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Is my bias pot installed correctly.
Posted: Sun Dec 10, 2006 12:11 pm
by justonwo
As you can see, all three lugs on the bias pot are soldered into the "triangle" of lugs on the board. The thing I don't get is that you have buss wire from the lug closest to the front of the amp to the middle lug on the board. And you have a connection through the pot. Are you supposed to have two parallel connections here?
The way I have it wired, the pot changed the bias voltage successfully from -30 to -50 VDC, but I'm having problems with red plating tubes (reference the other thread). Have I wired it correctly?
http://www.the-byline.com/misc/100%20Wa ... %20059.jpg
http://www.the-byline.com/misc/100%20Wa ... %20060.jpg
http://www.the-byline.com/misc/100%20Wa ... %20061.jpg
Posted: Sun Dec 10, 2006 1:01 pm
by Flames1950
Yes it's correct.
Posted: Sun Dec 10, 2006 1:18 pm
by justonwo
Hmmm . . . I can't figure out for the life of me what's wrong with my amp then. Very strange plate glowing problem.
Posted: Sun Dec 10, 2006 5:56 pm
by Flames1950
Have you run it without the attenuator? (I think you said you were plugged into a 'Plate......) There's threads here and at Plexi Palace of guys who have redplating problems plugged into an attenuator, that don't show up when not using one.
Posted: Mon Dec 11, 2006 12:27 pm
by justonwo
I'll try that tonight. Do you think JJs might be more resistant to red plating than SEDs?
Flames, check out this post from a while back. This person is complaining about the same thing that's happening to me, and it seems by the end of his post that a cold solder joint on one of his 1 ohm resistors was to blame. Is this possible??
http://forum.metroamp.com/viewtopic.php ... 4e6f783988
Posted: Mon Dec 11, 2006 4:16 pm
by Flames1950
Sure.......I've also had trouble with either a cold joint or questionable resistor on pin 5 before. But you replaced the grid resistors to pin 5 of each tube already if I'm not mistaken........
Posted: Mon Dec 11, 2006 4:21 pm
by justonwo
Yep, I already replaced the grid resistors to pin 5. Is there any easy way to check for a cold solder joint or is it simply the appearance of the solder that gives it away (dull gray vs. shiny silver)?
Posted: Mon Dec 11, 2006 6:04 pm
by Flames1950
Turn the chassis upside down and turn it on, then CAREFULLY poke at each joint with something nonconductive, like a chopstick or Sharpie marker or pencil. When you find one that makes funny pops when you poke it, mark it with the Sharpie and resolder it later after the amp is off and the caps are drained.
Take note that your grid wires (green on the preamp tubes and the green/orange to the power amp tubes) may make some noise anyway, but it should be fairly soft......
Re: Is my bias pot installed correctly.
Posted: Wed Jul 06, 2022 3:38 pm
by uiovbged332