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Old 27th July 2011, 05:36 PM   #1
lpd is offline lpd  Canada
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Default Tube Preamp Question

Ok this may seem strange, but here is my dilemma....

Recently purchased a needs work 26 tube preamp. I noticed a channel was out and the socket for the power supply to preamp needed attention. Before repairing the preamp worked intermittently. I matched it with a Stax DA80 amp with very good results. Warm midrange, decent bass ect.

I had the socket solder reflowed on the umbilical cord from power supply to the pre, and put back into the system...now the pre is anemic, no midbass, and sounds unbalanced? Nothing else was touched just a octal socket reflow of solder. Any thoughts on this one? Of course I foolishly did not take voltage readings before reflowing solder so I don't have a benchmark for voltage readings.
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Old 27th July 2011, 05:38 PM   #2
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Unanswerable without pics.
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Old 27th July 2011, 05:43 PM   #3
DF96 is offline DF96  England
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By reflowing do you mean heat up each joint, and possibly add a bit more solder? If so, this is a good way to push a poor joint over the edge into being a bad joint. You can just about get away with reflowing on a freshly made joint which you are not quite happy with, but on an old joint it is a bad technique.
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Old 27th July 2011, 05:49 PM   #4
lpd is offline lpd  Canada
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hmmmm maybe stripping each connection down and resoldering is first in order. Prior to reheating solder the pre worked fine sans one tube filament would go out occasionally....wiggle the wire in the socket it would return. Now both tubes operate with no issues, just doesn't sound right.
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Old 27th July 2011, 06:53 PM   #5
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by lpd View Post
hmmmm maybe stripping each connection down and resoldering is first in order. Prior to reheating solder the pre worked fine sans one tube filament would go out occasionally....wiggle the wire in the socket it would return. Now both tubes operate with no issues, just doesn't sound right.
The simplest explanation is that it really does sound the same, you've only now noticed some defects. Next simplest is that you changed something else at the same time, maybe just the position of a speakers or whatever.

Last is that the re-flow really did change the sound. This is unlikely but just maybe the poor solder joint had some resistance in it and was doing a job like a "grid stopper" resistor or maybe changed a bias point by adding some resistance to a ground return. We'd need a schematic to make a better guess

Last edited by ChrisA; 27th July 2011 at 06:56 PM.
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