2. amps-preamps
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4 ohm vs 8 ohm taps

I just had my CJ MV75A1 tube amp rebuilt and the tech put on new binding posts and put the 4 ohm taps on them. I always thought 8 ohms was the most common but I dont know much about this subject. Two two sets of speakers I would use with the amp are either my Vandersteen 2CIs or my Klipsch La Scalas which with the new crossovers are 8 ohms . My other amps are all running the 8 ohm taps right now. I could use enlightening on this whole subject. Carl
solarcarl
stevecham
3,340 posts
 
Don't mean to hijack this thread in any way, only hope to augment it because I have a similar question. I have 2Ce Signatures and I see in the product literaure that the nominal impedance is 7 Ohms and the minimum is 4 Ohms. So what really makes sense from a rational standpoint which taps should I use? I'm hoping to hear something other than, "whichever sounds best." Thanks!
Steve
inpepinnovations1e75
395 posts
 
Stevecham, use the 4 ohm taps.
Atmasphere, further to my other note, the tubes don't 'see' the impedence on the speakers, but the impedence on the primary of the transformers, which DOES NOT change with the whichever taps one uses on the secondary.
Bob P.
eldartford
4,262 posts
 
inpepinnovations@aol.com...The primary impedance depends greatly on the secondary loading. If it didn't why would transformers have multiple taps?
inpepinnovations1e75
395 posts
 
Eldartford, you know of course that the secondary on the transformer has different taps, 4, 8 and 16 to match the speakers. Those taps simply have different amount of winding to 'transform' the primary winding impedance which is constant. The tubes themselves don't see the secondary taps or impedance.
Salut, Bob P.
eldartford
4,262 posts
 
inpepinnovations@aol.com...You have it backwards. The different taps of the transformer secondary make it possible for the tubes to see the same (high) impedance with different loads.

Here is a way for you to test your theory. Short out the speaker terminals of your amp and drive it hard. If your theory is correct, the tubes won't see the short. After the fire department has left, post results of this experiment :-)
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