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In Reply to: panic-help!!! My almost new 275 has popping noises posted by Duilawyer on February 8, 2007 at 21:29:07:
Is this an original MC275 or a relatively new one? There are now 5 different generations of this amp spanning about 40 years.Snapping and popping isn't unusual in a tube amp, first off. Depending on age, however, it can be sourced from a number of places. This is where the exact age of the amp is helpful.
Cheers,
Follow Ups:
this one has the five way binding posts, they have only been shipped since Dec. AND (I fell like an ahole) the problem, seems to have gone for the moment. Two mintues after I wrote a scathing email to the seller. But this hissing and popcorn popping lasted 3 hours at least, and the popping, maybe onc evry few minutes , was withthe unit from the start. AFTER, the unit suddenly stopped making the noises, I still switched some tubes (I had spare 12ax7s and 12AT7s!) and it is playing now, and I ma waiting for the dreaded noise. So fr good thirty minutes. DAMAGE to a tube from my quad speakers doing a crowbar shutdown, which they did Wedneday when I got the unit first hooked up? Damage to the unit form the crowbar shutdown?? :-( !!!
I think what you're experiencing here is just a bad tube pin to socket connection, and from the amount of noise and the reaction of your speaker'protection circuitry, I would guess that the bad connection is in the front end...the 12AX7 voltage gain section. It's sort of counterintuitive, but when you get a dirty connection like this on the socket of a power tube, often all that happens is that the tube turns red at the plate. There is no change in the sound at all. But in a big amp, the front end does most of the voltage gain. Consequently, any little arcing is dutifully amplified and travels downstream where it becomes an enormous noise. Cleaning the sockets and cleaning the pins may be your solution. It's scary sounding, but not really a big deal.
Boy do I feel like a axxhxxe.
...You're just caught up in the thrill of a new source of enjoyment and want it to be perfect. Nothing makes a man so tall as when he stoops to say he's sorry.
nt
what I wrote the seller:I apologize for jumping the gun. it looks like it was a minor repair. I apologize for my attitude but you have to admit that
sale was very bizarre. So when my new amp started
making popcorn noises, I assumed the worst. I
apologize for my attitude.It looks like replacing 4 tubes(!) has fixed the
problem, it now has six hours on the new tubes with no
noises. Maybe one got damaged during packing or during
my drive home. I hope my poor attitude and suspicion did not offend you to where you cannot forgive my rudeness.
I will keep it. It certainly
sounds heavenly when there are no noises, like now.
The shutdown circuit of the Quad would not damage an amp, unless the amp is poorly designed. When the protection circuit is engaged, the Quad presents a 1.5ohm to the amp. It only lasts a few seconds.Any tube amp should handle this without issue. Any good solid state amp should also have no problems with the Quad protection circuit.
that came loose during transit?
If and when the spirit moves you, you might eventually try the Penta Labs KT88SC tubes. Great tubes.
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