[jman66]

Roger (or anyone else so inclinded to respond  ),

The RM-9 has three output taps, 2, 4 and 8 ohm.
Provided a speaker has basically a flat impedance of 4.5 ohms with no dips and only a peak into higher impedance, three potential hookups are possible:

A) Use the 2 ohm tap (any benefits from light loading the tubes?)
B) Use the 4 ohm tap (theoretically, full power should be available).
C) Use the 8 ohm tap (this tap has the most windings).

Based on the given load, can you extrapolate what the results may be when connecting to each of the taps?

[jman66]

- bump -

[Roger A. Modjeski]

Hi jman,

The answers are:

A.  Light loading is easy on the tubes and provides more damping, less distortion, less gain and less amplified noise from the preamp. It is also a way to limit the peak voltage to easily damaged speakers like the QUAD 57. As long as the system plays loud enough without clipping this is usually the best way to go. If you have speakers like Martin Logan's that dip to 1 ohm this should be tried.

B.  Matched loading, the 4.5 ohm speaker on the 4 ohm tap will give the full 100 watts.

C.  It is generally not a good idea to use a tap higher than the minimum impedance of the speaker. Most amps put out less power under these conditions and the missing power goes into the output tubes, overheating them and shortening their life. Distortion and damping suffer also.

The RM-200 and RM-9 SE (see rwalter's post for data on the RM-9 SE) are more tolerant of low impedances (below the tap value) and can actually put out more power into a load of half the tap. These designs came about because of a particular RM-9 owner had speakers that had a 3.5 ohm dip at 8 KHz. He was going through output way too fast and I asked him what he was playing. His answer: "Miles Davis and pretty loud". I mentioned that trumpets have very high energy at the frequency of the trumpet and went to work on a design that would solve that problem.

[jman66]

Thanks Roger - that answers my questions and was most informative!!