Broken large ceramic Rs in combos

[N Cook]

So many of these lead failures, not solder problems
There must be a better way - at production, yes, using large diameter hollow
tube "beefings" and larger pcb solder pads and holes.
But retrofit ?
I'm assuming the oscillation mode is transverse to the resistor axis rather
than axially rocking. If laid against the pcb then the ceramic "feet" act as
leverage when rocking and if elevated off the board then extra momentum also
amplify the rupture force at the point where the leads go through the board.
This is my latest attempt. I have hundreds of these hermaphroditic
Varelco, Elco, Edac (DERA company, over-shelflife disposal) like in pic
http://www.dhaen.org.uk/vdocs/Onryoku2_files/varelco.jpg
(in the bag )
I could find no other pics on the net.
The flat part is the mating part so they can mate like 2 finfgers of one
hand rotated 90 degrees and mating twith 2 fingers of your other hand, so no
male/female specificity. A pair of these gold plated brass contacts with one
of the 2 fingers cut off with snips . Matching side with side so when
crimped and soldered to the resistor leads , facing opposite directions,
they are, locked against rocking, against the board.
It will still be a weak point at or in the pcb hole but will they be more
resistant to fracture than the usual resistor lead metal ?

 

[Ron(UK)]

So many of these lead failures, not solder problems
There must be a better way - at production, yes, using large diameter hollow
tube "beefings" and larger pcb solder pads and holes.
But retrofit ?
I'm assuming the oscillation mode is transverse to the resistor axis rather
than axially rocking. If laid against the pcb then the ceramic "feet" act as
leverage when rocking and if elevated off the board then extra momentum also
amplify the rupture force at the point where the leads go through the board.
This is my latest attempt. I have hundreds of these hermaphroditic
Varelco, Elco, Edac (DERA company, over-shelflife disposal) like in pic
http://www.dhaen.org.uk/vdocs/Onryoku2_files/varelco.jpg
(in the bag )
I could find no other pics on the net.
The flat part is the mating part so they can mate like 2 finfgers of one
hand rotated 90 degrees and mating twith 2 fingers of your other hand, so no
male/female specificity. A pair of these gold plated brass contacts with one
of the 2 fingers cut off with snips . Matching side with side so when
crimped and soldered to the resistor leads , facing opposite directions,
they are, locked against rocking, against the board.
It will still be a weak point at or in the pcb hole but will they be more
resistant to fracture than the usual resistor lead metal ?

Mount the resistor in a custom build anodised aluminium cradle, perched
on small springs with tiny hydraulic dampers to absorb any shock. Note
that the springs will need to be thermally insulated from the resistor
cradle to avoid any possibility of temper change through heat transference.

Hard wire the resistor to the board with mil spec extra flexible cable.
http://www.awcwire.com/ProductSpec.aspx?id=Rope-QQ-B-575

The connections should be both spot welded and soldered. The soldered
connections being made in accordance with NASA specifications -
available here http://www.hq.nasa.gov/office/codeq/sldrbch1.pdf

Re designating the guitar combo as military or aviation equipment will
allow you to use tin/lead solder as per NASA specs

Hope this Helps

Ron(UK)

 

[Arfa Daily]

Mount the resistor in a custom build anodised aluminium cradle, perched on
small springs with tiny hydraulic dampers to absorb any shock. Note that
the springs will need to be thermally insulated from the resistor cradle
to avoid any possibility of temper change through heat transference.

Hard wire the resistor to the board with mil spec extra flexible cable.
http://www.awcwire.com/ProductSpec.aspx?id=Rope-QQ-B-575

The connections should be both spot welded and soldered. The soldered
connections being made in accordance with NASA specifications - available
here http://www.hq.nasa.gov/office/codeq/sldrbch1.pdf

Re designating the guitar combo as military or aviation equipment will
allow you to use tin/lead solder as per NASA specs

Hope this Helps

Ron(UK)

Oh Ron, you naughty little tinker you ... :~)

Arfa

 

[Ron(UK)]

Oh Ron, you naughty little tinker you ... :~)

Well personally, I just resolder them.

Ron(UK)

 

[N Cook]

Well personally, I just resolder them.

Ron(UK)

Perhaps it was you who "repaired" this Fender previously.
I don't like bouncing repairs in the complaint sense.
Whoever, resoldered an already weakened ceramic W/W lead so it broke in the
pcb hole this time.
Perhaps multi-stranded copper wire bulked up with swathing in solder is the
material of choice for these component leads.
Obviously coppery metal work hardens and fractures, brass probably does too
if it moves.
What metal of small cross section that is solderable, not corrodable , and
survives vibration/oscillation/work hardening ?

 

[msg]

So many of these lead failures, not solder problems
There must be a better way - at production, yes, using large diameter hollow
tube "beefings" and larger pcb solder pads and holes.
But retrofit ?

<snip>

I like to use gold-plated square posts on the pcb and salvaged Berg
female connector pins on the fragile components leads; shock, flexing
and vibration will produce other failure modes before ruining a
part so mounted.

Regards,

Michael

 

[Meat Plow]

Mount the resistor in a custom build anodised aluminium cradle, perched
on small springs with tiny hydraulic dampers to absorb any shock. Note
that the springs will need to be thermally insulated from the resistor
cradle to avoid any possibility of temper change through heat transference.

Hard wire the resistor to the board with mil spec extra flexible cable.
http://www.awcwire.com/ProductSpec.aspx?id=Rope-QQ-B-575

The connections should be both spot welded and soldered. The soldered
connections being made in accordance with NASA specifications -
available here http://www.hq.nasa.gov/office/codeq/sldrbch1.pdf

Re designating the guitar combo as military or aviation equipment will
allow you to use tin/lead solder as per NASA specs

Hope this Helps

Ron(UK)

LOL!

 

[Meat Plow]

So many of these lead failures, not solder problems
There must be a better way - at production, yes, using large diameter hollow
tube "beefings" and larger pcb solder pads and holes.
But retrofit ?
I'm assuming the oscillation mode is transverse to the resistor axis rather
than axially rocking. If laid against the pcb then the ceramic "feet" act as
leverage when rocking and if elevated off the board then extra momentum also
amplify the rupture force at the point where the leads go through the board.
This is my latest attempt. I have hundreds of these hermaphroditic
Varelco, Elco, Edac (DERA company, over-shelflife disposal) like in pic
http://www.dhaen.org.uk/vdocs/Onryoku2_files/varelco.jpg
(in the bag )
I could find no other pics on the net.
The flat part is the mating part so they can mate like 2 finfgers of one
hand rotated 90 degrees and mating twith 2 fingers of your other hand, so no
male/female specificity. A pair of these gold plated brass contacts with one
of the 2 fingers cut off with snips . Matching side with side so when
crimped and soldered to the resistor leads , facing opposite directions,
they are, locked against rocking, against the board.
It will still be a weak point at or in the pcb hole but will they be more
resistant to fracture than the usual resistor lead metal ?

I guess they just don't make them like they used to? I've worked on many
many combo amps and can only recall one failure as you describe and it was
in my own Peavey Artist 120 circa 1975.

 

[Ron(UK)]

I guess they just don't make them like they used to? I've worked on many
many combo amps and can only recall one failure as you describe and it was
in my own Peavey Artist 120 circa 1975.

I bet that happened because the white gluey stuff they put on to
stabilise the part had dried out and cracked off, same goes for the
smoothing caps. I usually stabilise them with a squirt of high temp hot
melt glue, the woodworking stuff. When it gets hot it goes softer, but
doesn't run off like the clear type does.

I service amps that travel the length and breadth of the country
virtually non stop being professionally used. These failures are just a
part of life, beefing up one area probably means that something else
will fail elsewhere. Plus of course, modern stuff is junk compared to
that which was made 20/30/40 years ago

All IMHO of course

Ron(UK)

 

[Meat Plow]

I bet that happened because the white gluey stuff they put on to
stabilise the part had dried out and cracked off, same goes for the
smoothing caps. I usually stabilise them with a squirt of high temp hot
melt glue, the woodworking stuff. When it gets hot it goes softer, but
doesn't run off like the clear type does.

Seems to have been the cause of the failure IIRC. Have you used silicone
rubber? Seems like it would be a good choice.

I service amps that travel the length and breadth of the country
virtually non stop being professionally used. These failures are just a
part of life, beefing up one area probably means that something else
will fail elsewhere. Plus of course, modern stuff is junk compared to
that which was made 20/30/40 years ago

All IMHO of course

IMHO too.

 

[N Cook]

<snip>

I like to use gold-plated square posts on the pcb and salvaged Berg
female connector pins on the fragile components leads; shock, flexing
and vibration will produce other failure modes before ruining a
part so mounted.

Regards,

Michael

Snap: I use what I think is the UK equivalent , 2 or 3 QM female pins slid
over the long wire of on-end large Rs to make more rigid when soldered in.
Can anyone identify the square section pins C,D,E in
http://home.graffiti.net/diverse:graffiti.net/varelco2.jpg
probably wire-wrap pins (1mm squares).
They are all much more rigid than the usual coppery wire leads to ceramic
Rs.
A and B are the Varelco pins that when one blade is cut off give a good
rigid mount when placed in opposite sense to block "rock and roll"

 

[N Cook]

news:[email protected]...

graph paper is 1mm squares

 

[Ron(UK)]

Seems to have been the cause of the failure IIRC. Have you used silicone
rubber? Seems like it would be a good choice.

Yes, silicone bath sealer works also . It just takes longer to set and
they might be a slight risk of corrosion from the acetic acid, tho
having said that, I`ve seen whole pcb`s potted in the stuff.

Ron(UK)

 

[Meat Plow]

Yes, silicone bath sealer works also . It just takes longer to set and
they might be a slight risk of corrosion from the acetic acid, tho
having said that, I`ve seen whole pcb`s potted in the stuff.

The SMEC out of my 88 Dodge Dakota was potted in silicone. I've seen it
used in ham radio gear and some amps.

 

[Arfa Daily]

I bet that happened because the white gluey stuff they put on to stabilise
the part had dried out and cracked off, same goes for the smoothing caps.
I usually stabilise them with a squirt of high temp hot melt glue, the
woodworking stuff. When it gets hot it goes softer, but doesn't run off
like the clear type does.

I service amps that travel the length and breadth of the country virtually
non stop being professionally used. These failures are just a part of
life, beefing up one area probably means that something else will fail
elsewhere. Plus of course, modern stuff is junk compared to that which
was made 20/30/40 years ago

All IMHO of course

Ron(UK)

I too mend a lot of this gear, and for sure, you are right that the modern
stuff, whilst being relatively just as expensive as that which was made in
the 60s and 70s, is nowhere near as well built. That said, I too agree that
failures of joints and leads on wirewound resitors is just par for the
course with the stuff - as was, as is, and as ever will be. I really don't
look on it as a big problem, and I'm sure that the musos just treat it all
as part of the rich tapestry of life on the road. If they haven't got a
spare amp with them, they just jack into the bass player's or whatever.
Whilst I would never just 'repair' a leg that had broken, as I'm sure that
Ron probably doesn't either, I'm sure that if the job is done properly, you
are not going to get a bounce, that is going to reflect badly on you. I
certainly don't see returns from doing such jobs.

I always enjoy Cooky's posts, and some of the fixes he comes up with, but
really, I do sometimes think that he is seeing problems that really don't
exist, and then finding fixes for them. Sorry mate, and no offense
intended - just the way I see it. :~)

Arfa

Arfa

 

[Arfa Daily]

Yes, silicone bath sealer works also . It just takes longer to set and
they might be a slight risk of corrosion from the acetic acid, tho having
said that, I`ve seen whole pcb`s potted in the stuff.

Ron(UK)

I used to pot a whole board that I used to make for a company, in a
'flowing' silicon rubber. It got in and around and under every component on
the board, and then cured just like bath sealer, but without the acetic acid
smell. It was designed for electronic potting, so I guess it was corrosion
proof.

Arfa

 

[Meat Plow]

I used to pot a whole board that I used to make for a company, in a
'flowing' silicon rubber. It got in and around and under every component on
the board, and then cured just like bath sealer, but without the acetic acid
smell. It was designed for electronic potting, so I guess it was corrosion
proof.

Isn't 100% pure silicon just that? Or is silicon naturally acetic? Would
"corrosion proof" silicon have an additive?

 

[Arfa Daily]

Isn't 100% pure silicon just that? Or is silicon naturally acetic? Would
"corrosion proof" silicon have an additive?

I think that the acetic acid thing is something to do with the curing
process. Presumably, this stuff used a different chemistry to arrive at the
result of it setting. I seem to recall it was a Dow Corning product, that I
bought from one of the big electronic component suppliers. It came in a
cartridge that you put in a standard builder's 'gun'. Came out of the nozzle
with about the consistency of treacle, and just flowed around the board and
self levelled. After about a half hour, during which time you had to keep an
eye on it to make sure that it wasn't running off the edge of the board, it
had gone to a sort of soft jelly state, and had skinned over. You could then
just leave it overnight, and by the next morning, it had gone off to that
really tough, but still flexible state, that you find where they've used
such stuff as the insulating infill on FBTx's and triplers and the like.
Unlike bath sealer, it stuck like shit to a blanket, and had a really strong
peel resistance. There was no chance of repairing a board that had been
covered with it - ever ...

The board was a counter that I was 'ringing' for a friend's company, and
this protection method was what was used originally, so I just copied it.
The counter was on food processing machines which operated in a refrigerated
and generally hostile environment that was subject to washing down by hose,
so the board had to be totally proof against condensation and 'wet' water.

Arfa

 

[Ron(UK)]

Isn't 100% pure silicon just that? Or is silicon naturally acetic? Would
"corrosion proof" silicon have an additive?

Is it possible that the 'vinegar smell' is some kind of mould or fungus
inhibitor? I don't remember the original stuff we used to get from
RadioSpares having an acetic acid smell - but I could be mistaken, it
was a long time ago.

Ron(UK)

 

[Eeyore]

I understand that this may be PVA adhesive or something very similar.

same goes for the

Is it possible that the 'vinegar smell' is some kind of mould or fungus
inhibitor?

It is actually acetic acid AIUI. In the cheap 'bathroom' silicones it's what 'makes
it go off'. It's inadvisable to use this for electronics because of the acid fumes.

I don't remember the original stuff we used to get from
RadioSpares having an acetic acid smell - but I could be mistaken, it
was a long time ago.

Electronic grades use a different and more expensive activator.

I suspect the stuff Arfa's talking about is quite different. Does it set quite
hard ?

Graham