Recent Marshall amps - safety issue.

[jakdedert]

Arfa Daily wrote:

"Gareth Magennis" <sound.service@btconnect.com> wrote in message >> Gareth
Magennis wrote:


I repair a LOT of Marshalls. I can't remember ever seeing a pot that has
been turned around on its mounting. Plenty that have got bashed from the
front or the shaft broken off, and possibly some that have actually been
turned with too much force, and the pot has disintegrated internally
instead.

Sure, make something better where it is appropriate, and with the
appropriate skills and method, which I often do. Lashing a whole bunch of
pots with a whole bunch of cable ties does not fit in with my version of
appropriate. Sound more like some over enthusiastic bodging. I would not
be pleased to see that on my amp, car, bicycle, chimney stack, cat, etc.



Gareth.

We see a lot of poor design these days, but I think in the end, we just have
to live with it. Today, for instance, I had a 'modern' version of the Vox
AC15 on the bench. For a start, you can't even get at the output valves,
without removing the chassis, so that's not too clever for 'on the road'
maintenance for a start. The problem with this particular amp was that the
sound was very 'thin', and there was a substantial amount of hum
continuously present. When I had the chassis out, it was clear that one of
the output valves was seriously distressed, with its anode glowing red hot.
I reached for my meter and probed the control grid pin on the affected
valve, and the wire just fell off. These are chassis mounted valve bases,
with wires going back to the nearby pcb, and what sort of wire have they
used ? Thin single strand, about like telephone extension wire. The wire had
neatly broken just at the end of the insulation.

Current capacity's probably all right. The Chinamen probably nicked it
with the strippers. That said, stranded would be more reliable. As to
the tubes being inside...that's just wrong. Does it say 'No user
replaceable parts inside. Refer all servicing to qualified personnel'?

jak

 

[Michael A. Terrell]

N Cook wrote:

A fudge fix there would be replace the defective wire and dabs of RTV on the
exposed ends of the remaining ones.

The proper repair would be to replace all the questionable wire while
it is on your bench.


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[jakdedert]

Michael A. Terrell wrote:

N Cook wrote:
A fudge fix there would be replace the defective wire and dabs of RTV on the
exposed ends of the remaining ones.


The proper repair would be to replace all the questionable wire while
it is on your bench.


Doing that--especially if the entire unit is 'questionable'--is not

always proper. Well, it's 'proper' in the sense that it's the right way
to repair something; but improper if the client is not willing to pay
for the bench time. On most gear the cost would exceed the value of the
finished product. As a business, you can't afford to re-engineer every
piece of gear that comes across your bench, at your own expense.

Better to fix the obvious problems, explain that it may reoccur and hand
it back...or forgo any repair at all. With just about *everything*
these days being engineered to the bottom line, you've just hit on the
reason for the demise of the local repair shop.

jak

 

[Michael A. Terrell]

jakdedert wrote:

Michael A. Terrell wrote:
N Cook wrote:
A fudge fix there would be replace the defective wire and dabs of RTV on the
exposed ends of the remaining ones.


The proper repair would be to replace all the questionable wire while
it is on your bench.


Doing that--especially if the entire unit is 'questionable'--is not
always proper. Well, it's 'proper' in the sense that it's the right way
to repair something; but improper if the client is not willing to pay
for the bench time. On most gear the cost would exceed the value of the
finished product. As a business, you can't afford to re-engineer every
piece of gear that comes across your bench, at your own expense.

Better to fix the obvious problems, explain that it may reoccur and hand
it back...or forgo any repair at all. With just about *everything*
these days being engineered to the bottom line, you've just hit on the
reason for the demise of the local repair shop.

Didn't he say it was a few solid wires going from the tube socket to
a PC board? That shouldn't take much longer than smearing RV all over
the terminals. If it was more than that, I would show the customer what
cause the problem and either get permission for a proper repair, or have
them sign off that you are not responsible for future problems. That
was the way I did things, and had bands riving 60 miles to find my small
shop. The only reason I had to quit was my failing health. No one ever
questioned me, and most told me to just do whatever was needed to make
it as reliable as possible. My industrial and commercial sound
customers needed things to work 24/7/365.25, and the bands didn't want a
failure that could cost them future bookings.


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The first sign of insanity is denying that you're crazy.

 

[boardjunkie]

On Sep 4, 9:01 pm, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

We see a lot of poor design these days, but I think in the end, we just have
to live with it. Today, for instance, I had a 'modern' version of the Vox
AC15 on the bench. For a start, you can't even get at the output valves,
without removing the chassis, so that's not too clever for 'on the road'
maintenance for a start.

Ugh.....don't get me started on those China reissues......

 

[boardjunkie]

On Sep 6, 9:35 pm, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

"boardjunkie" <boardjun...@techie.com> wrote in message

news:4bc58128-c7e9-4126-84a5-ba19b4582121@m73g2000hsh.googlegroups.com...
On Sep 4, 9:01 pm, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

We see a lot of poor design these days, but I think in the end, we just
have
to live with it. Today, for instance, I had a 'modern' version of the Vox
AC15 on the bench. For a start, you can't even get at the output valves,
without removing the chassis, so that's not too clever for 'on the road'
maintenance for a start.

Ugh.....don't get me started on those China reissues......

Which are, never-the-less, still supposedly designed here in the UK by a
company who should know better, after how long they've been in the business,
would you not agree ?

Arfa

I believe the original Jennings/Vox versions were the same way as far
as where the tube sockets are located. Its just the general
construction/layout inside the chassis that sucks rocks, although the
originals had thier issues as well. If I had one I'd likely gut it and
do a clean PTP rebuild.