Conference napalm::guitar

      YES - but I should clarify that.
    
       Some heads have one 8 ohm jack and 1 four ohm jack. If there
    is one four ohm jack that usually means the manufacturer expects
    you to connect the second cab out of the first - but not all speaker
    cabs have two jacks. It would be easy to add one. Drill a hole and
    match the wires on the new jack (receptacles available thru music
    stores or radio shack) exactly to the existing jack. This will allow
    your speakers to run in parallel (two 8 ohmers in parallel is 4
    ohms).
       If there are two four ohm jacks (that's what mine have) then
    you can connect both 8 ohm cabs to both jacks or just one four ohm
    cab to just one jack. Usually I just plug one 8 ohm cab in the 8
    ohm jack. Keeping in mind that tube amps are impedance matched there
    is no real increase in wattage at lower ohmage (as in solid state
    amps) and impedance mismatches can cause a lot of trouble. 
    A "pre-fight" checklist isn't a bad idea before firing up any tube
    amp and can save you repair bills. (thanx- Steve_G)
    
    							-john r.
    

    
    Just get a M/B Mark III and don't worry about it blowing up!!!

    I can't believe I've been playing so long and don't know sh*t about
    this, but ya can't find out without askin'.....
    
    I built a 2 x 12 cab to use with my 100w Kitty Hawk M3 head.  I wired
    up two 12" speakers in a series (positive to positive, negative to
    negative, a set of wires to the jack from one of the speakers).  I
    measured the resistance with an ohm meter at the end of the speaker
    chord that goes into the amp, the other end plugged into the cab.
    The resistance was about 9.5 ohms.  Does this mean I have an 8 ohm cab
    and should be using the 8 ohm output from my amp?  I *think* the
    speakers are 4 ohm, but they're not marked.
    
    P.S. when I say I built a cab, it actually means I stood there and
    handed Pat Blair the tools, fresh beer etc.  What a guy!
    
    Steve

    
    Positive to positive and negative to negative is *parallel* wiring.
    
    Series would be jack pos. to speaker #1 pos., speaker #1 neg. to
    speaker #2 pos., speaker #2 neg. to jack neg.
    
    What kind of speakers?  Lotsa 16 ohm Celestions out there.  Sounds like
    8 ohms to me.
    
    							Brian
    

Steve's using some old Peavy Scorpians that I had laying around.  I mean these
babies are 'old' !  I think they must be eight ohm.

jc

	I suspect that you are confusing IMPEDANCE with RESISTANCE.

	DC resistance is very easy to check. Most 8 ohm speakers are
	between 4 and 6 ohms when measured this way. This is a static
	check.

	Impedance is measured based on the frequency of the voltage
	being applied (ie. Reactance), and will be different for
	any frequency that you apply. Most speaker impeadances are
	measured at 1000 hz. At that frequency, the speaker will be at
	8 ohms.

	To connect in series:


		   + +----+ -    + +----+ -
	+ o----------|    |--------|    |------------o -
		    /      \      /      \

		Impedance = ohms + ohms

		ie 8 ohms + 8 ohms = 16 ohms



	To connect in Parallel:

	+ o------o------------------o
                 |                  |
                 |                  |
		 |  + +----+ -      |  + +----+ -
	         +----|    |----+   +----|    |------+
		     /      \   |       /      \     |
                                |                    |
                                |                    |
		                o--------------------o------o -

		Impedance = ohms / # of speakers (assuming the same
						  impedance for each
						  speaker)

		ie: 8 ohms per speaker / 2 speakers = 4 ohms



	The colored dot on the speaker indicates the + terminal.

	If you use jacks, the center tap is +. The outside case
	is -.


								Jens

    What the heck is this hookup....it's the one I used:
    
             + ------   + ------------- +         cord
             speaker one    speaker two   jack ---------- =  9.5 ohms
             - ------   - ------------- -
                         
     this is what resulted in the 9.5 ohms at the end of the
     speaker cord.
    
    Steve D.

    re: .7
    
    That looks like parallel to me....
    
    guy

	It's parallel. Probably uses 16 ohm speakers also. You can't
	measure impeadance with an ohm meter, so I can't be sure.
	
	Worst case, you are running 4 ohms. Can your amplifier handle
	this??. Probably, as 4 ohms is a common configuration for
	cabinets with 2 speakers in them, however, if you add another
	cabinet with this same configuration & it's also in parallel
	you will bring down the load to 2 ohms & it's unlikely that this
	will good for your amplifier in the long term. 4, 8 or 16 ohms
	are common impedances for speaker cabinets. You can take 2  4
	ohm cabinets & wire them in series & get 8 ohms, or 2  16 ohm
	cabinets and wire in parallel & get 8 ohms.

	Try to stay in the range 4 thru 16 ohms as you load & the amplifier
	should be ok. I find that wiring cabinets in series makes it
	safer to connect other cabinets up, simpley because you can
	connect the other cabinet in parallel.

	Cross over networks don't follow the same rules, for example:

			    c1		 + ---/
	  + o--------o------||-------------|   Midrange / Highs
		     |              +------|
		     |		    |	 - ---\
		     |              |
		     |		    |          /
		     |      h1      |    + ---/
		     +-----(((()-----------|   Woofer
				    o------|
			            |    - ---\
	  - o-----------------------+          \


		NOTE: the - speaker terminals connect together.

	c1 is a capacitor (for example 10 uf at 100 volts)
	h1 is a choke (for example 9 millihenrys)
	Off the top of my head, I think that this crossover is about 2000 HZ,
	based on  the values shown. Use a 'BIG' choke if you expect
	to handle in excess of 100 watts.

	Because this changes the frequency reponse of the load, the
	impedance tracks at roughly 8 ohms (if both speakers are 8 ohm
	speakers).

	You can add a PIEZO tweeter across the the terminals on the
	midrange/highs speaker to get the extreamly high frequencies.

	Piezo's impedance changes with frequency also. At low frequencies,
	they are thousands of ohms. As the frequency increases, thier
	impedance drops.

								Jens

    Steve, got any friend who are HW techs?  They should be able to measure
    the impedence of the cabinet for you so you're sure.
    
    Hate to see you blow up a new Kitty Hawk (after you finally get it
    working).
    
    Greg

    Possibly too late, I ran the KH in the 8 ohm jack for one hour at
    practice last night, it's now dead.......
    
    Sh*t....

	Don't feel too bad, I bought a Phase Linear 400 watt sterio power
	amp & found that if one channel is not connected to anything (ie.
	no load on the left or right side) that it very shortly destroys
	the output stage on that channel (8 power transistors), which in
	turn causes a power suppy imbalence on the other channel. The
	end result was 140 V dc applied directly to what used to be speaker
	voice coils in my P.A. system. The 50 cent fuses in the output stage
	were saved by the destruction of my 15 in speakers and all 16
	output transistors (I guess that's what they mean by 'fuse protected').

	The speakers have been re-coned & the power amp sits under my 
	workbench, as I ponder my own design for a new output stage.

	In all cases, 8 ohm loads are the safest & 16 ohm are the next best
	choice. My Twin Reverb runs it's 2 12's in parallel at 4 ohms.
	I guess KH's don't like 4 ohms.

								Jens

    Oh no!  Should have used someone elses cabinet if you weren't sure... 
    
    Greg

    
    	Re .12
    
    	Jens, sorry to hear about the amp disaster. I've had the same
    	experience and learned the hard way
    
    	Phase Linear amps used to be advertized as "$1 per watt"
    	and you get what you pay for. PL amps have only thermal pro-
    	tection. They're a very basic power amp, but sound very good.
    	I've used the 400 and 700 for sound reinforcement a looooong
    	time ago and found that they;
    
    		A) Can't handle less than 8 ohm loads
    		B) Fry the output devices with no load
    		C) Oscillate with no input applied, creating
    	   	   the loudest air raid siren howl I ever heard
    		D) Overheat and shut down easily due to inadequate
    	   	   heat sinks
    		   
    	Pro Audio companies used them because they were cheap, but not
    	without modifications. They were originally designed for the
    	audiofile who intended to put it in his stereo cabinet, hook it
    	up, and leave it.
    
    	Neal-who-still-fears-Phase-Linear
    
    	

    After several discussions and tests, I was pretty sure I had an 8 ohm
    cab.  I have heard that it was safest to use the 8 ohm output anyway. 
    I demoed Coop's KH head on Sunday when we finished building the cab and
    it ran fine for over half an hour.  I don't know what happened, but the
    KH is going back to LPMG.
    
    Steve

	re. Greg House....

	Can I borrow your speaker cabinet for my next test???

							Jens

    Oh funny guy!  ;^)
    
    ...at least I know what impedence it is (you should too, since you gave
    me instructions for wiring it...)
    
    Greg