Cordovox CL30 Rotary Speaker - Update and Follow-Up Question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mabinogeon, Jun 9, 2019.

  1. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    The second project I picked up today is a '60s Cordovox CL30 rotary speaker cab.

    From what I gather, this is the same as a Leslie 16 and the Fender Vibratone. (It's made by CBS, and there's a Leslie sticker on the inside with oiling instructions):

    A few pics:

    I'd like to add a grounded plug, but would like to ask for some advice on how to accomplish that. Please see the last pic for a close-up. There are a number of wires coming off the switch, and no power transformer - so I am assuming it's a bit different than adding a grounded plug to an amp.

    I wasn't being careful and got a pretty good shock when testing... but it works!
     
    Last edited: Jun 25, 2019
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  2. Baxtercat

    Baxtercat Member

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    Dang, that's cool.
     
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  3. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    Thanks! It belonged to a good friend of mine who bought it new in the '60s (he's twice my age). He played accordian in several local acts, and also has the huge, heavy Cordovox amp that goes with this.

    It's been in his basement since the late '80s, so he told me to get it out of there and put it to good use.
     
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  4. teleman1

    teleman1 Supporting Member

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  5. teleman1

    teleman1 Supporting Member

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    Wonder if the covering on the back of the speaker is asbestos??
     
  6. Baxtercat

    Baxtercat Member

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    Likely Fibreglas batting, like in old Bassman cabs?
     
  7. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    Thanks for that! I ordered some proper Hammond oil, just to be safe.
     
  8. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    It's a weird sort of layered blanket. Doesn't look like any fiberglass or asbestos that I've ever seen:
     
    Last edited: Jun 11, 2019
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  9. billyguitar

    billyguitar Member

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    I think it's a paper product. I'm really sure it's not asbestos.
     
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  10. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    Could be. It has sort of a cottony/fabricy feel. I'd peel it off to check further, but am afraid there may be a million spiders or something inside... :eek:
     
  11. xtian

    xtian Member

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    Schematic available?

    If not, hey, just connect Earth to chassis. If you don't pop a breaker when you flip it on, you're good to go!
     
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  12. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    Thanks for the reminder, I got wrapped up in a different project... Here's the schematic for the Cordovox:

    This is actually a schematic from a Leslie 16, but I'm nearly certain they're essentially the same unit.
    C5 and C6 in the schematic are .1uF, whereas in the Cordovox they're .22uf
    C3 in the schematic is 200mf, but in the Cordovox it's 70uf.

    Perhaps the difference is in application - as the Cordovox was made for an electric accordian and not a guitar? I can replace them if the consensus is that that's a good idea (been looking for an excuse to buy some Jupiter Yellow caps anyway).

    As for the grounded plug: I have added several to old amps - black to fuse to switch, white to transformer, green to chassis. But this beast is a bit different in layout, so I want to make sure I do it properly... Also the switch has six terminals - five of which have something soldered to them.

    As you can (hopefully) see in the pics, there are four wires coming off the far side of the fuse holder and the mains black wire is connected to two terminals on the switch (one direct and one through the death cap (C4). The two black wires coming from the transformer go to the fuse holder and to the same switch terminal as C4, which I assume is a death cap. I am accustomed to the switch coming after the fuse on the same wire - this thing having the switch on one wire and the fuse on the other is throwing me off and I'm having a hard time visualizing the correct way to do this! I'm assuming C4 has to come out of there, but then I don't know if I need to run a mains wire to both switch terminals. Drawing a blank.

    I should also add that this model doesn't have the typical Leslie crossover - it has a TRS plug that plugs into an amp's extension speaker jack.

    Thanks for your assistance, and please let me know if you'd like a different picture or some better info. I don't think I described that well.
     
    Last edited: Jun 12, 2019
  13. xtian

    xtian Member

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    The schematic shows everything floating WRT the chassis. In reality, is ANYTHING connected to the chassis?

    Second important question: I assume this has an input jack somewhere, right? Where is it? Most critically, where does the ground terminal of the input jack connect?

    In short, to prevent death by misadventure, we want the input jack ground connected to the chassis, and the Earth conductor of the power cord connected to chassis also.
     
  14. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    There is one resistor that ties together two terminals on the power switch and is then connected to a terminal strip at the grounded lug, along with the black wire from the hardwired footswitch:

    Not really, no. It has a TRS plug at the end of a 20' cable that is then hardwired inside the chassis. But I imagine one could replace that with a jack if one wanted:
    It's hard to see in the pic, but the ground wire from the cable is soldered to the same lug as the black wire, which then runs to pin1 of S1 on the schematic.

    If I follow what you're saying, I can simply move the ground wire from that cable to the next lug over, which is unused and riveted to the chassis and then add my 3-prong power cord, leaving the black and white wires in the same configuration they're currently in and bolting the earth conductor to the chassis? Seems too easy... And in that situation, I assume capacitor C4 would remain where it is?

    Thanks again!
     
  15. xtian

    xtian Member

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    Let's stop to consider. I'm getting the picture that the guitar (via that input three-conductor cable) and the speaker are isolated from the rest of the circuit. Also, that the entire Cordovox circuit, AC and motor are isolated from the chassis, and that neither AC hot or neutral wires ever come in contact with the chassis, the speaker, nor the guitar's input cable.

    If this is all true, then the whole Cordovox thing is similar to a vacuum cleaner, where you cannot touch any metal parts, so it simply doesn't matter whether a 2-prong power cord is plugged in any which way.

    In this case, there's no point in adding a three-conductor power cord and earthing the chassis.
     
  16. pdf64

    pdf64 Member

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    Presumably the chassis is user accessible, eg to plug in the footswitch? If so the chassis metalwork must be grounded.
    I don’t see any need to connect the speaker input sleeve to the chassis ground though; better maybe to let that and the rest of the circuitry float.
    I’m unsure though, perhaps the transformer secondary and footswitch metalwork should be ground referenced.
     
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  17. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    There is a small area of exposed chassis on the bottom where the power switch is mounted, so you could potentially touch the chassis every time you flip the switch.

    That makes sense, and is what I initially thought myself. But something gave me a zap through my guitar strings when we tested this. Granted, that was in his basement in I don't remember what vintage amp - it certainly wasn't a newer one, however. So perhaps the issue wasn't with the Cordovox after all?

    I ordered a bottle of Hammond oil, so I won't put this thing back together until I have a chance to lube all the moving parts. Once I do, I'll poke around with my multimeter to see if the chassis is hot. The power cord is in rough shape, so I'll have to replace it one way or the other.

    Another thought just struck me, but I won't have time to think about it until after my kiddos go to bed tonight - Why does it have a TRS plug when it plugs into a mono speaker jack? I get the T and the S, but what's the R for in this situation? Perhaps related to the footswitch, as they share connections on the terminal strip? I realize that may be a dumb question, but I am still new at this - my apologies. I wish I had a manual for this thing - It's made to go with a Cordovox CAG-1 tone generator and the manual may have some answers.

    Thanks again!
     
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  18. xtian

    xtian Member

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    You’re asking the right questions. Checking everything out with your multimeter.
     
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  19. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    Once again, I was over-thinking things...:oops:

    When I see a disc capacitor on one leg of the mains, I assume death cap. Not the case here - it's a snubber cap. So it's back to easy-peasy - new cord, black to fuse, white to switch, green to chassis.

    The Leslie oil came today, so I'll get everything buttoned up in the morning and gas it up.

    I'm still thinking it wouldn't be a bad idea to replace the caps that are in there, just because of their age. That can wait though, I want to get this thing running!
     
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  20. mabinogeon

    mabinogeon A really hoopy frood. Silver Supporting Member

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    Update: Up and running and it works like a charm! And I have a life-time supply of Leslie oil if anyone needs some.

    Follow-up question: The next issue I've run into is actually running this thing safely - I tested it with the extension jack of my 5E3 clone, but due to impedance issue, I don't want to run it for any length of time.

    Every amp I have has an 8ohm OT, an 8ohm speaker, and a parallel-wired extension speaker jack. The Cordovox speaker is 4ohm, so if I run them together I end up with a 2.67ohm total load, which I understand is a bit too far off the mark to safely operate for an extended period without damaging the OT of my amp.

    As far as I can tell, my options are either:

    put a new OT in the amp (which then means I can only use the Cordovox with that particular amp),
    build a separate amp head to use exclusively with the Cordovox,
    or put an 8ohm (combined load of 4ohm) or even 16ohm (combined load of 5.33ohm) speaker in the Cordovox (which I understand is "close enough" for a tube amp - so I could at least use it with any of my amps).

    Is there anything I'm missing? Putting a big resistor in series with the Cordovox speaker? Wiring a second small 4 or 8 ohm speaker in series inside the Cordovox cab?

    Thanks again!
     
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