Hello, just completed the bias on my tube amp, is it ok if one of the tubes have a very slight glow in the middle of it? You can only see the glow if the lights are off in the room (totaly dark). As well the amp sounds fine, and it takes about 10-15 minutes for this to happen. If the lights in the room are on, can't see the glow. The tubes are 6550's if that matters.
Thanks
Rino Odorico
Thanks
Rino Odorico
Hello Rino,
From the info you provide it's really hard to tell.Probably a slight mismatch between the two tubes ?
It won't kill'em though.
If you care to send more precise info ? Have you measured the current ?
Rgds,
From the info you provide it's really hard to tell.Probably a slight mismatch between the two tubes ?
It won't kill'em though.
If you care to send more precise info ? Have you measured the current ?
Rgds,
No, I haven't checked the current (don't actually know how to), I have the service manual for this amp (Luxman MQ-360), what it calls for is to check the DC voltage and adjust between 5.3 ~ 5.9 volts. My voltage readings are a bit high...6.4 is the lowest I can get it, don't know why...changed all of the caps, trans. are good...even replaced the bias pots (same value) and only changed for the better about 1/2 volt.
The glow I am explaining is a sight redness in the middle of the tube...only shows with the lights off. Also tubes are a Matched quad from Sovetek 6550's.
BTW, plate volatage is 450VDC
Thanks Rino Odorico
The glow I am explaining is a sight redness in the middle of the tube...only shows with the lights off. Also tubes are a Matched quad from Sovetek 6550's.
BTW, plate volatage is 450VDC
Thanks Rino Odorico
Rino,
I don't feel you have a problem to loose sleep over.
Still if you want to isolate the problem I suggest you swap the tubes's position around.
You would know for sure if the prob. lies with the tube or not.
Seems to me the matching was only so-so.
Rgds,
I don't feel you have a problem to loose sleep over.
Still if you want to isolate the problem I suggest you swap the tubes's position around.
You would know for sure if the prob. lies with the tube or not.
Seems to me the matching was only so-so.
Rgds,
Frank,
That sounds like a good idea, I'll try that this weekend. If the problem is still with the same tube socket and not with the tube itself, what do you think could be the problem?
Regards,
Rino Odorico
That sounds like a good idea, I'll try that this weekend. If the problem is still with the same tube socket and not with the tube itself, what do you think could be the problem?
Regards,
Rino Odorico
Rino,
Chances are 1/100.000 IMO.
In short my gut feeling tells me it's the tube NOT the amp.Try..
Rgds,
Chances are 1/100.000 IMO.
In short my gut feeling tells me it's the tube NOT the amp.Try..
Rgds,
One last question Frank
Hello Frank,
Thanks for all of your help. I just have one last question, so what it sounds like, having .5 to 1 volt difference on the bias is not that bad of a thing...so I shouldn't loose sleep over it then. As long as the amp doesn't blow fuses and sound like Jimi Hendrix has his guitar plugged into it, it's fine?
Rino Odorico
Hello Frank,
Thanks for all of your help. I just have one last question, so what it sounds like, having .5 to 1 volt difference on the bias is not that bad of a thing...so I shouldn't loose sleep over it then. As long as the amp doesn't blow fuses and sound like Jimi Hendrix has his guitar plugged into it, it's fine?
Rino Odorico
Rino,
My pleasure.
If yr. amp doesn't pop its fuses playing Jimmy at full blast consider yourself a very happy man...
Stop the acid,take some wee....
Rgds,
My pleasure.
If yr. amp doesn't pop its fuses playing Jimmy at full blast consider yourself a very happy man...
Stop the acid,take some wee....
Rgds,
I am willing to help you wid the bias problem... Check the value of the resistors connected to pin 8 and 1 to ground. Using ohms law V=I R , You can calculate the bias current by this method. Using voltmeter, measure the voltage on this resistor... example, if it is 100 ohm, then a 0.5 volt would correspond to a bias of of 50 milliampere.
Good Luck,
John
Good Luck,
John
Thanks John
Great, thanks John. I'll try that this weekend!
The amp still has a small glow to the tubes (I thought that it was just the one, but it's all of them...4-6550's). Strange, the glow is very slight and doesn't effect the sound of the amp. If anything it sounds like it has a little better bass. As well, I felt brave and had the amp on for 8 hours...the glow never increased, or decreased for that matter.
Regards,
Rino Odorico
Great, thanks John. I'll try that this weekend!
The amp still has a small glow to the tubes (I thought that it was just the one, but it's all of them...4-6550's). Strange, the glow is very slight and doesn't effect the sound of the amp. If anything it sounds like it has a little better bass. As well, I felt brave and had the amp on for 8 hours...the glow never increased, or decreased for that matter.
Regards,
Rino Odorico
You need to check the plate dissipation. You mentioned the Voltage is 450VDC (You measured this, right?)
For a 6550, the plate dissipation should be around 35W. Any higher and you will shorten the life of the tubes. The sound will be good... for a while. Could get expensive!
This means you should have a plate current of ~80 milliamps or less. If the amps are push pull, you can bias them colder than this. I assume you have some 6550 datasheets?
Did this only happen with the Sovtek tubes? They may not have a very high power handling....
For a 6550, the plate dissipation should be around 35W. Any higher and you will shorten the life of the tubes. The sound will be good... for a while. Could get expensive!
This means you should have a plate current of ~80 milliamps or less. If the amps are push pull, you can bias them colder than this. I assume you have some 6550 datasheets?
Did this only happen with the Sovtek tubes? They may not have a very high power handling....
