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Old March 8th, 2012, 08:55 PM   #1 (permalink)
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Oxford Speaker construction comparison UPDATE

Hi folks,

Recently I posted detailed information about constuction details of the voice coil and magnet structure of a 1962 Oxford 10K- series speaker...with the promise that I would dissect a 1970's era 10 inch Oxford.

This was in an attempt to add some real engineering data to the "late model VC gaps are bigger" controversy that has plagued the Oxford speaker for some years on the internet.

The 1974 dissection is now complete. Here's what I found:

First, to refresh your memory, here are the numbers for the 1962 model speaker. These were taken from an OEM coned 10K5 Oxford, Late 1962 construction, OEM in a 1963 Concert. (This speaker is a "chocolate and champagne Oxford, often revered as the "best sounding" Oxford.)

Voice coil: 1.25 nominal
Slug diameter: 1.244"
Ring diameter: 1.333"
Coil gap: .089"
Loaded Coil gap spacing: .0173"
Coil former .00825 lacquered paper former
Coil Wire: 39.2' of 34 gauge (.00625) red enameled copper wire
Nominal DC resistance 7.3 ohms (measured using a recently calibrated RCA WV-98 VTVM)
Coil wind density - 6 winds per mm
Coil layers - 2
Coil running width - .490" (10.3mm)*
Coil wind direction - (two layers) wind proceeds clockwise and front to back to front, when viewed from the front (cone side) of the coil.
Coil polarity - positive marked lead is the right-hand wire. It enters the coil stack and winds clockwise when viewed from the cone side.
Slug (magnetic) polarity - cone side face of slug is magnetic North

(*remeasured using a more accurate measuring fixture since the first data set was published. This number was confirmed twice, and measured side by side with the 1974 model)

Now, BELOW are the numbers for the 1974 Oxford speaker. All measurements below were taken with the same tools and methods. All 1962 numbers were retaken and reconfirmed at the time of the 1974 measurements. The 1974 parts were compared side by side with the 1962 VC assembly and hard parts.

Speaker: Oxford 10L5-1 (Black framed - blue decal "Fender Special Design" - typical in 70's Princetons, etc.
S/N 465-440 (40th week of 1974)

Voice coil: 1.25 nominal
Slug diameter: 1.245"
Ring diameter: 1.330"
Coil gap: .085"
Loaded Coil gap spacing: .0169"
Coil former .00829 lacquered paper former
Coil Wire: 39.4' of 34 gauge (.00625) red enameled copper wire
Nominal DC resistance 6.8 ohms (measured using the same recently calibrated RCA WV-98 VTVM)
Coil wind density - 6 winds per mm
Coil layers - 2
Coil running width - .496" (10.5mm)*
Coil wind direction - (two layers) wind proceeds clockwise and front to back to front, when viewed from the front (cone side) of the coil.
Coil polarity - positive marked lead is the right-hand wire. It enters the coil stack and winds clockwise when viewed from the cone side.
Slug (magnetic) polarity - cone side face of slug is magnetic North

(*remeasured using a more accurate measuring fixture - confirmed twice, and side by side with the 1962 model)

The above list for the 1974 model is not a "copying accident". These are the actual numbers - amazingly identical to the 1962 model, I'd say.

Here are some direct comparisons of the voice coil gap (the supposed "loose gap" era)

62 VC gap - .089
74 VC gap - .085

The 1974 unit's VC is actually smaller not larger, by .004 as compared to the 1962 unit.

VC thickness

62 VC - .0145 (wire) .0195 including former
74 VC - .015 (wire) .02 including former

The 1974 VC is actually .0005 THICKER than the 1962 - so the VC gap is actually tighter than the 62 model, albeit by a tiny and probably mechanically irrelevant amount.

The coil protrusion (depth that the voice coil runs in the magnetic gap) is as follows:

1962 Oxford - .640
1974 Oxford - .640

Yes, Batman, that's identical.


Conclusion. The 1962 Oxford 10K5 and the 1974 Oxford 10L5 are functionally identical in all respects related to voice coil structure. The one and ONLY difference between the two speakers is the mass of the magnet structure. The 1974 Oxford has a visibly larger magnet structure than the 1962. (I am currently unable to perform magnetic flux density and precise weight measurements. That's next - as soon as I acquire the necessary equipment.)


Let the flames begin!

:-)

Cheers,

CBG

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Old March 9th, 2012, 12:01 AM   #2 (permalink)
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No flames, are these ceramic magnet speakers or Alnico we are talking about?
I have a pair of 12 inch Oxford Alnicos marked 12k5R-13 465-438 that sound great.
Not sure what they came in originally. Sorry, I cant dissect these for you.
I have had a couple older Oxfords in Champs that sounded excellent but most sounded pretty flabby.
Rob
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Old March 9th, 2012, 12:03 AM   #3 (permalink)
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ROFL... I thought this was going to be a thread about the grammatical differences between British and American spoken English.
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Old March 9th, 2012, 12:16 AM   #4 (permalink)
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interesting, though it is still possible the early, VS late voice coil gap only applies to 12" speakers, this is still invaluable information
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Old March 9th, 2012, 01:48 AM   #5 (permalink)
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Robster- these are ceramic magnet Oxfords. 10K5 and 10L5

Caferacer, Yes, 12's may be different. Also, it is possible that early 60's and mid 70's Oxfords were built to the same spec, and that there was perhaps a period in the late 60's where Oxford tried something different - realized it didn't work, and went back to the old recipe.

I'm searching for a 1967-1970 Oxford now.

Cheers,

CBG
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Old March 9th, 2012, 01:53 AM   #6 (permalink)
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All I can say so far is that 1962 and 1974 Oxford 10's are mechanically identical with only a difference in magnet mass. I can't speak for any years in between.

If folks hear someone claiming that 74 Oxford 10's sound bad "because they have bigger voice coil gaps" please tell them they are mistaken about the voice coil specs. They are functionally identical to the 1962 specification, and I have the hard data to prove it.

I'm tempted to give 3:1 odds that the 1967-1970 Oxford 10 voice coil specifications are also identical...but we'll see when the numbers come in. Until then...

Cheers,

CBG
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Old March 9th, 2012, 02:20 AM   #7 (permalink)
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Brilliant analysis CoolBlueGlow! It is great to see real data on these Oxfords. It has never added up that Oxfords are terrible speakers when they were so successful within the recording industry.
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Old March 9th, 2012, 02:21 AM   #8 (permalink)
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Great info CBG. I've always liked the Oxfords. I find them warm and rich sounding.

I never noticed any big difference in sound between the 60's and 70's era. I like the early

breakup.
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Old March 9th, 2012, 09:59 AM   #9 (permalink)
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Hi Vibrosonic,

Yep - I think your ears must be spot on... because there is NO physical reason I can find that a 62 champagne/brown "uber" Oxford would would sound vastly different than a garden variety black frame blue decal "Fender Special Design". They are mechanically identical.

I would think (this is an OPINION) that the later models might go a bit louder before breakup, since they have a larger magnet assembly...but that might not be true. The larger magnets could easily have been a cost cutting and/or marketing effort (as in cheaper/lower flux magnet + looks bigger but same Oersteds in the flux gap = great sales tool at the Speaker Convention!)

I'm starting to scrounge for 12L's now.

I'm just guessing on this one, but I think this "Oxfords have bigger VC gaps" legend might well end up in the same discard pile as the one about "metal tubes are microphonic"


Cheers,

CBG
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Old March 9th, 2012, 10:03 AM   #10 (permalink)
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Haha... I laughed and laughed when I read this.

Funny how what we write means so many different things.

Quote:
Originally Posted by Hoopermazing View Post
ROFL... I thought this was going to be a thread about the grammatical differences between British and American spoken English.
The U.K. and the U.S.A. are two nations divided by a common language.

:-)

CBG
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Old March 9th, 2012, 04:53 PM   #11 (permalink)
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........................way to go!

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Old March 9th, 2012, 06:20 PM   #12 (permalink)
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CBG, that is interesting stuff there. I am going to think that if you were to analyze the higher wattage OXfords that were used in the 6L6 amps, you would find the differences that have been mentioned. I am going to think that there is where FEnder was having trouble with the narrow gaps OXfords not holding up to the punishment of a 40-85 watt amp....12T6 and 12L6 speakers. BAck in those days, noone was taking a PRinceton or Deluxe out to gigs. Those were 'student' amps at that time. S, noone was 'pushing' those little amps hard enought o cause any problems, I would think.
I for one do not doubt that there are narrow gap OXfords. I had a '67 BF PRo REverb with orignal Oxfords in it that was an anemic amp....no volume much at all until I put EMi Gb128's in it. Granted the GB128 is a 102db speaker, but the volume of that PRo REverb more than doubled. I also have had a sFTR with OEM OXford 12T6's in it that would yield some nice power tube action without causing earbleed. I am therefore keeping a pair of '68 12T6's that I have had for years just for the purpose of taming another TR in the future. IT is not a myth that Oxford changed their speakers to decrease the warranty problems, imho. I have heard 6g amps that ran 6L6's and Oxfords that had much different output than later FEnder 6L6 amps with the 'narrow gap' OXfords.
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Old March 9th, 2012, 07:12 PM   #13 (permalink)
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Cool Blue Glow, I have a late 60's 12T6 that came from a Twin. I'll have to check the code for the exact year.
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Old March 9th, 2012, 07:29 PM   #14 (permalink)
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Hi Wally,
Yes, I understand what you are saying. There may well be fire behind all the smoke against the 12 inch Oxford series.

I certainly don't want to in any way cast doubt upon Weber's work in the vintage speaker industry, nor do I question your experience or the experiences of many others like you who repeatedly report that they've found SOMETHING wrong with the tone of the 12 inch Oxfords.

Anyway, I'm looking forward to completing the analysis of the 10" line (filling in the gap with a late 60's speaker.) If I find that the gap was constant for 1962, 1967ish and 1974, I'm going to pretty much conclude that the idea of a wider gap 10" Oxford is a myth.

Then I'll start looking for 12" Oxford examples to dissect. That should be very interesting!

Bill - Thanks! Are you offering this Oxford to me as a dissectible example? If so, I can dissect it and return it to you afterwards (as a frame only, of course).

Oh, p.s. OFF THREAD, but Wally - what cathode bypass caps do you use in a AA764 Vibro Champ. As you probably recall, stock RC is 1k5/25/25 on V1A and 1k5/10/25 on V1b.

Today, I substituted in some 2.2uF in both places. Sounds o.k. but maybe lost a little too much bottom end? Appreciate any thoughts you (or anyone else has on that)

Cheers,

CBG
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Old March 28th, 2012, 08:11 PM   #15 (permalink)
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Hi,CoolBlueGlow.In one of your posts regarding dissecting an Oxford you mentioned a 10K-6.
Did you misspeak?All your other posts I've read mention a 10K-5..
If it was a 10K-6 I'd really like to see a pic of the model code.
I have never seen a 10K-6 although some literature and the internet lists them as OEM on Brownface Vibroverbs.
I have seen a few stock Brownface Vibroverbs and they all had 10k-5's in them.The only info you ever find on a 10K-6 seems to be coming from often quoted Fender Amp Field Guide.
Greg Gagliano in his articles about speakers says Vibroverbs came equipped with 10K-5s.
I'd really like to know once and for all if anyone has ever actually seen the mythical 10K-6.
Thanks,L
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Old March 28th, 2012, 09:11 PM   #16 (permalink)
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Quote:
Originally Posted by CoolBlueGlow View Post
ROFL... I thought this was going to be a thread about the grammatical differences between British and American spoken English.

Haha... I laughed and laughed when I read this. Funny how what we write means so many different things. The U.K. and the U.S.A. are two nations divided by a common language. :-) CBG
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Old March 28th, 2012, 11:20 PM   #17 (permalink)
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I just purchased a pair of 1964 Oxford alnico 12L6N-23's and they're coming this week. I believe the seller stated they came stock in his '64 Bandmaster cabinet. My "new" '64 Vibrolux 1x12 came without a speaker and these are the exact model and date codes. This picture came from the seller;

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Old April 2nd, 2012, 10:08 PM   #18 (permalink)
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Very interesting stuff here! I've always been a big fan of (most) Oxford speakers that I have owned. Tonight, I've been comparing tones from some 12T6 and 12L6 speakers I just acquired. One confirmation first though please; My experience tells me that Oxford started applying little white rectangular stickers (instead of their previous ink stamps on the frame) around '67 or '68. Is that what you folks have also concluded? OK, back to speaker tone. I played a "red plug" 12T6-10B 465-019. 19th week of 1970. It sounded nice and balanced, as well as efficient. I then played a 12T6-9 465-814 Fender blue label, 14th week of 1968, and it was strikingly less efficient and had no top end. Any thoughts, similar experiences, etc? I didn't even know "red plugs" were made as late as 1970. Nor do I know what the red plug was for, and how it's construction differs from other 12T6? I have several 12L6 here to try in the coming days (some from 1964 and some from 1968)
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Old April 2nd, 2012, 10:28 PM   #19 (permalink)
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A friend of mine bought a SF Pro Reverb, came with ceramic Oxfarts. It was an early 70s model. It sounded lame, dull high end and not very loud. We replaced with Oxfarts with Webers and it made a huge improvement. The Webers were mo'-betta in all regards. Louder, more lows, more but smooth highs. Don't know specifically why this pair of Oxfarts sounded so lame. If you like 'em, more power to ya.
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Old April 2nd, 2012, 11:15 PM   #20 (permalink)
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BJ, I'm just interested in Cool Blues analysis, and wondering if there is something to the hypothetical question of whether Oxford played around with some stuff designs (in the late 60's perhaps) that didn't work out very well causing them to go back to tried and proven recipes from the early/mid 60's. So, a question, is there a chance your friends SF Pro Reverb was a 68, 69 or 70 model, as opposed to early 70's?
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