Hi everyone,
I made a trade for a pair of preowned Quicksilver Mono amps on the weekend. One amp makes an odd noise a few seconds after it is turned on. It only lasts a second then goes away, so I'm not sure if it's something I should be concerned about. It's a mechanical "whumm" sound and isn't coming from speakers. Kind of sounds like a lightsaber from Star Wars, lol. I've attached a video so you can hear it. The noise happens 12 seconds in.
Any idea what might cause this noise? I think it's one of the transformers, but I'm not sure. Amp seems fine otherwise, but I'm worried it could lead to bigger problems down the road if not dealt with. I also emailed Quicksilver, but thought I'd ask here as well in case I don't hear back from them. The seller said I could return amps if I'm not happy, so I'd like to make a decision soon.
Thanks very much.
I made a trade for a pair of preowned Quicksilver Mono amps on the weekend. One amp makes an odd noise a few seconds after it is turned on. It only lasts a second then goes away, so I'm not sure if it's something I should be concerned about. It's a mechanical "whumm" sound and isn't coming from speakers. Kind of sounds like a lightsaber from Star Wars, lol. I've attached a video so you can hear it. The noise happens 12 seconds in.
Any idea what might cause this noise? I think it's one of the transformers, but I'm not sure. Amp seems fine otherwise, but I'm worried it could lead to bigger problems down the road if not dealt with. I also emailed Quicksilver, but thought I'd ask here as well in case I don't hear back from them. The seller said I could return amps if I'm not happy, so I'd like to make a decision soon.
Thanks very much.
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First thing I thought…“Wow that’s kind of cool!” LOL
I have a pair of Quicksilver horn monos…never experienced this or any other turn on/off thumps.
My first guess would be some kind of in rush current…isn’t that what usually causes power on/off noises?
The brainy guys will chime in soon enough…good luck!
I have a pair of Quicksilver horn monos…never experienced this or any other turn on/off thumps.
My first guess would be some kind of in rush current…isn’t that what usually causes power on/off noises?
The brainy guys will chime in soon enough…good luck!
Sounds like a power transformer with loose windings or being stressed in some way. Might be a bad rectifier giving the power transformer fits. Try swapping the rectifier tubes from one amp to another. Could also be a bad power supply capacitor. They load those GZ34s with a LOT of capacitance.
Thanks for the quick replies. The rectifier tubes are the 5AR4s, right? Edit... just realized GZ34 and 5AR4 are same. I'll try swapping them.
IIRC, Quicksilver are a bit notorious for large caps right after the rectifier.
What model number are these amps? Maybe someone can find a schematic.
jeff
What model number are these amps? Maybe someone can find a schematic.
jeff
The tag on back says Model: Mono Amp. I just swapped the tubes and noise moved to the other amp. I also noticed one the "bad" tubes is 5U4M, and the other 3 are 5AR4. Could that tube be the problem?
Yes, that could be the issue. I've experienced the same sort of noise switching from a 5AR4 to a 5U4GB.
BTW, DO NOT buy JJ 5AR4 rectifier tubes for those amps.
jeff
That 5U4M is actually a Russian 5Y3, which is not an appropriate rectifier for that amp. It's a directly-heated rectifier, which means a fast turn on. It's also barely adequate for service in that amp. So, you're getting an unbalanced "half-wave" surge in the problem amp, which will not make the transformer happy. It would be wise to get four fresh 5AR4s to make sure the rectification is balanced. Pricey, I know, but it'll prolong the use of those amps. At the very least, make sure you've got strong 5AR4s in all four sockets.
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I just replaced that 5U4M tube with a 5AR4 I pulled from my Scott amp. That got rid of the startup noise. I'm glad it was an easy fix and will look for a replacement, maybe all four. Thanks for the tip about the JJs. Any recommendations for something that won't cost a fortune?
I would just do the "yellow sheet" mod to your amps, unless someone here has a good reason not to. That will prolong the life of those 5AR4's.
jeff
jeff
Agree. The high inrush current would cause the power transformer to vibrate excessively, causing a mechanical type of hum. This is true when silicon rectifiers are used. I wouldn't expect that if vacuum tube rectification were used, since the tube's heater warm up time provides a soft start that would eliminate that. Another remote possibility is that if the amplifier has a push-pull output stage, and one of the two output tubes starts to conduct before the other does, then there would be hum that would fade out once the 2nd tube starts to conduct current. This could happen if tubes of different brands or ages were used in the output stage.
Post number 32 if memory is correct.
I've had a few pairs of the Quicksilver mono block amps. One pair of the KT88's like you purchased. As mentioned they do eat the rectifier tubes unless you add the diodes as shown in post #32 of my thread above. With the mod they will last for years.
The design of the Quicksilver is flawed because the size of the filter cap exceeds the rectifier rating. Before doing the mod I actually watched a pair of rectifier tubes flash with brilliant light a split second before the amp died.
Wait a minute, that can't be right, can it? You're shorting the high-voltage primaries together that way. The 5AR4s are wired in parallel, one tube acting as a single diode for each leg of the secondary. Those crossed diodes are not needed.
I think the biggest problem was the sudden current draw on only one leg of the secondary, causing a huge imbalance between the two secondary legs, exceeding the secondary current rating and stressing the tranny.
It's supposed to be, but I don't think it's correct. The crossed diodes are not needed and may hurt the transformer. Otherwise, yes, a pair of UF4007 diodes in series with each 5AR4 would reduce the strain on the tubes. In this case, the diodes are doing the rectifying and the 5AR4s are pretty much just providing the slow warm-up.
Would a 1N4007 diode work for this application instead of UF4007? I was going to order a replacement tube from Parts Connexion here in Canada and they have 1N4007 available, but not the other. I was doing some searching online about this and found responses like this "There are differences. These differences are terribly important in some circuit applications, but completely insignificant in other circuit applications. It depends."
UF4007s (ultrafast) are quieter but with the tube buffer it probably won't matter, so 1N4007s are fine. You can find the UF variety at Mouser or Digikey.