2. amps-preamps
  3. 1178450866

Have I damaged my amp?

Hi,
I have a Music Angel 300B amp which has been fine for sometime now. A friend visited to hear the new single driver speaker cabinets I've made, to compare these with my previous Kef's (the amp had been on for hours) I unplugged the Rt channel only and we had a listen for 30secs or so then I swapped back, the amp was still on. A few days later it started making loud rustling sounds 'under' the music (not volume dependent) on the right channel with some squeal when I tap the chassis, there is also quite a lot of noise when I power down from the Rt channel. I have tried swapping the valves with no change and have checked inside for loose connections 'bulging' capacitors etc and can see nothing wrong. So is this a probable cause for damage and what could it be? the problem is becoming noisier but only starts after the amp has warmed up an hour or more. My first thought is to replace the main capacitors under the transformer. I don't have a schematic for it but does anyone have any views on this.

Thanks,
Iain
irbow
irbow OP
4 posts
 
Thank's for the replies,

I turned the volume down and then swapped the speaker, I wasn't thinking. I'm currently using another amp because it's not enjoyable waiting for the noise to start, as I said I have tried swapping the valves one by one (with the amp off and cooled down ;) and the noise stays in the right channel which is why I'm puzzled (I wouldn't have posted if it had followed a valve). At switch off it's loud more tearing than rustling.

Iain
tarsando
578 posts
 
I don't think it's a good idea to run any amp without a load, but a tube amp with a transformer is more likely to endure it than an ss amp. That's always been my understanding of it. I know for sure that SHORTING the speaker leads blows an ss amp almost every time (unfortunately for me) but doing so with a tube amp doesn't seem to harm it. I could be wrong about the whole thing I guess....
jax2
3,031 posts
 
Hmmm, if you turned the volume all the way down and pulled the speaker connection, that in and of itself would not likely damage the amp since there's no signal to the amp. Still, not a good habit to foster. Had you shorted the connections on the disconnected wire you would likely have blown a fuse (assuming they are fuse-protected). Could you have crossed the terminations and shorted the amps? That's very easy to do with a speaker wire flopping around. Regardless, short of the tubes being bad, it seems like you should take the amp to someone who has the expertise to test out individual components within the circuit. I don't think damage will always necessarily be visually evident.
rwwear
2,692 posts
 
Shorting is a different can of worms. The output transformer makes a tube amp see a contant load even when shorted most of the time. This is why a speaker selector uses a transformer for multible speaker connections. But no load at all is a problem with tube amps. SS amps usually have protection for a no load situation.

This was borrowed from the Enjoy Music site.
"Note: Did you know that you should never turn on an amplifier in a system that is not connected to some type of load at the speaker terminals? Some amplifiers have built in protection for just this situation and some might not. The problem is no load means the amplifier might see an infinite load and may try to drive it. Of course an infinite load requires an infinite amount of power, which translates into heat. At a bare minimum most tube amplifiers have a resistor, which will melt and an open the circuit"
gs5556
769 posts
 
I would say it's very likely you damaged the output transformer. Never ever ever run a tube amp without a speaker or load resistor connected. The speaker impedance is reflected to the tube output via the transformer. No speaker means no load which means a short across the transformer.
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