Ping Don..
 

(As opposed to *pinged off*?? :-)

As you're aboot Don Old...

I've emailed Nick Gorham to no effect (inconsiderate sod has probably
buggered off on holiday), so perhaps you could rummage your 'valve
savvy' and assist me with a problem?

I've got Tone The Clone's 300B monoblocs back again. I have previously
removed the volume pots and they were fine; then he put a 300B in in 90
degrees wrong and did one of them no favours at all. Swapping out a
suspicious-looking cap seemed to solve that one, but he has since
managed to accidentally interchange the rectifier and driver valves at
some stage - although the amp was (seemed) perfectly OK when I swapped
them back!!

Anyway, the amps have been superbly good for some weeks, but now the
'damaged' one of them is playing up again - the bias meter (s/b 75 mA
??) moves all the way up to max as the thing warms up and bad distortion
kicks in I'm told. Any immediate ideas where to look as to cause? I have
both amps here and can make comparison measurements - I'm told all the
passives measure OK...??

Here they are *again*

http://www.apah69.dsl.pipex.com/show...yAmpsAgain.JPG


If (with my zero knowledge) I can't bash 'em straight *with some
guidance*, they will end up at the local (shiny Nigel's) hifi shop for
the odious techie *Andrew* to sort them out and I don't think I could
stand the 'loss of face'...!!

:-)

Ping Don..
 

"Keith G" wrote in message
...

(As opposed to *pinged off*?? :-)

As you're aboot Don Old...

I've emailed Nick Gorham to no effect (inconsiderate sod has probably
buggered off on holiday), so perhaps you could rummage your 'valve
savvy' and assist me with a problem?

I've got Tone The Clone's 300B monoblocs back again. I have previously
removed the volume pots and they were fine; then he put a 300B in in
90 degrees wrong and did one of them no favours at all. Swapping out a
suspicious-looking cap seemed to solve that one, but he has since
managed to accidentally interchange the rectifier and driver valves at
some stage - although the amp was (seemed) perfectly OK when I swapped
them back!!

Anyway, the amps have been superbly good for some weeks, but now the
'damaged' one of them is playing up again - the bias meter (s/b 75 mA
??) moves all the way up to max as the thing warms up and bad
distortion kicks in I'm told. Any immediate ideas where to look as to
cause? I have both amps here and can make comparison measurements -
I'm told all the passives measure OK...??

Here they are *again*

http://www.apah69.dsl.pipex.com/show...yAmpsAgain.JPG


If (with my zero knowledge) I can't bash 'em straight *with some
guidance*, they will end up at the local (shiny Nigel's) hifi shop for
the odious techie *Andrew* to sort them out and I don't think I could
stand the 'loss of face'...!!

:-)


Actually, it's even worse than that - I would like to rip all the 'bias
meter' palaver out of 'em and change them to cathode bias.

(No idea how to do that, needless to say!! :-)

Ping Don..
 

On Thu, 12 Jul 2007 14:42:35 +0100, "Keith G"
wrote:


(As opposed to *pinged off*?? :-)

As you're aboot Don Old...

I've emailed Nick Gorham to no effect (inconsiderate sod has probably
buggered off on holiday), so perhaps you could rummage your 'valve
savvy' and assist me with a problem?

I've got Tone The Clone's 300B monoblocs back again. I have previously
removed the volume pots and they were fine; then he put a 300B in in 90
degrees wrong and did one of them no favours at all. Swapping out a
suspicious-looking cap seemed to solve that one, but he has since
managed to accidentally interchange the rectifier and driver valves at
some stage - although the amp was (seemed) perfectly OK when I swapped
them back!!

Anyway, the amps have been superbly good for some weeks, but now the
'damaged' one of them is playing up again - the bias meter (s/b 75 mA
??) moves all the way up to max as the thing warms up and bad distortion
kicks in I'm told. Any immediate ideas where to look as to cause? I have
both amps here and can make comparison measurements - I'm told all the
passives measure OK...??

Here they are *again*

http://www.apah69.dsl.pipex.com/show...yAmpsAgain.JPG


If (with my zero knowledge) I can't bash 'em straight *with some
guidance*, they will end up at the local (shiny Nigel's) hifi shop for
the odious techie *Andrew* to sort them out and I don't think I could
stand the 'loss of face'...!!

:-)




Swapping those valves could easily have damaged something, because
they would have both been going flat out with nothing to limit the
anode current (neither grid would have been connected). Best I can
suggest is swapping valves between the two amps to see which one
carries the fault with it, then get a new one of those.

I haven't looked at the pinouts of the two to see what connects to
what when you swap them, but this is my best guess.

Passives damaged by too much current tend to show the evidence pretty
dramatically. But if it is a passive, measure the value of the cathode
resistor and make sure it hasn't gone low. Also measure the resistance
from grid to ground to check it isn't open circuit.

d

--
Pearce Consulting
http://www.pearce.uk.com

Ping Don..
 

Keith G wrote:
(As opposed to *pinged off*?? :-)

As you're aboot Don Old...

I've emailed Nick Gorham to no effect (inconsiderate sod has probably
buggered off on holiday),

Chance would be a fine thing. I never got your email Keith. Anyway....

I've got Tone The Clone's 300B monoblocs back again. I have previously
removed the volume pots and they were fine; then he put a 300B in in 90
degrees wrong and did one of them no favours at all. Swapping out a
suspicious-looking cap seemed to solve that one, but he has since
managed to accidentally interchange the rectifier and driver valves at
some stage - although the amp was (seemed) perfectly OK when I swapped
them back!!

Anyway, the amps have been superbly good for some weeks, but now the
'damaged' one of them is playing up again - the bias meter (s/b 75 mA
??) moves all the way up to max as the thing warms up and bad distortion
kicks in I'm told. Any immediate ideas where to look as to cause? I have
both amps here and can make comparison measurements - I'm told all the
passives measure OK...??

Here they are *again*

http://www.apah69.dsl.pipex.com/show...yAmpsAgain.JPG


If (with my zero knowledge) I can't bash 'em straight *with some
guidance*, they will end up at the local (shiny Nigel's) hifi shop for
the odious techie *Andrew* to sort them out and I don't think I could
stand the 'loss of face'...!!


Without knowing the circuit its a bit of a guess, but my first thought
would be to check if the coupling caps have become leaky. (assuming
there are any).

Check the voltage between the 300b grid and ground. I would expect
something like -70v. If the coupling cap is leaking it will be higher
than that.

Have you considered painting the valve bases and sockets so he may be
able to work out what goes where? Or faining that, strike hime on the
head with the nearest outout transformer and tell him to get a clue?

--
Nick

Ping Don..
 

Keith G wrote:
"Keith G" wrote in message
...

(As opposed to *pinged off*?? :-)

As you're aboot Don Old...

I've emailed Nick Gorham to no effect (inconsiderate sod has probably
buggered off on holiday), so perhaps you could rummage your 'valve
savvy' and assist me with a problem?

I've got Tone The Clone's 300B monoblocs back again. I have previously
removed the volume pots and they were fine; then he put a 300B in in
90 degrees wrong and did one of them no favours at all. Swapping out a
suspicious-looking cap seemed to solve that one, but he has since
managed to accidentally interchange the rectifier and driver valves at
some stage - although the amp was (seemed) perfectly OK when I swapped
them back!!

Anyway, the amps have been superbly good for some weeks, but now the
'damaged' one of them is playing up again - the bias meter (s/b 75 mA
??) moves all the way up to max as the thing warms up and bad
distortion kicks in I'm told. Any immediate ideas where to look as to
cause? I have both amps here and can make comparison measurements -
I'm told all the passives measure OK...??

Here they are *again*

http://www.apah69.dsl.pipex.com/show...yAmpsAgain.JPG


If (with my zero knowledge) I can't bash 'em straight *with some
guidance*, they will end up at the local (shiny Nigel's) hifi shop for
the odious techie *Andrew* to sort them out and I don't think I could
stand the 'loss of face'...!!

:-)



Actually, it's even worse than that - I would like to rip all the 'bias
meter' palaver out of 'em and change them to cathode bias.

(No idea how to do that, needless to say!! :-)


Again, depends on the circuit, you may not have enough B+ to do that.

--
Nick

Ping Don..
 

"Nick Gorham" wrote

Again, depends on the circuit, you may not have enough B+ to do that.


OK - that's a *secondary objective* atm!

(The meters have been swapped and both seem to be OK in the 'good' amp!)

Ping Don..
 

"Don Pearce" wrote in message
...
On Thu, 12 Jul 2007 14:42:35 +0100, "Keith G"
wrote:

a sorry tale


Swapping those valves could easily have damaged something, because
they would have both been going flat out with nothing to limit the
anode current (neither grid would have been connected). Best I can
suggest is swapping valves between the two amps to see which one
carries the fault with it, then get a new one of those.


No, all that's been tried - all/any of the valves (and the meter) can be
swapped to the good amp willy nilly and it continues to work perfectly.



I haven't looked at the pinouts of the two to see what connects to
what when you swap them, but this is my best guess.

Passives damaged by too much current tend to show the evidence pretty
dramatically. But if it is a passive, measure the value of the cathode
resistor


Seems OK/same on both amps.


and make sure it hasn't gone low. Also measure the resistance
from grid to ground to check it isn't open circuit.


OK, with no power on (?):

Good amp = 100 kOhm

'Bad' amp = 40 kOHm

??

Ping Don..
 

"Nick Gorham" wrote in message
. uk...
Keith G wrote:
(As opposed to *pinged off*?? :-)

As you're aboot Don Old...

I've emailed Nick Gorham to no effect (inconsiderate sod has probably
buggered off on holiday),

Chance would be a fine thing. I never got your email Keith. Anyway....


Direct response received and replied to!



If (with my zero knowledge) I can't bash 'em straight *with some
guidance*, they will end up at the local (shiny Nigel's) hifi shop
for the odious techie *Andrew* to sort them out and I don't think I
could stand the 'loss of face'...!!


Without knowing the circuit its a bit of a guess, but my first thought
would be to check if the coupling caps have become leaky. (assuming
there are any).


He has replaced the two 100 uF caps which I deem to be the coupling caps
with a single 220 uF cap on the 'bad' amp and it has been fine for a
while...



Check the voltage between the 300b grid and ground. I would expect
something like -70v. If the coupling cap is leaking it will be higher
than that.


OK - powered up with dummy loads.

Grid to Ground:

Good Amp - a *continually* changing 0.04 to 0.06 VDC

Bad Amp - steady 202 VDC (???)

Are we on the money so soon?



Have you considered painting the valve bases and sockets so he may be
able to work out what goes where? Or faining that, strike hime on the
head with the nearest outout transformer and tell him to get a clue?


Oh, he's learning!! - It doesn't help the bloody amps are *handed*!! :-)

They're both still on - are we doing further damage??

Ping Don..
 

"Keith G" wrote in message
...

"Don Pearce" wrote in message
...
On Thu, 12 Jul 2007 14:42:35 +0100, "Keith G"
wrote:

a sorry tale


Swapping those valves could easily have damaged something, because
they would have both been going flat out with nothing to limit the
anode current (neither grid would have been connected). Best I can
suggest is swapping valves between the two amps to see which one
carries the fault with it, then get a new one of those.


No, all that's been tried - all/any of the valves (and the meter) can
be swapped to the good amp willy nilly and it continues to work
perfectly.



I haven't looked at the pinouts of the two to see what connects to
what when you swap them, but this is my best guess.

Passives damaged by too much current tend to show the evidence pretty
dramatically. But if it is a passive, measure the value of the
cathode
resistor


Seems OK/same on both amps.


Additional:

*VDC* across the cathode resistors:

Good amp = 59VDC

Bad amp = 154 VDC

Does this add anything - certainly don't look right???

Ping Don..
 

"Keith G" wrote

Additional:

*VDC* across the cathode resistors:

Good amp = 59VDC

Bad amp = 154 VDC

Does this add anything - certainly don't look right???


Additional additional:

Anode voltages (amps are warm now)

Good boy = 438 VDC

Bad boy = 312 VDC

Both steady....

??