| lpd |
| 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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| ShiFtY |
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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| burnedfingers |
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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| lpd |
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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| burnedfingers |
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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| lpd |
| 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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| burnedfingers |
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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| lpd |
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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| fdegrove |
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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| battradio |
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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| lpd |
| If the dc is higher than 1 volt how would one rectify (no pun intended) the situation? Line conditioner? |
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| fdegrove |
Hi,
| quote: | | Hi dc levels will make the core laminations buzz . |
Sure....Thought about that too...
Cheers,;) |
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| lpd |
| quote: | Originally posted by battradio
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 |
hows about 5 volts!!!! I tried another plugg and it was considerably lee ie. .25 volts. |
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| fdegrove |
Hi,
| quote: | | If the dc is higher than 1 volt how would one rectify (no pun intended) the situation? Line conditioner? |
What you need is a DC-blocking circuit, something like this:
DC-BLOCK
Or this; I think I culled from Thorsten Loesch's site:
Cheers,;) |
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| lpd |
Just out of curiosity, will this dc current that causes hum the tranny ruin anything? Does it harm the amplifier in anyway?
Thanks
Peter |
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| fdegrove |
Hi,
| quote: | | Just out of curiosity, will this dc current that causes hum the tranny ruin anything? Does it harm the amplifier in anyway? |
No, I won't expect any downside to it in anyway.
Cheers, ;) |
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| battradio |
The 5 volts won't damage your transformers it's just annoying .The DC can be caused from another electric appliance,or a bad stepdown transformer on the power pole . It is likely only on one side of power line . About half the outlets will be on one side of the 240 volt circuit ,the others on the oposite side .try shuting off circuit beakers one at a time to see if it originates in your home and unpluging items on the offending circuit .
Mark |
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| lpd |
| How's about using an isolation tranny to filter out dc? Just a thought. |
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| fdegrove |
Hi,
| quote: | | How's about using an isolation tranny to filter out dc? Just a thought. |
How about finding the source of the DC leakage?
Cheers,;) |
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| lpd |
I'm looking, but its a very old house, with suites next door ect. and I may have to move to an isolation tranny if I can't find it. I've been hunting for days. All plugs have a 5 volt dc in them?
Also would a unit like this one be ok for soft start on my Quicksilver amps?
soft start unit |
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| fdegrove |
Hi,
| quote: | | I'm looking, but its a very old house, with suites next door ect. and I may have to move to an isolation tranny if I can't find it. I've been hunting for days. All plugs have a 5 volt dc in them? |
Comes a day that my fliyng over will be cheaper than calling in the help of a qualified electrician...
Either way, it's no solution to your problem....The proplem must be somewhere down your supply.
| quote: | | Also would a unit like this one be ok for soft start on my Quicksilver amps? |
If you use the 5AR4 you HAVE a soft start already....the DC filter won't change that....
Cheers, ;) |
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