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Are my 1968 Fender CTS’s healthy?

Discussion in 'Amp Tech Center' started by fleshnbones, Nov 25, 2020.

  1. fleshnbones

    fleshnbones TDPRI Member

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    I bought a way cool 4x10 cab off a guy a few weeks back and one of the speakers was out. I opened it up and started working on the speaker that was out. I messed around with it a bit and finally got a resistance reading off of it at arpund 22ohms. I initially thought that was an odd reading and I really didn’t have the time or desire to take the other speakers out and read individual readings so I just threw the one back in and called it a day. Anyway, these are wired in parallel and I get a total resistance of 4 ohms. Sounds good to me. Is it? They sound great by the way but can anyone on here shed some light on how fender wired their stuff back then and if this was a common arrangement for a 4x10 cab. Thanks a lot. Now here’s some eye candy... FE0C3E0F-B2B2-466D-85DE-3872EDF826F8.jpeg 4035A489-B712-439C-9C2F-1683946CB8B7.jpeg AB3AF686-AC90-430E-A8A1-C857A23842E5.jpeg
     
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  2. Fretting out

    Fretting out Poster Extraordinaire

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    Cool!

    Is that one of those cabs that came with fenders solid state amps? Or Is it a P.A cab?

    Don’t think I’ve seen one, I know I’ve seen some funny looking cabs from the late 60’s from their solid state failure
     
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  3. Jon Snell

    Jon Snell Tele-Holic

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    I think they were produced around the same era as the WEM Pa series and is for Public Adress, mainly used in halls and the like as a fixed system.
    The impedance was around 7.5 Ohms as they were 30 Ohms each. (That has little to do with the DC resistance but was in the day of multiples of 7.5Ω. 3.75, 7.5, 15 and 30Ω). WEM used 3 x 12" 15 Ohm speakers in parallel ending up with around 5 Ohms to suite the PA100 solid state amplifier employing 2N3055 output transistors with a supply voltage of 95 volts as they had a Vceo of 120volts allowing for overshoot, so the speakers matched the amplifier for current and drive.
    Absolutely awful things.
     
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  4. Wally

    Wally Telefied Ad Free Member

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    please excuse my confusion here, but I have to ask a question or two.

    What is meant by “the speaker that was out”. Was this speaker not functional? Was it simply not connected to the speaker circuit?
    What did you do to ‘mess around with it a bit’? Could you not get a reading before you ‘messed around with it’ and finally got a reading of 22 ohms? Did you check to see if this speaker was a productive speaker before wiring it back in? Did you check the readings for the other speakers individually?

    Here is something similar to what you have there.
    https://reverb.com/item/904522-fender-spk-0410-1968-black
    These speakers were 32 ohm speakers wired in parallel for an 8 ohm load. However, some of those Fender PS (public address) amps called for a minimum load of 4 ohms while the PS160 called for a minimum load of 2.6 ohms. These numbers would be minimum numbers for two cabinets in parallel.
    But....I have no experience with these units. I would suggest opening the unit back up and doing a more detailed investigation...including making sure that each speaker is functional on its own. A 9 volt battery is useful for this as is a careful voice coil rub test.
     
  5. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Are your speakers healthy, you ask? If you pay the shipping, I’ll check them out for free. :):):)

    It may take a while; my tests are, um, exhaustive...
     
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  6. fleshnbones

    fleshnbones TDPRI Member

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    the speaker was wired in but was producing no sound. after taking it out i measured resistance but got nothing, open. so i looked closer and noticed that the solder on the terminals was old and dry so i resoldered it. voila, it worked and i got a reading of 22ohms. then i went over and ran the speaker full range through one of my audio amps and it did reproduce the music with no audible issues, so i threw it back into the cab, rewired and soldered and called it a day. the reason i didn’t check the other speakers for functionality is because I knew they worked.
     
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  7. fleshnbones

    fleshnbones TDPRI Member

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    hmmm...let me sleep on that one :lol:
     
  8. fleshnbones

    fleshnbones TDPRI Member

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    I had no idea what it was until Jon Snell replied to the thread. I had spent hours on google trying to find something similar and the only thing i could find was one that said ‘fender solid state’ on it but with different speakers inside
     
  9. fleshnbones

    fleshnbones TDPRI Member

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    Thank you for that cool bit of info. Interesting that this would be used as a PA speaker. Were the 10” alnico CTS’s used in any period tube amps?
     
  10. BobbyZ

    BobbyZ Doctor of Teleocity

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    Well yeah they kinda were.
    Most people really like them in Super Reverbs for one.
    The Fender amp ones were 8 ohms and don't have an aluminum dust covers. I don't know what your's are, but I have seen people selling non Fender labeled CTS alnicos out of God knows what, with aluminum dust covers. Of course they always want good money because of that Super Reverb connection.
     
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  11. fleshnbones

    fleshnbones TDPRI Member

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    Mine have a black dust cover on ‘em. I just got into electric guitar so I don’t know much about amps or cabs..it sure is a lot of fun to find out the history of the gear though. Thanks for the input
     
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  12. BobbyZ

    BobbyZ Doctor of Teleocity

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    Well I'm learning I need to keep my eye open for Fender PA speaker cabs!
    I've got a Super Reverb, well actually two, that now need major restoration, probably won't get to it anytime soon though.
    No idea what that cab set you back but those speakers, the Fender logo, handle and maybe some other things are worth something to someone. Actually the tolex on it is too, if it can be peeled off and there's enough to use.
    You can't buy correct blackface tolex today.
    They just sell the correct stuff for reissues.
     
  13. Wally

    Wally Telefied Ad Free Member

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    Thanks for that explanation. In your situation, I would be hesitant to run that cab with that speaker. 22 ohms is not a good reading for any speaker, ime. It would be of interest to know what the other speakers measure. 4 x 16 ohms in parallel would yield a 4 ohm cab, but the resistance measurement would likely be a bit lower than 4 ohms. Speaker load numbers are important, imho. Sometimes 9ne can take out an amp with an improper load. You don’t say what amp you used to run that check on this 22 ohm speaker, but if it was a tube amp, you put the amp’s OT in jeopardy. If it was a solid state amp, then there is no problem with a 22 ohm load; but had it been say a 2 ohm load and the amp had a minimum load of 4 or 8 ohms, that amp was in jeopardy. Since you are new to electric guitars and amps, you might want to exercise caution with unknowns.
    I would suggest a full analysis of all of the speakers. Again, 22 ohms is very odd....and ime incorrect.
     
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  14. Antoon

    Antoon Tele-Afflicted

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    I am not sure if these PA speakers are exactly the same as the speakers used in the Super Reverb (aside from the difference in impedance). I have read people saying that they sounded somewhat different than the guitar amp speakers.
    The speakers that for instance Jensen used to produced specifically for guitar use for (like the the fender P10R/Q's and Fender-C10Ns used in BF Fender amps, or the later LMI105 or EM1050s), almost always had very short voice coils, like 1/4" or even shorter, limiting their low end and low mid response and max cone excursion. Bass models of the same speaker often use taller coils. PA speakers may also use taller coils.
    That is the biggest problem I have with re-cones, almost always a much taller voice coil is fitted because short coils are hard to find nowadays. I have seen Weber re-cones with voice coils that were twice as tall as the original. This gives a completely different sound, more like a bass speaker.
     
    Last edited: Nov 26, 2020
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