the primary winding of the OT, and a lower impedance will stress the secondary. That can get expensive. If you get a different diameter speaker... it won't fit in the hole! Duh! ......However this still leaves you with plenty of choice if you want to replace the speaker.

The original speaker (Eminence version) weighs about 3Kg (about 6.6lb). Almost any  replacement speaker will weigh more, except the neodymium types.  

Different speaker models come with varying numbers of mounting holes. After removing the original speaker you may have to remove some of the original mounting pegs. Don't break them off! They will unscrew - this is done from the FRONT of the speaker baffle - remove the grille (see the dismantling page) to get at the cross-heads, and remember they're reverse thread, so turn them clockwise to get them out. (That's the wood-thread which is reverse thread. The nut-thread is normal.)

The Original Speaker
The standard-model factory-fitted speaker was Fender part number 019465. In the early days it was made by Pyle and had a smaller magnet assembly. That part number didn't' change when Fender changed to Eminence. I don't think there's much difference in the sound, and it definitely makes no difference to the value of the amp. Two of these were used in the 100W Twin Reverb II, so I assume they're rated at 50W. The Eminence weighs about 3Kg (6.6lb). There's a range of amp serial numbers running from F309xxx to F312xxx (includes part of 1983 and part of 1984) where it could be a Pyle or an Eminence. Maybe there was a time when they had Ps and Es on the shelf, all mixed up. And I already know the serial numbers weren't issued consecutively. Maybe both kinds of randomness were in operation at the same time.

                      Pyle normal-issue speaker from start of production                                                                                                                                                                        Eminence normal-issue speaker from 1983 onward.
                                photo - Greg G (thanks!)                                                                                                                                                                                                                 photo - me. I've done some dusting since.

The Original Upgrade Speaker
The PRII was offered with an Electro-Voice speaker as a factory-fitted option, called model 12F. (The same Fender part number speaker was used as the EV upgrade in the London Reverb, which is rated at 100W, so I assume that's the rating for the speaker!). I don't know how much more it cost or weighed. I was pleased to hear from Greg in Texas. He bought his PRII, with the EV option, new in 1982. He had the chance temporarily to change his speaker for the Pyle or Eminence, and  reports that the EV is much, much louder. The thought scares me because I think the PRII is plenty loud with the stock speaker. The EV looks like this;

(photo -  thanks to Bob Herrmann)

Big magnet, eh? I wonder what effect that has on the sound. Viewed from the front, this speaker has an aluminium central dome - under normal lighting it's visible through the grille cloth - which makes me think it produces piercing highs. One contributor below says it was great for clean work. He replaced his with a Celestion Greenback, which has a more bluesy reputation. But I haven't heard either.

Paul Rivera (the man who specified the amp) said of the EV speaker "The issue there was more about getting the cone moving. Those EVMs have very stiff cones and spiders. At low level, they were the coldest, least inspiring loudspeaker you ever heard, but turn them up and they were magical." That's from this interview.

Replacement Options
A different speaker will make your amp sound different. There are trade-offs to capitalise on, or beware of. You could choose another speaker purely on efficiency, and end up with a speaker which is far louder but sounds dreadful. Speakers also introduce their own type of distortion when pushed hard; it's a different kind of distortion to that introduced by the electronics, and has a distinct character of its own which we may or may not like. It's called 'cone break-up'; it's the opposite of the hi-fi ideal of the speaker behaving as a 'perfect piston'. You could fit a speaker which has a far higher power rating; it will last forever and will never add any of its own distortion (which will be a plus or a minus depending on your taste). Or you could fit a speaker with no spare power handling capacity, so the amp can push it into cone break-up more easily.

Then there's which material the cone's made from, the magnet type (ferro, alnico, ceramic), the magnet size, the material of the centre cap, the presence or absence of varnish on the edge of the cone (doping)... the options just go on and on. Alnico magnets 'compress' the dynamic range - as you turn up the volume, it eventually reaches a point where it doesn't get any louder, just distorts more (but in a nice way). Ferro magnets do this least, with ceramics in between.

(The original speakers, all types, are rear-loaded - see photos above - they're bolted to the back of the baffle-board. Some speaker cabs are front-loaded, ie, you bring the speaker to the cab from the front and it makes contact with the front of the baffle-board. I believe that's preferred if the speaker is very heavy or the baffle-board is weak. Plus it moves the speaker about 25mm forward compared to rear-loading, so if you've got a very deep speaker.... anyway, I can't imagine anyone wanting to do this on a PRII but if you do, then you have to read the new speaker's specification sheet carefully for the required hole-dimension and baffle-board thickness. The existing baffle-board hole is 270mm diameter, and the board is 20mm thick. The rest of this page assumes rear-loading.)

If everything else appears equal, check how many screw holes there are around the rim of the speakers you're considering  buying. The original has eight, evenly spaced around the circle. If your new one has six, you'll have to spend an extra hour removing two screws and precisely re-positioning four others. Celestions need four, I believe, so that would simply mean removing the other four.

With some other amps, you can't fit some speakers (even with the correct cone size) because the magnet is too big and hits some part of the chassis. Considering how big the magnet is on the EV speaker factory option, magnet-size probably isn't an issue on the PRII, but please let me know if you run into such a problem. Also - a tech on the FDP described this - with a non-standard speaker,  it is possible, on some amps, for  the new magnet to be too big / too powerful / too close to one of the valves/tubes; you can fit the speaker in, but the magnet bends the electron beam inside the valve, thus reducing the signal! I mention this for interest; I don't think it's going to happen on a PRII.

Browse through the discussion pages linked from the  PRII home  page and you'll see folks raving principally over Webers, Jensens, Tone Tubbys, WGS,  and Celestions. Older Jensens seem to be regarded as the classic Fender-tone speaker. Weber are applying modern techniques and huge amount of know-how to offer a wide range of different-sounding speakers. Jensen are no longer made by the original owner of the Jensen name or by 'vintage' methods; they do 3 relevant ranges,  C12K, C12N and a C12P; all made in Italy; all seem to have their fans. Celestion, apparently, sound British (surprised?), which means they're probably useful for playing the bad guys in American films. One guy I'm in touch with has a Scumback speaker. Who thinks up these names? I'd be pleased to hear from you if you've used any of the above, or others I haven't heard of.

Some new speakers need to be 'broken in' - that is, the flexible parts are stiff when new and don't sound very good for the first 2 or 3 hours of use. After that time they become louder with a fuller tone. This was true of my new Jensen. Some people 'break in' the speaker before fitting - they connect it to a radio and leave it playing for a couple of days. Others say that doesn't help, and it only 'breaks in' when used for the purpose you bought it  for, so just play loud and be patient. If you're anything like me, you need the practice anyway.

Changing the Speaker

I worked all this out for myself, and so could you, but hey, it only took me half an hour to write up.

You need a new speaker, a cross-head screwdriver and a 9mm or 11/32" spanner. (As I said above, 9mm isn't quite right but it does. 11/32" spanner is exactly right.) Maybe a wood drill, maybe some new speaker connecting tags.

Warning; the speaker screws have very sharp pointed ends (why?). They are like 8 spikes waiting to hurt your hands and damage the speaker cone.

Switch off the amp, unplug it from the wall, pull the speaker jack out of the back panel.

Gently pull the speaker lead off the tags.

After removing the chassis, you need  the spanner to loosen the eight nuts HALF WAY ONLY on the eight speaker screws. (Normal thread; loosen anticlockwise). A ring spanner might not fit around the nut (mine did - just) because of the shape of the speaker metalwork (the 'basket'). A socket won't work unless it's a very long socket, because the screws are long and the socket won't sit down far enought to reach the nut. Once the nuts are loose you can use a socket, with no handle, to unscrew them HALF THE LENGTH of the screws.

Now check the speaker pulls away from the baffle-board. It it's sticking, it may need some gentle prising away. Once you're sure it's detached from the baffle-board, you can safely remove all the nuts, hold the speaker really firmly, and lift it clean out of the cabinet. Don't drop it onto the screws (they will damage the cone).

My new Jensen C12N Reissue has eight mounting holes and went into the cabinet with no changes to the screws. Because of this, the whole job took less than an hour. (If you need to remove or re-position screws, this is done from the front of the baffle board with a cross-head screwdriver. You've already removed the speaker grille as part of the dismantling process. The thread which holds the screw in the wood is reverse thread so they come out clockwise. Remove the unneccessary screws and/or drill new holes in the baffle board as necessary.)

Think about which way 'up' the speaker should be - in my case there are eight steps around the circle; eight ways the speaker could go in. The obvious thing is to rotate it so the label reads the 'right way up' but the real question  is, will the speaker lead reach from the tags to the speaker socket? Also it's important that the speaker lead doesn't lie close to any of the parts that will get hot, so it's best to turn the speaker so the tags point to the 'input' side of the amp.

So choose which way 'up' the speaker will go, place it carefully over the screws (again, avoiding cone damage), place and  tighten the nuts, but not as tight as if you were working on a car; you don't want to distort the shape of the speaker metalwork.  (Tightening is normal thread; clockwise. Engineers will want to tighten one screw, then the one opposite, then another, then the one opposite, etc etc. Non-engineers will never understand why that's important to engineers, and shouldn't worry about it). Connect the speaker lead to the speaker (the Jensen uses the same size tags as the original). Put the chassis back. Replace the upper rear panel. Reconnect all leads. Job done! Now play it hard for a couple of hours to 'break it in', and finally email me with what kind of speaker it is and the difference it's made.