Surface maount and valves/tubes.
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 http://home.graffiti.net/diverse:graffiti.net/ |
Surface maount and valves/tubes.
"N_Cook" wrote in message ... 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. 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. |
Surface maount and valves/tubes.
On Jul 23, 9:00*am, "N_Cook" wrote:
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 onhttp://home.graffiti.net/diverse:graffiti.net/ What the hell kind of amp was it??? Just so I can refuse repairs on that kind of garbage..... |
Surface maount and valves/tubes.
boardjunkie wrote in message
... On Jul 23, 9:00 am, "N_Cook" wrote: 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 onhttp://home.graffiti.net/diverse:graffiti.net/ 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 http://home.graffiti.net/diverse:graffiti.net/ |
Surface maount and valves/tubes.
"N_Cook" wrote in message ... boardjunkie wrote in message ... On Jul 23, 9:00 am, "N_Cook" wrote: 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 onhttp://home.graffiti.net/diverse:graffiti.net/ 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 http://home.graffiti.net/diverse:graffiti.net/ 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 |
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