why distortion and what is the cure

I'd have to agree with Edesilva's last comment, it sounds as if you have hit the output limits of your system. Many systems are at or near peak output at the 1-2 o'clock positions. And tube sound typically goes downhill very fast once you hit peak output.

I also agree with the under powered amp and clipping scenario. How old are these speakers? I couldn't even find this model listed in the Agon Bluebook. If they use '70's or early '80's drivers with foam surrounds (the outer edge of the speaker cones), you might check this material to see if it has deteriorated. I have seen foam surrounds actually turn to dust!

Tjz, I disagree regarding your statement about tube amps! Tube amps will gradually start to distort when overdriven (this can actually be beneficial, as guitar players use this method to generate a myriad of sounds and tones), while solid state amps usually start clipping almost immediately when overdriven...this is bad news for speakers!

You're right Fatparrot, a guitarist can use the distortion from a tube amp to create various sound effects, but that is in a totally different environment and setup than a home system. In fact, some guitar amps will include this "sound" to be added to the playback, depends which head you buy.

But in a home system setup, this sound would be very undesirable for playback. Fuzzy, static, breaks up, distorted, whatever you would like to call it. When a tube amp hits maximum output, the sound becomes undesirable for CD or LP playback.

In what garyatware@blueyonder.co.uk indicates, "When i turn up the amp past about 1 o'clock the sound just breaks up/distorts", his description indicates that his system is hitting maximum output.

The simple math: 87 dB speakers, 12 watts of power, your not going to get a lot of overall output in dB, maybe 90-93 dB, and then it will break up. It probably sounds good between 9-12 o'clock volume settings. And (keeping in mind that most systems vary) most systems will peak somewhere between that 1-to-3 o'clock setting on the volume knob (again, as described).

Now, I guess some of the troubleshooting questions I might ask is:

How old are the tubes? How many hours of run time are on them? Also, is the amp auto-biasing or does this need to be perfomed manually (I am not familiar with the setup and operation of a sugden). I might suspect that an older amp that has not been biased in sometime would require this, as well as old tubes. And especially if both are true, this would effect the sound quality, especially at higher outputs.

I might look into the amp and tube setup to ensure peak performance. Then I would check to make sure each tube is in good, operational state.

Thanks again, Todd

Thanks guys - yes i think the speakers are inefficient for the amp(thx edesilva) but am sending the amp to Sugdens for a service and they can test it.Fatparrot- The speakers were made as the front end for cinema setups and were manufactured in 2000.I naievly let the salesman talk me out of a pair of Mission for these and regretted it since. What speakers can anyone suggest for a 12 watt amp please? (bear in mind $600-700 second hand limit!!!) Sugdens suggest Totem arro, or snell ? Cant find Snell at all here and the totems are hard to come by.

I listened to some Totems last Thursday, they were quite lovely. I was surprised by how much bass the Rainmaker bookshelf speakers made. I also listened to the Arro and Forest. All very good sounding speakers. But, in regards to the Totems, they are not any more sensitive than what you currently have, most are around 87 dB, but the range is from 85-88 dB, and you are not going to get a lot of sound output with a 12 watt amp, no change from what you currently have actually. The sound characteristics may change, but the output (volume) won't.

Haven't heard the latest Snell speakers (though I loved their earlier generation speakers), but you are not going to gain any sensitivity with these either, they run 88-90 dB, again, not a significant difference.

Having the Sugdens serviced is a great idea, but I would look for a speaker that is more efficient than 87 dB, something at least 90 dB's, preferably more. This will make your setup a lot more efficient and cleaner sounding when turned up.