[K.C.]

I was going through some stuff in my garage today and found a pair of Celestion SL600s I forgot I had. (Oops, too much gear.) Fortunately I had wrapped them in plastic and packed them well so they're in perfect shape.

I thought what the heck I'll take them in and check them out. I hooked them up to my RM-10 (8 ohm tap) and spent about an hour listening. They sounded great. I didn't hear any clipping but I noticed a high pitch sound after a while and I couldn't figure out where it was coming from. I stopped the CD and listened for a moment. I was surprised to find that it was the RM-10, apparently the transformers. I turned down the volume and it stopped.

Had I just pushed the amp too hard without realizing it ?

What would cause it to do this ?

The amp only has a few hundred hours on it and it's running the orginal RAM tubes. It sounds great. Too hot today to run my RM-9.

[Roger A. Modjeski]

This is unusual. If the sound went away when you turned down the preamp then the noise is coming in before the volume control which means the source or cables from the signal source.

[K.C.]

It happened again a few minutes later and did not stop when I turned down the volume. I stopped the input source and turned down the volume but it continued and changed frequency. I put one ear over the amp and it seemed to be coming from under the metal cover on the right side. Finally I turned off the amp.

The source is a Cal Audio CD > Benchmark USB DAC-1 and Audioquest viper interconnects. I've used them for some time with the RM-9 and never had a problem.

[K.C.]

Playing the same recordings and same front end components for the last hour with the RM-9. Sounds great, no oscillation.