Fender Bassman 10 Speaker replacement

[Jake]

Hi,
I am looking to replace my 1972 Fender Bassman 10 speakers. Should I
try and find the original speakers, and if so what kind are the
originals? Basically, I want to be as close to the original as
possible. Any recommendations would be greatly appreciated!

Thanks,
Jake

[Paul Angle]

Hi Jake
   I would look into a re-cone.  There is a good place in SoCal.
Paul

--
You received this message because you are subscribed to "The Amp Guide" group.

Thank you for your support.
www.ampwares.com
www.mojotone.com
www.guitarandampshow.com

[mi...@nycap.rr.com]

Jake,

Here is a place to start for some info: http://www.ampwares.com/amp.asp?id=30

Mike

[B L]

Hi Jake,

72 Bassman 10 is most likely CTS (Chicago Telephone Supply) Mfg. code (stamped in ink on the speaker frame would be 137 if CTS. 

Here are other possible codes.

Oxford code is 465

Utah is 328

Eminence 67

Jensen 220

Ampwares suggests that JBL speakers were an option as well. Personally, I've never seen a JBL equipped Bassman 10.

Except for one unique feature, the CTS 10 is a fairly generic 10" ceramic magnet 1" or 1.25" voice coil paper cone stamped steel frame loudspeaker. It features a conventional paper bobbin overhung voice coil using enamel insulated copper wire of about 29-31 gauge. The paper itself features stiffening grooves to improve low frequency response and decrease distortion. 

That one most unique and difficult to match aspect of your 4x10 Bassman OEM speakers? That will be the fact that these are 32 ohm speakers (!) The are wired in parallel, for a combined DCR of 8 ohms. 

Fortunately, if you want exact CTS replacements, you can find these from several places. 

1. Fender PA columns from the era - they also used 32 ohm CTS speakers and should be identical to what is in your Bassman. Look on eBay. You can find them - sometimes...and the price is often quite right because "they're 32 ohm" (e.g. most people think they're worthless.)

2. Fender Rhodes cabinets (pricier, but also sometimes carrying the CTS 10" 32 ohm speakers)

Another non-CTS option for 32 Ohm would be Mod10/50 Jensens. They are fairly similar to your CTS in many respects, if you want to buy new.

Another choice would be these Kustom speaker columns. Here's an example on ebay right now

 http://cgi.ebay.com/2-VINTAGE-KUSTOM-4-X-10-SPEAKER-COLUMNS-/370396865723?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item563d5fa4bb#ht_1763wt_1139

These three appear to be Oxfords or perhaps CTS. You could inquire the DCR from the seller. 32 ohm units will be obvious. the DCR (DC resistance) should be well over 20 ohms... easily distinguished from 4, 8, and 16 ohm units. Of course, you'd need four of them...

If you can't find 32 ohm speakers, all is not lost. You can replace the CTS speakers with four (4) eight ohm units from a variety of manufacturers. You must, however, wire 8 ohm speakers in "series-parallel" to achieve the requisite 8 ohm load your amp requires. Again, very easy - to see how to do it, simply look at a wiring diagram for any Marshall mono 4x12 cabinet from the 1960's or 70's. They are wired series-parallel. Wire your four (4) eight ohm replacement speakers exactly the same way. 

With new Jensens, one choice I would look at would be Mod 10/35, which come in 8/16 ohm. Get the 8 ohm and wire them series parallel.

Another less obvious but potentially interesting option would be something like this: (if you could find four of them)

http://cgi.ebay.com/VINTAGE-10-ZENITH-ALNICO-WOOFER-ROLA-2-VC-N-I-C-E-/390198417797?cmd=ViewItem&pt=Vintage_Electronics_R2&hash=item5ad9a35985#ht_746wt_913

This is a Zenith unit - with a 2 inch voice coil and Alnico magnet. You might have to look a while to find four, but they are out there and would probably work fine.

Finally, DO NOT get big magnet low efficiency speakers. You want low wattage units - a rating of 20 watts per speaker is more than enough. Be specific - for new speakers, ask the db output for 1 watt input at 1 meter. anything less than about 87 is not going to cut it. 

Good luck with your Amp. I love the Bassman 10. A great and much under-appreciated classic Fender design that is actually quite true to what most people consider "classic" blackface design than other more glamorous amps of the era such as the Silver face twin, etc.

Cheers!

Keith

[Jake Glascock]

Keith,

Thanks for the detailed info! It has really helped to clarify alot of things.

 

A couple of questions: you mentioned both the MOD 10/50 Jensens and the 10/35 (32 vs 8 ohm).

 

Wouldn't it be easier to just get the 10/50s and rewire it the same as what is already in the amp (assuming the speakers in the amp are wired series parallel)? Is there that much of a difference between the two types? I am just curious if one can really tell the difference as I have never compaired the two speakers.

 

Anyways, thanks again for you advice.

 

Jake 

[B L]

Hi Jake,

Second question first: why not "keep the same wiring" You could. it merely limits your speaker choice to the Mod 10/50 32 ohm unit. Tone wise, 32/4 = 8, vs. 8x2+8x2/2 = 8.  With either wiring configuration and the appropriate impedance, the amp sees the same load, so that matters not. If you want to use 8 ohm speakers to save weight, money, or change speaker tone, the amp doesn't care...as long as you wire them to an 8 ohm total load.

Why Mod 35 vs. Mod 50?

Simple - The Mod 10/50 is rated at 50 watts. the Mod 35 is rated at 35 watts. Since either speaker in a 4x10 configuration is plenty capable of handling the power of your Bassman 10, I'd lean towards the 10/35 simply because they are lighter and cheaper. both are about equally efficient. However, after further investigation I see from reviewing these speakers at Jensen that the are voiced "more English" which translates to "like a Celestion". They show a resonant frequency peak of 107 Hz, vs. a peak of 97 Hz for the Alnico 10/25 and 96 for the Vintage Ceramic 10/25. That makes them better for guitar, and not so better for bass. They may also "flap out on you" on the low notes.

So in order, best to worst match, compared to the TONE of your CTS OEM speakers, I'd say 

1. Jensen Vintage Ceramic C10R or C10Q
2. Jensen Vintage Alnico P10Q or P10R
3. Jensen Mod 10/50
4. Jensen Mod 10/35

In order of cost, least to most, its;

1. Mod 10/35 x 4 = about 160 bucks street
2. Vintage Ceramic C10R or C10Q x 4 = about 170 - 190 bucks street
3. Vintage Alnico  P10R or P10Q x 4 = about 375 - 400 street
4. Mod 10/100 x 4 = about 425 street

Note that with the Neodymium (Neo) series. You would gain 3db output, 3.5 pounds of amplifier weight, and loose from $50-165 additional bucks out of your wallet compared to your other choices. They'd probably sound a bit cleaner and tighter, though...and they'd have those sexy neo magnet structures. Very hip.

So, I guess I'm modifying my original recommendation slightly towards the vintage ceramic C10R or C10Q.

If you play really loud, get the Q, the little extra voice coil beef will help your durability. If you are playing at modest volumes, or want a little breakup in your tone, go with the R. 

Finally, if you wire them series/parallel, understand that if you blow any one speaker, you will loose it's "mate". Keep an eye out for that. Your current setup, they can blow one by one, and unless you're paying attention you may not notice when the first one goes.

Cheers!

[B L]

Jake, 

Oh, and one more thing...If you wire the speakers yourself, pay VERY close attention to the proper phasing, especially as you do the series parallel wiring. It is very easy to get wrong. Just be careful when you wire, follow the Marshall schematic closely, and make sure that you clearly mark the "+" terminal on each speaker AND on each wire in your harness, so you know which is which.

After you hook up the speakers, set your volume to a modest level and just "thump" your bass while you carefully observe the direction of motion for the cones of all the speakers. All cones should move the same direction. If you can't tell by looking, play a low note. You'll know if you have it wrong when you play a low note. If your tone sounds seriously bass deficient, nasal, or otherwise "off", you likely have one or more speakers out of phase.

If you search online, you'll find some folks who recommend using a battery to phase the speakers...because it is a DC source with a defined + and - output. Personally, I avoid using a battery to "phase" my speakers. The amount of current delivered by a battery can be fairly substantial, and voice coil wire is pretty small. IMO, there's no sense in taking a chance with your expensive new speakers, when thumping can reveal the same thing. Others my feel differently about this...just my preference. I've done it in a pinch, and I've never blown a speaker, but it is not my preferred choice.

Finally, I always check the phase by watching and listening, even when I've visually seen that the wires appear to be properly phased. Just by way of example, I have a pair of original coned JBL D-123's right now who's phase is inverted to each other when wired according to the terminal colors!