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Laney Cub 12R
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Phil Allison
Aug 11, 2013, 9:48:39 PM8/11/13
to
** Ever see one of these ?
An evil mix of EL84s, ECC83s and SMD on the same PCB.
Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
sockets.
But none of these were the problem.
The amp would run OK for about 10 mins and then power itself down - all the
lights go out and the sound fades away.
Turning the power off and waiting a few minutes restored operation, but not
for long.
Who has come across this one?
.... Phil
tm
Aug 12, 2013, 2:26:41 AM8/12/13
to
"Phil Allison" <phi...@tpg.com.au> wrote in message
news:b6qt7r...@mid.individual.net...
resistor that opens up with heat.
Maybe you can spray some freeze spray around to see if you can localize the
problem.
Is it RoHS?
Phil Allison
Aug 12, 2013, 5:13:29 AM8/12/13
to
"tm"
> "Phil Allison"
>>
>> ** Ever see one of these ?
>>
>> An evil mix of EL84s, ECC83s and SMD on the same PCB.
>>
>> Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
>> sockets.
>>
>> But none of these were the problem.
>>
>> The amp would run OK for about 10 mins and then power itself down - all
>> the lights go out and the sound fades away.
>>
>> Turning the power off and waiting a few minutes restored operation, but
>> not for long.
>>
>> Who has come across this one?
>>
>
>> ** Ever see one of these ?
>>
>> An evil mix of EL84s, ECC83s and SMD on the same PCB.
>>
>> Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
>> sockets.
>>
>> But none of these were the problem.
>>
>> The amp would run OK for about 10 mins and then power itself down - all
>> the lights go out and the sound fades away.
>>
>> Turning the power off and waiting a few minutes restored operation, but
>> not for long.
>>
>> Who has come across this one?
>>
>
> I have never seen one of those but a first guess, look for a cracked smd
> resistor that opens up with heat.
> Maybe you can spray some freeze spray around to see if you can localize
> the problem.
** All the clues are there.
> resistor that opens up with heat.
> Maybe you can spray some freeze spray around to see if you can localize
> the problem.
The amp powers itself off, valve heaters and the dial light goes out and
will not restart by itself.
A few minutes with the AC off does the trick.
... Phil
Arfa Daily
Aug 12, 2013, 6:28:42 AM8/12/13
to
news:b6rn9t...@mid.individual.net...
Sounds like it needs a good squib of WD40 to me, Phil ... :-)
But seriously, it's gotta be something to do with either that connector, SK4
that they've put in the way, or the PTC, F1 that follows it ?? Maybe faulty,
maybe hotting more than normal up for some reason ? Maybe had the wrong
pilot lamp fitted, although I would have expected the two 10 ohm Rs to have
taken care of that. Otherwise, apart from a heater in a valve going short to
a cathode maybe, about the only other thing is the hum balance pot, although
I'm not sure in what way practically that it could fail, to place an excess
load on the PTC ...
Arfa
But seriously, it's gotta be something to do with either that connector, SK4
that they've put in the way, or the PTC, F1 that follows it ?? Maybe faulty,
maybe hotting more than normal up for some reason ? Maybe had the wrong
pilot lamp fitted, although I would have expected the two 10 ohm Rs to have
taken care of that. Otherwise, apart from a heater in a valve going short to
a cathode maybe, about the only other thing is the hum balance pot, although
I'm not sure in what way practically that it could fail, to place an excess
load on the PTC ...
Arfa
Dave M
Aug 12, 2013, 6:32:46 AM8/12/13
to
I've never seen one of those units, but I'll take a guess that a PTC
resettable fuse is in the power transformer primary. It's clicking the set
off due to an overcurrent condition (bad transformer, filter caps,
rectifiers, etc.).
Dave M
Phil Allison
Aug 12, 2013, 6:44:48 AM8/12/13
to
"Arfa Daily"
> "Phil Allison"
>>>>
>>>> ** Ever see one of these ?
>>>>
>>>> An evil mix of EL84s, ECC83s and SMD on the same PCB.
>>>>
>>>> Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
>>>> sockets.
>>>>
>>>> But none of these were the problem.
>>>>
>>>> The amp would run OK for about 10 mins and then power itself down - all
>>>> the lights go out and the sound fades away.
>>>>
>>>> Turning the power off and waiting a few minutes restored operation, but
>>>> not for long.
>>>>
>>>> Who has come across this one?
>>>>
>>>>
>>>> ** Ever see one of these ?
>>>>
>>>> An evil mix of EL84s, ECC83s and SMD on the same PCB.
>>>>
>>>> Oh, and a DSP chip hiding on the back of a tiny PCB that holds 3 jack
>>>> sockets.
>>>>
>>>> But none of these were the problem.
>>>>
>>>> The amp would run OK for about 10 mins and then power itself down - all
>>>> the lights go out and the sound fades away.
>>>>
>>>> Turning the power off and waiting a few minutes restored operation, but
>>>> not for long.
>>>>
>>>> Who has come across this one?
>>>>
>> ** All the clues are there.
>>
>> The amp powers itself off, valve heaters and the dial light goes out and
>> will not restart by itself.
>>
>> A few minutes with the AC off does the trick.
>
>
>>
>> The amp powers itself off, valve heaters and the dial light goes out and
>> will not restart by itself.
>>
>> A few minutes with the AC off does the trick.
>
>
> Sounds like it needs a good squib of WD40 to me, Phil ... :-)
** LOL !!
>
> But seriously, it's gotta be something to do with either that connector,
> SK4 that they've put in the way, or the PTC, F1 that follows it ??
>? Maybe faulty, maybe hotting more than normal up for some reason ? Maybe
>had the wrong pilot lamp fitted, although I would have expected the two 10
>ohm Rs to have taken care of that. Otherwise, apart from a heater in a
>valve going short to a cathode maybe, about the only other thing is the hum
>balance pot, although I'm not sure in what way practically that it could
>fail, to place an excess load on the PTC ...
>
series with the 6.3 volt AC heater supply - adding to their bad judgement,
they picked one with too low a current rating.
The heater draw in the Cub 12R is a tad over 3 amps ( = 20 watts) and is
the largest load on the AC tranny.
Seems these Polyswitch devices deteriorate with age, if run hot all the
time - until they trip and go high resistance. With no heater supply, the
dial lamp goes out and the amp goes slowly silent and the same scenario can
be repeated indefinitely.
From reading the Laney user's forum, the fault is endemic with the model and
you need to fit a 6 amp rated PTC to fix it for sure.
Or just leave it out.
... Phil
Arfa Daily
Aug 12, 2013, 7:24:08 AM8/12/13
to
news:b6rsl4...@mid.individual.net...
Interestingly, on the schematic copy that I have, it shows F1 as a linear
thermistor which has the designation "PTC 6.0" by the side of it, which
would imply that it is specced as a 6 amp device. However, a little further
up the schematic in the AC feeds to the opamp supply rectifiers, there are
two more devices, this time shown as fuses with the component references F2
and F3, and designated as "PolySW0.3" which would imply to me that these are
300mA opening-current devices, and that Laney believe them to be a different
thing altogether from a PTC ?? Although polyswitches are of course PTCs,
they are designed to be very fast. On the other hand, there are positive
temperature coefficient thermistors that are similarly 'slow' to NTC ones.
There are plenty of characteristic graphs on the web showing 'slow' linear
PTC thermistor action, and others showing fast PTC polyswitch action.
Although that said, I don't really know why Laney would have designed one
into there anyway. An NTC thermistor to mitigate heater surge when they are
cold, maybe, but a PTC - linear characteristic or polyswitch
characteristic - seems altogether 'wrong' in that position, and I agree with
you that it's probably best just bypassed ...
Arfa
thermistor which has the designation "PTC 6.0" by the side of it, which
would imply that it is specced as a 6 amp device. However, a little further
up the schematic in the AC feeds to the opamp supply rectifiers, there are
two more devices, this time shown as fuses with the component references F2
and F3, and designated as "PolySW0.3" which would imply to me that these are
300mA opening-current devices, and that Laney believe them to be a different
thing altogether from a PTC ?? Although polyswitches are of course PTCs,
they are designed to be very fast. On the other hand, there are positive
temperature coefficient thermistors that are similarly 'slow' to NTC ones.
There are plenty of characteristic graphs on the web showing 'slow' linear
PTC thermistor action, and others showing fast PTC polyswitch action.
Although that said, I don't really know why Laney would have designed one
into there anyway. An NTC thermistor to mitigate heater surge when they are
cold, maybe, but a PTC - linear characteristic or polyswitch
characteristic - seems altogether 'wrong' in that position, and I agree with
you that it's probably best just bypassed ...
Arfa
dave
Aug 12, 2013, 11:28:48 AM8/12/13
to
components.
Arfa Daily
Aug 12, 2013, 12:55:47 PM8/12/13
to
"dave" <rick...@earthlink.net> wrote in message
news:Z8-dnfT6KM-tYpXP...@earthlink.com...
vapourise pretty instantly, and the Q-Tip would likely scorch ! :-)
Arfa
josephkk
Aug 14, 2013, 10:39:03 PM8/14/13
to
?-)
Arfa Daily
Aug 15, 2013, 4:26:45 AM8/15/13
to
"josephkk" <joseph_...@sbcglobal.net> wrote in message
news:520c3f47$0$58621$c3e8da3$12bc...@news.astraweb.com...
Arfa
Phil Allison
Aug 15, 2013, 6:50:18 AM8/15/13
to
"Arfa Daily"
> "josephkk"
> You must have Phil's personal posts blocked ?
** Errr - he just answered one ...
... Phil
Arfa Daily
Aug 15, 2013, 12:08:43 PM8/15/13
to
news:b73q3c...@mid.individual.net...
Well, yes, but I wondered in that case why he did not see the detailed
response that you gave to my reply, telling all about the polyfuse.
Sometimes, people that have blocked you see your posts as a result of the
original text appearing within someone else's post that's not blocked, but
again, I guess that he could have seen your reply in the response that I
posted after, without cutting any of your text ...
Life's full of mysteries ... :-)
Arfa
>
response that you gave to my reply, telling all about the polyfuse.
Sometimes, people that have blocked you see your posts as a result of the
original text appearing within someone else's post that's not blocked, but
again, I guess that he could have seen your reply in the response that I
posted after, without cutting any of your text ...
Life's full of mysteries ... :-)
Arfa
>
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