Laney Cub 12R

[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?



..... Phil

 

[tm]

** 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

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.

Is it RoHS?

 

[Phil Allison]

"tm"

"Phil Allison"

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.

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

 

[Phil Allison]

"Arfa Daily"

"Phil Allison"


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 ??

** Give that man a Kewpie doll.................

? 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 ...

** For some whacky reason, the Chinese included a PTC ( aka Polyswitch ) in
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

 

[josephkk]

"tm"


** 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.



... Phil

That sounds like it could easily be a dying polyfuse.

?-)

 

[Phil Allison]

"Arfa Daily"

"josephkk"
You must have Phil's personal posts blocked ?

** Errr - he just answered one ...




.... Phil