Vintage Jensen C15N Speaker with an Alnico Magnet?
 

Doesn't the "C" on a vintage Jensen C15N Speaker frame indicate that it's a ceramic magnet and not an alnico magnet?

If you look at the picture, the label says it's an alnico magnet, but stamped on the frame is C15N which indicates it's ceramic.

Is the frame stamp correct or is the label transplanted from another speaker? I'm not expert enough to determine which kind of magnet it is by appearance, although I know alnico magnets that are used on speakers are smaller in diameter than a ceramic magnet.

The date code suggests it's was made in the 14 week of 1962. The seller said it was pulled form a B-15N.

No the "C" does not stand for ceramic. As an example the old alnico 12" guitar speakers were the P12 series. Coincidence only the C12Ns were ceramic.

The shape of the magnet and magnetic structure, and the stamp both indicate a ceramic magnet. Either version can produce great tones. The thermal power limit and Xmax are both very low by todays standards. An excellent driver for low power tube amps (35w or less).

Being that its ceramic, then the label from the factory was incorrect or someone placed the Alnico label on it at a later time, which IMO, would be highly unlikely.

You can not "tell" by the shape of the magnet. IIRC JBL "D" series were alnico, "K" were ceramic. Altec 421 and 418 were alnico. They just moved away from button style magnets to ring.

According to the Jensen speaker code info that I have been able to find, the "C" from C15N stamped on the frame respresents ceramic and the "P" from P15N is alnico.

Can anyone else shed any light on this? Beans-on-Toast, JohnK, Jimmi M?

1) Is the magnet ceramic or alnico?
2) If ceramic why does it have an alnico label on it?
3) Would this version have actually come out of an early
B-15N?
4) Date code indicates week 14 of 1962. Could it be 1952?

1. Just did some googling...the C15N's are ceramic. Why they say alnico 5, I don't know, but the statute of limitations to sue ran out long ago ;)

2. Don't know.

3. Absolutely. C15N's and P15N's were the original speakers used till Ampeg switched to CTS, though upgrade speakers were usually JBL D130F's.

4. Nope...no B-15's or EIA codes in 1952 that I know of.

An earliest Ampeg B15 amps would have had an alnico Jensen P15N speaker in them. It had a smaller diameter but taller magnet than the one in your image. They switched to the ceramic C15N not long after the amp was introduced.

The Jensen Concert speaker is consistent with what Ampeg was using in the B-15N in 63 perhaps 62 as well. My 63 B-15N has a ceramic Jensen Concert EM1500 which is essentially a C15N. The one in the image below is what the ceramic one looked like. With the cover over the magnet removed, it looks like a typical ceramic speaker. Very different than the one in your image.

I've seen speakers like yours before with the Alnico label on, so this one is not unique. They had the three screws on the back holding on the back plate like old alnico speakers had. That makes me think that it is an alnico speaker rather than a labelling mistake.

The Jensen Concert is a great sounding speaker and highly sought after in the Fender community for guitar amps. It also sounds great in my '63 B15N.

Jensen Concert ceramic EM1500.

not to get pedantic on you, B-String, but both the D's and K's were alnico and the E's were ceramic ;)

That's okay, I only fallowed JBL with passing interest, I was an Altec guy :)

The shape of the magnet and magnetic structure can reliably be used to distinguish between alnico and ceramic/ferrite magnets. Those having a flat, large diameter magnetic structure and magnet (disc-like) are ceramic. The C15N is a good example.

Some larger magnetic structures with an alnico magnet have a somewhat similar structure (magnet sandwiched between metal plates), but the magnet is thick rather than wide (cylindrical rather than disc-like). Those with smaller alnico magnets usually had a thick metal plate bent into a box-like structure.

The JBL D and K series drivers employed a cylindrical ring alnico magnet nested in a cast and precision machined magnetic structure. The magnet cannot be seen. These are among the most efficient magnetic structures ever produced, focussing nearly all of the magnetic flux into the gap. There is almost no stray field.

A further check is to examine the magnet for chips. The chipped surface of a ceramic/ferrite magnet will have a conchoidal shape and a chalky texture, and will appear non-metallic. A chip in an alnico magnet will be rough (Alnico is coarsely crystalline) and will have a shiny, metallic appearance.

heard a local blues bassist using an old GK400RB with an Altec (421B IIRC) loaded Karlson Coupler cab, pure tonal bliss :cool:

sorry for the derail, OP :hiding:

This was common then, I have a C15N of the same vintage that is labeled "Alnico 5" - they're really ceramic. The P15's were Alnico and they have a different shaped magnet structure.

Ampeg started to use the EM1500 in mid '63 around the same time as the first circuit revision (NA). '62's were all C15N's. In '61 they used both the C15N and P15N. Most of the amps from June '61 on had C15N's, but prior to that they used both. There doesn't seem to be any rhyme or reason as to why they were using both at that time period - it could've been an availability thing.

The speaker the OP is asking about was mine. It sold on Ebay today (it will be in the mail tomorrow).

A few years back I pieced together a B15 combo using an orphaned '65 head and '62 cab that I had found independent of each other. I did the simple mods that Jess Oliver was suggesting to get more volume out of a vintage B15, including a solid state rectifier and a four ohm speaker.

It was great having somewhat of a beater type B15 that I was not afraid to take out for rehearsals and small gigs - but I ended up selling it after a couple of years in favor of a PF500/115Ex2 combo when it was introduced. I regret this now as the PF rig has since moved on - but anyway, this cab is where the C15N in this discussion came from. I had sold the B15N combo with the 4 ohm speaker installed. I never doubted the C15N's originality to the '62 Ampeg cab, as the speaker's date code and the cabinets serial number reflected the same time period.

I have had that speaker hanging on a wall in my storage room for quite some time and I had never noticed the Alnico label until it was posted by someone else on the internet. Pretty funny

Well if it came from you, I'm sure the buyer will be happy.

Ha! Thanks.

Well I installed it in my '61 before listing it and it still sounds great. Now I just need to pack it well enough for any potential careless couriers it may come across:hmm:

Umm!
 

In that case the 418 was a stepped alnico magnet and the 421 was a ceramic magnet variant.

I bought the speaker in question. Nice to know who the seller is and the history. It'll go in my '63 B15N that came with a "newer" JBL E140-8. I want to get it close to period correct.

To bad we couldn't have made the the deal through talkbass, could have saved a little on e bay fees.

Looking forward to getting it.
Thanks