Surface maount and valves/tubes.

[N_Cook]

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/

 

[N_Cook]

boardjunkie <boardjunkie@techie.com> wrote in message
news:c4bff98a-cacf-4f63-9b34-6f37c6d2eb97@b1g2000hsg.googlegroups.com...
On Jul 23, 9:00 am, "N_Cook" <dive...@tcp.co.uk> 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/

 

[Arfa Daily]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:g67plu$vf3$1@registered.motzarella.org...

boardjunkie <boardjunkie@techie.com> wrote in message
news:c4bff98a-cacf-4f63-9b34-6f37c6d2eb97@b1g2000hsg.googlegroups.com...
On Jul 23, 9:00 am, "N_Cook" <dive...@tcp.co.uk> 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

 

[N_Cook]

(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 use

agreed 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
http://home.graffiti.net/diverse:graffiti.net/

 

[Dave]

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:g67a1u$qs0$1@registered.motzarella.org...

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.

 

[Meat Plow]

On Wed, 23 Jul 2008 14:00:13 +0100, 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.

No more problematic than valve sockets soldered into a PCB. What valves
are they, EL84s?

 

[boardjunkie]

On Jul 23, 9:00 am, "N_Cook" <dive...@tcp.co.uk> 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.....