The Workbench

JBL D120F Questions

1

Summary of Questions:

  1. What is your cone number ? I want to figure out what the original cone numbers were and if mine is original. (Mine is XHF-3685, where X is illegible)

  2. IF you have voice coil numbers please state them. (Mine is VL9400)

  3. Do you have paper surrounds ( One piece paper cone with integrated paper surrounds) or cloth surrounds for D120F or earlier models.

  4. If you ever disassembled an original D120F or earlier D120, was the coil former aluminum ?

  5. Do you know if aluminum wire was used as voicecoil and during which time periods ?

Background info.

For those of you that read and commented on my threads, would know that I am totally new to D120 speakers. The relevant thread explains the reason why I never adopted them.

I found a blown D120F that is quite easy to fix, but I am a bit baffled whether the cone and coil/former is authentic. I am finished repairing it and will reassemble, but before that, I have some questions. It is the one speaker I know almost zip of ... to my own detriment. I missed a LOT! In this case it really didnt help not being born in the USA.

1) The cone has the following number XHF-3685, where X is illegible.

2) The voice coil and former is a darn work of art. The former is aluminum, the coil wire is copper (could be enameled aluminum) and is deep-edge-wound

3) The Voice Coil assembly (motor) number is VL9400 Some claim that the D120's were issued with Aluminum coil wire. It seems odd, but hey, what do I know about JBL.

I need someone who has a D120F (in particular not the early 60s ones) to post their cone numbers. Although it would be great to have the cone numbers for the non F versions also and definately what kind of surrounds they had. All in one paper cone, integrated paper surround or separate cloth surround.

If anyone disassembled a vintage original D120 / D120F can you remember if the former was aluminum ?

An aluminum former is going to make a HUUUUGE difference to the higher frequency response. That I can promise you. The aluminum cap connects straight onto the aluminum former. That will create extreme presence. I cannot see that this effort and expense would be done by a recone supplier.

I dont have to recone at all, but the recone kits they sell these days, have phenolic type formers. In that case the D120 will sound more like an EV. why even bother. Buy an EV. I can see why no-one like these recones.

Furthermore the early 60s D120's had solid paper cones including the surrounds. It seems later models like the D120F has cloth surrounds. can anyone a fundi on JBL maybe confirm or debunk this statement ?

I would appreciate some info if you have, and apologize if I let you grab the screwdrivers and wrenches to check your speakers.

The more info the better.

Cone Number

Motor was offset a few degrees had to remove to reset it at 0-deg. Motor assembly Number

Needs new surrounds: Disassembled

2

As I recall, D series all had paper surrounds, and K series & later had Cambric (cloth) surrounds. Very few still have the original cones, and D series cones disappeared in the 70's. Cambric is high compliant and works well with solid-state amps. Paper surrounds work much better with tube guitar amps because they have almost no damping factor & like to have something to push against to prevent overshoot and help the amp control the cone. AFAIK, no aftermarket JBL cones have been very good.

3

Thanks Billy. You confirm a suspision I had. So the Cambric surrounds appeared much later mid 70's or anyone has some accurate date when they were introduced ? So your suggestion is that I should go at all cost for all paper cones with no cambric for tube amps ? Your suggestion sounds very plausible and makes a lot of sense. The cambric surrounds will possibly have a lot of Bass Flab with a tube sound. More for HiFi. Mine as in the photos has cambric. so far it seems I will have to get a new all paper cone and leave this cambric surrounds cone for another application.

If anyone compared cambric vs all paper please let me know what sound differences you found.

The remaining issue is the aluminum coil former vs the phenolic coil former. Which were used when and for what.? I am not sure if my aluminum former was maybe a JBL HiFi version ? Maybe cambric went with aluminum former for HiFi. It does makes sense, although the frame is an orange D120F !! pointing to maybe a later JBL recone to a HiFi conversion. It looks just too high quality for a recone supplier, so there my guess it is a factory hifi recone.

25

Fender painted them orange. That's what the F was for. The D120Fs were musical instrument speakers with a wider voice coil gap for more robustness and a doped surround so they wouldn't dry out when used outside, They were a tiny bit less efficient. D120s are Hifi speakers but can be used too. You should search 'Harvey Gearst' and if he's still around see if you can contact him. He was the fellow at JBL making all these speakers. His favourite for guitar is the D123 which is a hifi speaker. I have a couple in my amp builds and some D208s in a little stereo guitar amp I built. JBLs are glorious.

Oh and if it has the cloth surround it probably has a K120 cone kit in it. That's what was often done. It could be a JBL factory cone but just for the K series which was a higher powered instrument speaker.


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