2. amps-preamps
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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
rwwear
2,871 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
1,235 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.
elevick
2,636 posts
 
Did you try switching the tubes from the right to left and vice versa? Replacing a tube is a lot easier/cheaper.
Make sure you turn off the amp first and don't burn yourself either!
mechans
3,048 posts
 
Yes your amp sleeps with the fishes. No load is seen by the amp as no impedance except the cable. We all no that you created an impedance mismatch, tubes love impedance the higher the strain on the tube to transmit it's energy the load has to be close to the tubes output or it create a form of fusion and melt the tubes glass which why a tube amp can't run without being coupled to a transformer. Atmasphere and those other companies that don't have autoformers are just a myth. In truth you could have a very bad explosion because the mismatch also cause the reversal of the physical vacuum the tube must have for the electron to fly from one plate to the other. Bummer
irbow OP
4 posts
 
Well, thanks for the responses, I guess I should take it to a repairer. I'm Ok with a soldering iron but I would need to know where to start.

Iain
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