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A cautionary tale.

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A cautionary tale.

Postby ef37a » Mon Nov 12, 2018 7:19 am

I was recently contacted by a guitar amp tech I chat to in Scotland who had a problem with an HT-60 Stage combo. The fault was very weak output volume even at high settings.

Long-short..The fault turned out to be a crimp connector in the speaker circuit gone high resistance, poorly done crimp. Tech stripped and soldered the wire and all was well.

But! This could easily have been an expensive disaster. Obviously the amp was being driven with next to no load and it is a wonder the OP valves survived, not to say the OP traff.

The moral I hope is clear. Especially with a valve amp. CHECK THE SPEAKER CIRCUIT first.

Dave.
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Re: A cautionay tale.

Postby Martin Walker » Mon Nov 12, 2018 2:46 pm

Ouch!

I always thought crimp connectors were fairly foolproof, as they relied on physical effort or a special tool to join the two parts, so the two metal parts were 'squashed' into place.

Mind you, that doesn't stop the occasional leakage problems with a crimped Cornish pasty :beamup:


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Re: A cautionay tale.

Postby Sam Spoons » Mon Nov 12, 2018 3:18 pm

They are widely used on aircraft so must be considered pretty reliable but I have experienced corrosion issues using them in car and boat electrics.
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Re: A cautionay tale.

Postby Hewesy » Mon Nov 12, 2018 4:08 pm

As an aside I think that's why the aircraft industry developed ACF50, to avoid that corrosion risk especially in cabling between skins or outside of the heated cabin element.

Not sure I'd use it on guitar amp cabling but it's fantastic stuff to have around especially for bike parts and anything metal that lives outdoors.

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Re: A cautionary tale.

Postby Hugh Robjohns » Mon Nov 12, 2018 4:10 pm

Sam Spoons wrote:They are widely used on aircraft so must be considered pretty reliable but I have experienced corrosion issues using them in car and boat electrics.

I believe they are mandated on aircraft wiring looms and elsewhere, not least because if made correctly, the joint is inherently hermetically sealed and thus immune to internal corrosion problems.

The problem, of course, is that making a crimp joint correctly requires a dedicated tool for the specific wire and connectors, and a properly trained operator -- things which aren't always available....

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Re: A cautionary tale.

Postby Sam Spoons » Mon Nov 12, 2018 4:23 pm

How true, a friend was an engineer on commercial aircraft and had the kit (which we used on a couple of cars we were working on back in the day) He always used to point out that there isn't a hard shoulder up there....... :smirk:
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Re: A cautionary tale.

Postby ef37a » Mon Nov 12, 2018 7:52 pm

It is Sod's Law of course that the tech that had the fault has a deep and enduring hatred of any connection that isn't soldered and regularly condemns crimp spade connections.

I have had an email back from the Blackstar service tech and he tells me that he has never had any problems with the connectors at all. Neither did I and as others have pointed out, they are virtually universal in cars and domestic appliances and give virtually no bother at all.

I think I know the reason for his prejudice however? The technical term for it is, Crap. The chap has seen all sorts of gear over a lifetime of fixing and there have been some RIGHT dogs of amplifiers! My reposte to him is always (we are perfectly happy to disagree to disagree. He openly tells me he does not like the sound of the amps either!) Any technology, no matter how intrinsicly "good" can be made bad by poor materials or shoddy workmanship.

The point was also made here that tooling must be appropriate and operation intelligent.
Then, crimping 6mm spades is not much of an effort if you are doing ten an hour restoring your beloved E type but 1000 crimps or so before lunch means the last 100 might not get the full "oumph"? Some things ARE better done by robots.

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Re: A cautionary tale.

Postby Wonks » Mon Nov 12, 2018 8:08 pm

Also 6mm spades are too large for most speaker connections, which normally need 4.3mm ones.
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Re: A cautionary tale.

Postby ef37a » Mon Nov 12, 2018 8:16 pm

Wonks wrote:Also 6mm spades are too large for most speaker connections, which normally need 4.3mm ones.

Yes, Celestion especially. Many people are also unaware that the receptacle should be fitted such that the hole in the spade can be acessed with a spike to facilitate removal?

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Re: A cautionary tale.

Postby resistorman » Tue Nov 13, 2018 12:32 am

When I lived on a small tropical island I encountered many problems with crimped connections, so I always am suspicious. Everywhere else it hasn’t been much of a problem.
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Re: A cautionary tale.

Postby IvanSC » Wed Nov 21, 2018 7:27 pm

Heh - when we brought my wifes american Ford Escort back from a 4 year stay in Corsica (tiny island in the Mediterranean) the day after we arrived in England, the doors and locks on said doors had all rusted so much overnight that we struggled to open them the next morning!

NOW tell me the UK isnt damp. :D
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