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Old 28th December 2003, 10:41 PM   #1
lpd is offline lpd  Canada
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Default Quicksilver?

I recently acquired a pair of KT88 monoblocks. When operating the trannies hum a little (no hum from speakers, just trannies). Both amps have same amount of hum, is this normal? Otherwise great sounding amps.
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Old 29th December 2003, 07:05 AM   #2
SHiFTY is offline SHiFTY  New Zealand
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A lot of transformers hum in normal conditions. If they don't get hot and the hum isn't too loud, they are probably fine.

You could try tightening the bolts on them, or putting rubber dampers underneath them, but if its not too loud then just sit back and enjoy the music!
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Old 29th December 2003, 12:19 PM   #3
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I have three sets and all have a very slight hum when you put your ear next to them. Exercise caution when doing this as a hot tube can result in burned ear.

J
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Old 29th December 2003, 03:16 PM   #4
lpd is offline lpd  Canada
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The transformers don't get hot at all, slightly warm thats it. I ran them all day and as they warmed up a little the hum lessened. So after they cooled down I tightened them down and the hum has decreased quite a bit.

Burned what bias do you run yours?

The fellow I traded these from indicated 50ma, but I find 55ma sounds better and the company suggests 60ma per tube. He also installed a choke under the deck to save tube life. Only mod done and they operate 100%.
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Old 29th December 2003, 09:35 PM   #5
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On the actual KT88 versions they recommend 120mA. I run about 110mA in hope of prolonging the output tubes. On my 8417 conversions that I use either 6550's or KT 88's in I run 100mA. In actual distortion tests the higher bias will lower the distortion somewhat.

J
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Old 30th December 2003, 01:53 AM   #6
lpd is offline lpd  Canada
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What type of rectifier do you use ie. brand? The fellow I acquired the amps from stated that they were hard on rectifiers and didn't know what brand worked best. One blew a fuse on initial startup, but hasn't since. He recommended a variac to ramp up voltage?
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Old 31st December 2003, 12:07 PM   #7
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lpd

My quicksilvers use either NOS GE 5AR4's or Sovtek brand. Mine have a slight modification in the power supply which involves adding some 1N4007 diodes. These diodes take the brunt of the load and the rectifiers smooth out the peaks. The result is nice bass without the worries of arcing of the rectifiers. If you do a search here you will find several topics on Quicksilvers and there will be a power supply schematic of the modification there. Hope this helps!

J
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Old 31st December 2003, 09:07 PM   #8
lpd is offline lpd  Canada
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Hey what size and type of fuses does your KT88 amps use? Mine has 3 amp fast blows and one blows out from time to time if I turn on the amp too quickly. Would a slow blow fuse be appropriate?

Thanks


Peter
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Old 31st December 2003, 09:41 PM   #9
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Hi,

Quote:
Mine has 3 amp fast blows and one blows out from time to time if I turn on the amp too quickly. Would a slow blow fuse be appropriate?
If the fuse is on the primary side of the powerxformer it should be a slow blow type.

Cheers,
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Old 31st December 2003, 10:50 PM   #10
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If you have a good digital volt meter ,check your ac mains to make sure that the dc level is 1 volt or less . Hi dc levels will make the core laminations buzz .
Mark
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