Just repaired a tube amp , problem unrelated to this. But it seemed odd to me to have valves , in inverted orientation , ie under a pcb with SM resistors on it.
Anyone foresee temperature cycling problems/ dislodged SMD in the future with such arrangements.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
As they say "If it can be done, some fool will do it". Given that heat rises, I see no benefit whatsoever to putting a tube which converts 70% of the electricity fed through it to heat underneath a PCB. All it's going to do is shorten the life of the PCB components and, quite possibly, the tube. There's a reason why most tube amps have the tubes exposed or covered only by a mesh grille...
just my 2 cents.
What the hell kind of amp was it??? Just so I can refuse repairs on that kind of garbage.....
on
What the hell kind of amp was it??? Just so I can refuse repairs on that kind of garbage.....
Laney LC15 from 2002
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
No more problematic than valve sockets soldered into a PCB. What valves are they, EL84s?
Well, I think maybe you've answered your own question there. If it has done six years so far without a problem of the type you are envisaging, I doubt that it's going to develop one. Those sm resistors are subjected to a lot of heat and various levels of thermal cycling when they are first fitted, that's a lot more intense than anything that the valves are going to generate in normal service. Many amps that I work on, have the output valves fitted upside down in a pcb-mounted holder, and it doesn't seem to cause a problem with either the service life of the valves, or the pcb above them. I have, however, had bad joints on the output valve holders of several Fenders recently, that have been manufactured with lead-free solder. I don't know if this is as a result of thermal cycling or not, but I rather suspect that it is a 'normal' lead-free production problem that we are getting used to seeing on all sorts of equipment, now.
Arfa
(reply to lost original)
I wonder which is nore punishing
2 extreme temp cycling with no vibration at manufacture or thousands of medium temp cycling with vibration in useagreed lead-free solder thrown into the equation makes that temp/vibration situation more problematic
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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