NEW SPEAKER FOR AMPEG J12R: HOW MANY WATTS?

After replacing the tubes in my small 1997 Ampeg J12R, a15W single channel amp, I'd like to change the poor stock speaker ( rated at 25W) that breaks up quite early and farts when deep bass notes are played with humbuckers or powerful P90s.
I'm still wondering which is the best choice for a 15 Watts amp , a 35Watts or a 50Watts rated speaker....
This amp has very little room for the speaker in the cabinet because there's a metal protection for the tubes mounted right in front of the magnet, so the speaker must not be deeper than 121 mm. The majority of speakers ( particularly alnico speakers) don't fit , and then I'd like to buy something here in Italy , to avoid expensive shipping and Customs duties. As everybody knows ,nowadays Jensen speakers are made in Italy and seem to be pretty good too.
After some web researching I 've decided to try a ceramic Jensen CH 12-50 ( this same model is named MOD 12-50 for the USA market).
I read some reviews and many report that the 50 watts rated version is somehow warmer and more balanced than the 35 Watts.....so I'd like to try that one, is that too powerful to be driven correctly and with a nice powerful tone by a 15 watts amp?? Is the 35 Watts model more appropriate to the low wattage of the amp??
I'd like to have good clean sounds and tones also at high volumes , and then for distorted tones I've got my pedals so perhaps the 50 watts could be a fine choice ...
Well, as you can see I'm a bit confused about it..
please if someone can help .....

My recommendation would be a Celestion G12H - it's rated at 30 Watts but can take more, comfortably, is LOUD (100dB efficiency - typical new Jensens are not nearly as efficient), sounds great in single 12 applications, and is one of those rare Celestions that sounds great in an open-back combo. Works as well for clean sounds as for overdriven tones, and shouldn't be silly expensive or hard to get in Europe.
The high efficiency rating of the speaker will give a twin EL84 or twin 6V6 amp enough headroom to play with a drummer comfortably.

What Walter said; speakers with more power handling have bigger, thicker parts; magnet, voice coil cross-section and maybe diameter, and a stiffer cone. The 50W might sound warmer but it's more likely to be found in an amp with higher output ... not an amp like yours. The 50W speaker is rated at three times your amp's power output; at some point, that speaker is going to become less responsive.

Thanks for your answers Walter and John.
I agree that of course Celestions are generally totally superior speakers to current production Jensens.
I read specs and reviews about the G12H model and it surely seems to be the perfect replacement, it's a bit more than twice the price of the Jensen CH12-35 ( this would be now my alternative choice to the Celestion now as from what you both confirmed I understand that a 30-35 rated speaker is definitely the best solution for a 15 Watts amp) and probably worth the difference, but what worries me is , as I already wrote in my other post, the dimensions :the Celestion G12H is 135mm deep, while the Jensen CH12-35 is 107mm deep. The stock Ampeg speaker I want to replace is 121 mm deep, and it's just 30 mm ( = 3 cm) far from the metal tube protector that is mounted in front of the power tubes. Installing the Celestion I'd have a distance even shorter ( only 15mm= 1,50 cm) from the magnet to the protection...is that safe or would cause strong vibrations and noises of the tubes ??

I 'd buy the speaker on line ,because it's too difficult and more expensive to find a good selection and those models in stores , so I 'm not in the condition to check how it works in that cabinet with that tube protector so close...
Maybe that short 1,50 distance is enough and I'm getting paranoid about it?

mmm..another thing I just noticed looking at the specs diagrams is that the Celestion G12H has 4 mounting slots ,while my stock Ampeg speaker has 8 slots ( and so the Jensen CH12-35)..is it possible to install the Celestion speaker correctly in a cabinet with 8 slots ? Is it just a matter of tightening the 4 screws very strongly or it just doesn't have to be made?

Can't you just get rid of the "tube cage"? Is the 1.5cm the distance from the cage, or the actual tubes? I think you should be just fine without it.

Four mounting screws for a speaker is perfectly OK, no problem. And never overtighten the mounting screws on a cast-frame speaker - that's the way to warp your cone and maybe even dislocate your voice coil!

Thanks for your encouragement Walter..
I attach a photo of the back of the amp to show how things are: I could get rid of the metal protection, but that was factory added to protect the tubes from very strong vibrations causing noises ,being so close to the magnet..Ampeg decided this "improvement" after lots of complaints from the previous series owners that lamented the tubes were exposed to excessive vibrations and rattled a lot. I'd like to keep the tubes protected, the base of the metal protection is covered with thick rubber , the tubes are less prone to vibrations that way...
The actual distance from the magnet to the external side of the protection is now 30mm ( 3 cm) , a little bit more from magnet to the tubes as you can see from the pic. Installing the Celestion G12H would reduce the distance from magnet to protection to 15mm ( 1,50 cm) ..

I'm glad to hear from you that also a 4 slots speaker can replace a standard 8 slots Speaker with no problems in leaving the other 4 holes and slots unfilled..
I'd like to invest in the Celestion, as I really love this little amp and want it to play at its best, since I bought it last May I used it for 90% of my gigs ( even with those issues that I already planned to solve) after 15 years of using my old Fender Hot Rod Deluxe.., but I 'd like to be sure it fits the cabinet ....

Hmmm....That's a tough one, I don't really know if that could have any negative effects. Not the smartest design decision by Ampeg if you ask me - maybe somebody there has calculated how much money they'd save by making the cabinets less deep...

Is the speaker mounted in the middle of the baffle? If it isn't (if it's mounted to one side) you could perhaps try flipping the baffle 180 degrees to get the magnet further away from the output tubes? (if the baffle is in any kind of way removable and not glued into the cabinet, that is....)

Walter Broes said:

... Is the speaker mounted in the middle of the baffle?..

Click to expand...

Hi Walter; not the best pic but the speaker looks to be mounted in the center ... reference the handle above. If it isn't dead center, flipping the baffle will only move the center of the speaker just a little:




You can gain clearance by replace the cage with wire tube retaining clips like These.....

.....maybe. If the tube sockets are bolted in, no problem. Take the bolts out, put the clips in, and replace the bolts. If the sockets are riveted in, then you'd have to drill out the rivets, put the clips in, and replace with fresh bolts. Drilling out the rivets will spray metal bits around the chassis ... extra care has to be taken to brush / vacuum / shake all the little pieces out.

If the tube sockets are done with bolts, this is easy; if riveted, it becomes a lot of work just to gain a few centimeters / millimeters / fractions of an inch of clearance. If you amp is new or under warranty ... this might jeopardize the warranty. Wish I had a better answer. John

Thanks again guys.

I'd like to avoid doing any modification to the cabinet, drilling holes and so on..I just want to find a good speaker that fits there.
The wire retaining clips are a smart idea abut I'm afraid it won't solve my problem: the actual problem for installing the Celestion isn't the presence of that cage ( because even if deeper it wouldn't touch the cage) ..is the extremely short distance of the TUBES to the magnet, even if I remove the cage ( and install or not the clips) the tubes are always there, and with a speaker deeper than the original one( like the Celestion) they're even closer to the magnet. Getting rid of the cage and installing the clips won't make that distance longer, it would solve the problem if the cage was a big one, stealing lots of room inside the cabinet and the Celestion would touch the cage....but what worries me is whether or not a magnet that close would make the tubes rattle or not, now at a distance of 3 cm they don't rattle , I wonder what could happen at a 1,5 cm distance (of course keeping the cage or even installing the clips to protect the tubes somehow).
I'm afraid the only answer is taking the risk of mounting that Celestion, or making a compromise to buy a good average speaker ( like the Jensen) less deep and surely fitting, rather than an excellent top-quality one like the Celestion...

Hi Andy: pic below is speaker bell and two 6V6s; the distance between the bell and the tube on the right (it was a little closer than the other) is about 1/2" ... I don't know what that is in centimeters ... it was fine for casual play. I don't know if there is a minimum distance. I also don't know for sure that there is more vibration near the speaker than there is further away but I can understand your apprehension about buying a speaker that won't work or one that makes you worry all the time ... that's no good no matter how good it sounds.

I wanted an alnico in mine but had to settle for a ceramic. I can't even remember what I put in there. Sold long ago......