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 Post subject: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 10:00 am 
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My first post. Any input is appreciated.

I've got a red knob dual showman head from what I presume to be the late 80's or 1990. It is paired with a Fender 4x12 cabinet which I believe was original to the amp and is referred to as "The Wedge" cabinet. As long as I've owned the amp, the impedance selector (which can be set at 4, 8, or 16 ohms) has been set at 8 ohms. Anyone have information on whether the cabinet really has an 8 ohm impedance? Also, does anyone know what kind of speakers were used in this cabinet? I've taken a speaker out and there are absolutely no markings on the back.

I'm considering building a 2x12 cabinet and I would like the ability to use it as an extension cabinet or on its own. Obviously, identifying the impedance of the original cabinet will influence how I build the new cabinet.

Thanks for any and all help!


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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 10:55 am 
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Buy yourself a ten-dollar DVM at Home Depot or Lowe's and find out.

IIRC, the OEM speakers back then were either Rola or Eminence. You may find some numbers stamped on the speaker frames. Make note of them and post the info here -- we'll try to sort it out and determine what you've got.

HTH

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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 11:56 am 
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+1

A voltmeter is really the only way to know if the speaker doesn't have markings on it. Your amp can easily handle a 1:2 or 2:1 mismatch, so whether the speaker is 4, 8, or 16 ohms having the amp's selector set on 8 is fine, but you're correct that you need to know the impedence for sure before adding an extension cab.

DC resistance and AC impedance are both measured in ohms but they aren't the same things. A DC voltmeter used to measure speaker impedence will give low readings -- that's normal and to be expected. A 4 ohm speaker will measure somewhere between 2 and 4 ohms (always at least a little below 4 ohms), an 8 ohm speaker will meter between 5 and 7 ohms, a 16 ohm speaker will measure between 12 and 15 ohms.

Once you measure the cab's total impedance, unplug one of the speakers and measure it by itself. Depending on the impedance of the individual speakers you may be able to rewire the 4x12 for a different impedance (if it's got 16 ohm speakers you can wire it for either 4 ohms total or 16 ohms total.)


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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 12:12 pm 
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strayedstrater wrote:
+1

A voltmeter is really the only way to know if the speaker doesn't have markings on it. Your amp can easily handle a 1:2 or 2:1 mismatch, so whether the speaker is 4, 8, or 16 ohms having the amp's selector set on 8 is fine, but you're correct that you need to know the impedence for sure before adding an extension cab.

DC resistance and AC impedance are both measured in ohms but they aren't the same things. A DC voltmeter used to measure speaker impedence will give low readings -- that's normal and to be expected. A 4 ohm speaker will measure somewhere between 2 and 4 ohms (always at least a little below 4 ohms), an 8 ohm speaker will meter between 5 and 7 ohms, a 16 ohm speaker will measure between 12 and 15 ohms.

Once you measure the cab's total impedance, unplug one of the speakers and measure it by itself. Depending on the impedance of the individual speakers you may be able to rewire the 4x12 for a different impedance (if it's got 16 ohm speakers you can wire it for either 4 ohms total or 16 ohms total.)


+1

I'd also like to see pics (if possible) of the "Wedge" cabinet.

Arjay

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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 12:32 pm 
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Very helpful, thank you both.

So - I took out the two bottom speakers and measured ohms. Lower right measured 5.3 ohms and lower left measured 5.6 ohms. I measured multiple times on all combinations of the 4 possible leads on each speaker. I kept measuring these numbers consistently. I believe the volmeter is a DC voltmeter (although it has a couple AC voltage options). Does this mean that the speakers are 8 ohm? I'm assuming that a 4x12 cabinet with 8 ohm speakers would be wired such that the total cabinet impedence would be 8 ohms. Perhaps each set of two wired in parrallel and then those two sets wired in series (or vice versa). I think that would add up to 8 ohms?? Without completely removing a speaker (which I don't want to do because the wire leads seem to be frozen to the speakers) I can't get my head in the cabinet to see the wiring.

Also, low and behold, there were numbers on the inside speaker flange. Each of the lower speakers had the following numbers: 026488 and 67-8723. Interestingly, there was another number printed on the backside of the cone which read 56T (I think).

Again, thanks for your assistance.


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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 1:05 pm 
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Eminence speakers, made in the 23rd week of 1987. The "026488" is Fender's in-house P/N for this driver, which itself may have been used in other models within the red-knob line.

You'll need to measure the impedance of the entire cabinet to determine how the speakers are wired.

Arjay

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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 1:21 pm 
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Image

This is a pic of the amp and cabinet...if I did it correctly?!

Thanks for the info on the speakers! Great stuff.

Any advice on how to measure the impedence of the entire cabinet. The only way to access the inside of the cabinet is through the speaker holes. Should this measurement take place on the wires near the cabinet jacks?


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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 1:59 pm 
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dshalfstack wrote:
Any advice on how to measure the impedence of the entire cabinet. The only way to access the inside of the cabinet is through the speaker holes. Should this measurement take place on the wires near the cabinet jacks?


Just disconnect the speaker cable from the back of the amp and put one lead of the DVM on the tip of the cable plug and the other on the barrel of the plug.

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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 2:06 pm 
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bluesky636 wrote:
Just disconnect the speaker cable from the back of the amp and put one lead of the DVM on the tip of the cable plug and the other on the barrel of the plug.


+1

"Elementary, my dear Watson."

:mrgreen:

Arjay

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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 2:30 pm 
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Before your replies, I took the cabinet jack plate off the back and measured the leads. Multimeter read 7.3 - 7.4 ohms. I then saw your replies (much simpler method) and got the same measurement. Soooo, looks like I have a speaker cab with an 8 ohm impedance.

To continue this line of questioning, if I were to build or purchase a 2x12 extension cab with an 8 ohm impedance how should I hook it up to my amp with the existing cabinet. See the attached pics.
Image

Image

Would I daisychain off the existing cab (not sure if thats the correct terminology)? If so would that be series or parrallel and what should the impedance selector be set to? Or should I use the main output for the 4x12 and use the series jack for the 2x12 - setting the impedance to 16 ohms or the parrallel jack and set the impedance switch to 4 ohms?


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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 3:14 pm 
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dshalfstack wrote:
Or should I use the main output for the 4x12 and use the series jack for the 2x12 - setting the impedance to 16 ohms or the parrallel jack and set the impedance switch to 4 ohms?


Yes.

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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 5:04 pm 
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Sorry for the silly question but I seriously do not know. What is the purpose of the two jacks on the back of the cabinet? Does it matter which one is used if it is the only cabinet hooked to the amp?

Also, what eminence speaker in their current lineup would come close to matching the tone of this cabinet?


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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 5:20 pm 
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dshalfstack wrote:
Sorry for the silly question but I seriously do not know. What is the purpose of the two jacks on the back of the cabinet? Does it matter which one is used if it is the only cabinet hooked to the amp?

Also, what eminence speaker in their current lineup would come close to matching the tone of this cabinet?


Without see the wiring inside the cab, I can only guess: Many multi-speaker cabs are wired so that if one output jack is used, the cab is wired in mono. Using both jacks splits the speakers into pairs measuring 1/2 the mono impedance each for stereo use. Another scenario may just have the speakers wired differently internally depending on which jack is used. You should connect the speaker cable to each jack, one at a time, and measure each one to see if there is a difference between the two.

Picking a matching speaker without hearing the original cab and the other speaker candidates would be impossible.

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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 5:50 pm 
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dshalfstack wrote:
Sorry for the silly question but I seriously do not know. What is the purpose of the two jacks on the back of the cabinet? Does it matter which one is used if it is the only cabinet hooked to the amp?

Also, what eminence speaker in their current lineup would come close to matching the tone of this cabinet?


Funny because Fender did this with all their heads. They are ALL external speakers where a head is concerned. But they saved money by using the same backplate as the combo amps. You need to have one cabinet plugged in the "Main Speaker" (center jack) and the other in either the Series or Parallel and set the Impedance switch accordingly.

Art


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 Post subject: Re: Red Knob Dual Showman "The Wedge" Cabinet
PostPosted: Sun Sep 30, 2012 6:55 pm 
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bluesky636 wrote:
dshalfstack wrote:
Sorry for the silly question but I seriously do not know. What is the purpose of the two jacks on the back of the cabinet? Does it matter which one is used if it is the only cabinet hooked to the amp?

Also, what eminence speaker in their current lineup would come close to matching the tone of this cabinet?


Without see the wiring inside the cab, I can only guess: Many multi-speaker cabs are wired so that if one output jack is used, the cab is wired in mono. Using both jacks splits the speakers into pairs measuring 1/2 the mono impedance each for stereo use. Another scenario may just have the speakers wired differently internally depending on which jack is used. You should connect the speaker cable to each jack, one at a time, and measure each one to see if there is a difference between the two.

Picking a matching speaker without hearing the original cab and the other speaker candidates would be impossible.


Thanks. I measured each jack seperately. Both measured 7.3 ohms. See the pic below. Looks like they are simply wired in series together. Any ideas?

Image

Also, concerning the speaker question, I understand that my existing speakers are Eminence speakers manufactured in 87. I had assumed that in the current lineup of Eminence speakers (speakers sold today) there would be one similar to these speakers as far as tonality.
Perhaps not, or perhaps I'm not asking the question clearly??


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