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Gareth Magennis
 
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Default Fender "The Twin" Power resistor values?

Hi,

anyone know the values of the 10 Watt power resistors in the power supply of
"The Twin" that often burn out? The intact one here is 30K, the other is a
pile of carbon. Can't seem to find a schematic on the web.



Thanks,



Gareth.


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Don Pearce
 
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Default Fender "The Twin" Power resistor values?

On Fri, 31 Mar 2006 10:29:26 +0100, "Gareth Magennis"
wrote:

Hi,

anyone know the values of the 10 Watt power resistors in the power supply of
"The Twin" that often burn out? The intact one here is 30K, the other is a
pile of carbon. Can't seem to find a schematic on the web.

WHat is the exact model? They differ, but most power supply resistors
are about 10k.

d

Pearce Consulting
http://www.pearce.uk.com
  #3   Report Post  
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Gareth Magennis
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal" wrote in message
...
On Fri, 31 Mar 2006 09:36:47 GMT, (Don Pearce) wrote:

WHat is the exact model?


It's "The Twin", aka "Red Knob Twin".
An evolution of the classic Twin Reverb manufactured from 1987 to 1994.

http://www.ampwares.com/ffg/twin_redknob.html





Yep, thats the one, but I couldn't find its schematics.



Gareth.


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Don Pearce
 
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Default Fender "The Twin" Power resistor values?

On Fri, 31 Mar 2006 12:42:44 +0200, François Yves Le Gal
wrote:

On Fri, 31 Mar 2006 09:36:47 GMT, (Don Pearce) wrote:

WHat is the exact model?


It's "The Twin", aka "Red Knob Twin".
An evolution of the classic Twin Reverb manufactured from 1987 to 1994.

http://www.ampwares.com/ffg/twin_redknob.html

Sorry - I was going to offer you the same source as Flipper. If you
don't find exactly what you need, look through those for a schematic
that has the same output configuration as yours, and use the numbers
from there.

d

Pearce Consulting
http://www.pearce.uk.com
  #5   Report Post  
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Gareth Magennis
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal" wrote in message
...
On Fri, 31 Mar 2006 10:29:26 +0100, "Gareth Magennis"
wrote:

anyone know the values of the 10 Watt power resistors in the power supply
of
"The Twin" that often burn out? The intact one here is 30K, the other is
a
pile of carbon.


The only two 10-watt resistors in the PS are R128 = 2.7 K and R129 =30 K
so
the pile of carbon must be R128...

Can't seem to find a schematic on the web.


Hmmm. Try http://www.blueguitar.org/new/schem/fender/the_twin.gif
A low quality scan, but quite readable.





That's the one I want, thanks, and it is quite readable.


Gareth.




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Gareth Magennis
 
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Default Fender "The Twin" Power resistor values?


"Don Pearce" wrote in message
...
On Fri, 31 Mar 2006 10:29:26 +0100, "Gareth Magennis"
wrote:

Hi,

anyone know the values of the 10 Watt power resistors in the power supply
of
"The Twin" that often burn out? The intact one here is 30K, the other is
a
pile of carbon. Can't seem to find a schematic on the web.



Thanks,



Gareth.


OK - found it now:

http://www.blueguitar.org/new/schem/fender/the_twin.gif

d

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




Thanks for your perseverance Don, didn't know about blueguitar. Francois
was right, there's a pair of 30K and 2K7 10 Watters next to each other.



Gareth.


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Gareth Magennis
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal" wrote in message
...
On Fri, 31 Mar 2006 12:00:45 +0100, "Gareth Magennis"
wrote:

Francois
was right, there's a pair of 30K and 2K7 10 Watters next to each other.


I would do a thorough check on the amp: the two resistors are B+ droppers
for the preamp/phase splitter and shouldn't dissipate more than 3 or 4
watts. If a 10-watt R has burned, something must be very wrong somewhere
else.





No doubt. I was assuming an output tube, but I see you're right about that
resistor only supplying the preamps.
Interestingly it has a set of Mesa 5881-6L6 tubes (STR 425). Are these 5881
or 6L6?! I understand 5881 cannot take the same plate voltage.


Thanks,


Gareth.


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Gareth Magennis
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal" wrote in message
...
On Fri, 31 Mar 2006 14:11:35 +0100, "Gareth Magennis"
wrote:

Interestingly it has a set of Mesa 5881-6L6 tubes (STR 425). Are these
5881
or 6L6?!


They are neither.

In Mesa Boogie's parlance :

STR 425 = relabeled 6pi33C., a Russian equivalent of the 5881,
manufactured
by Reflektor and identical to the Sovtek-branded 5881WXT version. The
6pi33C
is quite a poor match with Fender Twin Reberb like circuits and iron BTW:
max output power is limited and tone if far from optimal.

STR 430 = Russian take of the 6L6GC, also manufactured by Reflektor and
identical to the Sovtek 6L6WXT+ version.

The Twin is designed around real 6L6GC's. When the 5881's die, you should
try some Svetlana SED (circle C logo - not the winged S, which are
rebadged
Sovetk's, again) 6L6GC's or the excellent Shuguang Chinese version under
the
TAD 6L6GC-STR moniker , which give some of the best results in this amp
type.




Glad you said that, the Svetlanas Circle C are what I use.





BTW, STR originally meant "Special Test Requirement". This label was only
applied to fully tested and graded tubes targeting critical applications.
It
doesn't mean the same nowadays and only designates tested and matched
tubes.

I understand 5881 cannot take the same plate voltage.


B+ is aournd 470 V in high power mode, with around - 60 V bias. the output
tubes see less than 410 V with around 40 ma of current, well into the SOA
of
a 6pi33C.






Thanks for the lesson, much appreciated.




Gareth


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Phil Allison
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal"

was right, there's a pair of 30K and 2K7 10 Watters next to each other.


I would do a thorough check on the amp: the two resistors are B+ droppers
for the preamp/phase splitter and shouldn't dissipate more than 3 or 4
watts. If a 10-watt R has burned, something must be very wrong somewhere
else.



** Nonsense.

That POS 30 kohm resistor Fender used runs very hot, cracks apart,
unsolders itself and eventually fails completely in normal use.

Best to replace it with a 50 watt "metal clad" type, bolted to the
chassis.

Eg:

http://au.farnell.com/jsp/endecaSear...jsp?SKU=345726



........ Phil




  #10   Report Post  
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Phil Allison
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal"


The Twin is designed around real 6L6GC's.



** I don't think so.

The Red Knob Twin or "The Twin" ( aka The Evil Twin ) was designed in
1989/90 as a replacement for the 135 watt "ultra-linear" Twin Reverb which
had been designed around the Sylvania/Philips ECG 6L6GC tube - really the
same up-rated tube as the 7027.

By 1989 the Sylvania 6L6GC / 7027 tubes were no longer in production, nor
were similar tubes from GE. Hence - the Red Knob Twin was designed DOWN to
take the then available Chinese made 6L6GC tubes, most of which were of
truly awful quality.

IME Sovtek brand and other Russian made 5881s work very well in the Red
Knob Twin - but not so good in the 135 watt "Twin Reverb" models.


I understand 5881 cannot take the same plate voltage.



** Plate voltage is not the problem issue.

Plate dissipation, peak plate current and excessive screen supply voltage
are.



........ Phil








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Ft.peoplepc.com
 
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Default Fender "The Twin" Power resistor values?

"Phil Allison" wrote in message ...

"François Yves Le Gal"

was right, there's a pair of 30K and 2K7 10 Watters next to each other.


I would do a thorough check on the amp: the two resistors are B+ droppers
for the preamp/phase splitter and shouldn't dissipate more than 3 or 4
watts. If a 10-watt R has burned, something must be very wrong somewhere
else.



** Nonsense.

That POS 30 kohm resistor Fender used runs very hot, cracks apart, unsolders itself and eventually fails completely in normal
use.

Best to replace it with a 50 watt "metal clad" type, bolted to the chassis.


Well, by the voltages on the schematic the 30K dissipates over 5W, so a 10W
resistor is under-rated and should be replaced by a higher power unit. An ordinary
25W device should do if there is adequate air flow to cool it, else a bolt-on metal
resistor as Phil suggests would be a better solution.

But the resistor that burned in this amp was the 2.7K 10W that normally only
dissipates about 2W. If the following 2.2K 1W isn't also burnt, about the only
likely culprit would be a leaky or shorted C116, the 22uf 450V cap at that point.
Once that's fixed, another 2.7K 10W replacement should be fine.

Regards,
Fred

Eg:

http://au.farnell.com/jsp/endecaSear...jsp?SKU=345726



....... Phil






  #12   Report Post  
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Phil Allison
 
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Default Fender "The Twin" Power resistor values?


"Ft.peoplepc.com"


But the resistor that burned in this amp was the 2.7K 10W that normally
only
dissipates about 2W.



** Nope.

See:

http://www.blueguitar.org/new/schem/fender/the_twin.gif


When the amp is used in "low power" mode, the voltage across that 2.7
kohms rises to circa 100 volts - makes it dissipate 4 watts.

PLUS it is mounted on a PCB, side by side and in contact with the very hot
running 30 kohms one.

PLUS there is SFA air flow in the chassis.

Once the 30 kohms is on its own, bolted to the chassis, life is sweet for
the 2.7 kohms one.




......... Phil







  #13   Report Post  
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Phil Allison
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal"
"Phil Allison"


** Replacing the ** CONTEXT ** some frog asshole snipped out of sight.


" *** The Twin is designed around real 6L6GC's.*** "



The Red Knob Twin or "The Twin" ( aka The Evil Twin ) was designed in
1989/90


It was maketed between 1987 and 1994.



** Not going by the published schematics.



Hence - the Red Knob Twin was designed DOWN to
take the then available Chinese made 6L6GC tubes, most of which were of
truly awful quality.



The Twin was fitted with selected rebranded Chinese tubes,



** Backs my point up entirely !!

Those Chinese made 6L6GCs were anything but " .... real 6L6GCs"

Performance and reliability were just appalling.



IME Sovtek brand and other Russian made 5881s work very well in the Red
Knob Twin - but not so good in the 135 watt "Twin Reverb" models.


They don't: they aren't 5881's and mismatch the output iron.



** They do.

There is no impedance mismatch.

Only ****ing ******s use idiotic terms like "output iron".





......... Phil


  #14   Report Post  
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Phil Allison
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal" = an ass.


That POS 30 kohm resistor Fender used runs very hot, cracks apart,
unsolders itself and eventually fails completely in normal use.


The defective R is the 2,7 K, not the 30 K.



** Try putting the original CONTEXT back - you pile of frog ****.

Also, try reading my other post on the same matter.





......... Phil



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Gareth Magennis
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal" wrote in message
...
On Fri, 31 Mar 2006 12:00:45 +0100, "Gareth Magennis"
wrote:

Francois
was right, there's a pair of 30K and 2K7 10 Watters next to each other.


I would do a thorough check on the amp: the two resistors are B+ droppers
for the preamp/phase splitter and shouldn't dissipate more than 3 or 4
watts. If a 10-watt R has burned, something must be very wrong somewhere
else.






Found the problem - the reverb tray input coil (8 ohm) was shorted. The 2K7
resistor supplies the reverb transformer primary via the 12AT7 driver, which
I have now replaced. Now just waiting for another tray. Incidentally I
have never been able to find these values in 10 Watts here in the UK, I used
to have to get them from Fender. The 2k7 is now a 22K and 3k3 in parallel.


Thanks to all,


Gareth.




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Phil Allison
 
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Default Fender "The Twin" Power resistor values?


"Gareth Magennis"


Found the problem - the reverb tray input coil (8 ohm) was shorted.



** Bull****.

It normally measures less than 1 ohm on a DC meter.



The 2K7 resistor supplies the reverb transformer primary via the 12AT7
driver, which I have now replaced.



** Yawn......


Now just waiting for another tray.




** Why ?????????????????????????????

Reverb tank drive coils NEVER fail short.


YOU are a ASININE PITA ****WIT !!!!!





............ Phil


  #17   Report Post  
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Phil Allison
 
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Default Fender "The Twin" Power resistor values?


"François Yves Le Gal"

Which gives 2K87, not a significant difference. Current balance between
the
two R's won't be a problem.



** Shame how folk taking any notice of a lying pile of sub human wog ****
will.







........... Phil


  #18   Report Post  
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Gareth Magennis
 
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Default Fender "The Twin" Power resistor values?


"Phil Allison" wrote in message
...

"Gareth Magennis"


Found the problem - the reverb tray input coil (8 ohm) was shorted.



** Bull****.

It normally measures less than 1 ohm on a DC meter.



The 2K7 resistor supplies the reverb transformer primary via the 12AT7
driver, which I have now replaced.



** Yawn......


Now just waiting for another tray.




** Why ?????????????????????????????

Reverb tank drive coils NEVER fail short.


YOU are a ASININE PITA ****WIT !!!!!





........... Phil




Phil, when you have knowledge that can correct other peoples mistakes, why
do you let yourself get so angry about it? Nobody likes that behaviour and
it doesn't do you any good in the long run either. Despite some of your
unforgivable behaviour, some people, inclucing me, have respect for your
knowledge and the occasional glimpses of you trying to help people with it.
Nobody respects you when you use your experience to arrogantly and
childishly attack others, and your attempts at racism do not belong anywhere
on the internet.

As usual, you are right, I measured the 8 ohm coil at about 0.8 ohms and
assumed it was damaged. You could have stepped in and pointed out my error
in a civilised manner but regretfully chose not to. But no matter, I have
learned something new, which IMO is what usenet is all about, and I have
told you before that I don't find your attempted insults insulting in the
least, just really rather bizarre and illogical behaviour, so ranting any
more just isn't going to do it for you I'm afraid.


I'll put my money on the 12AT7 going faulty then. I did measure a partial
short to chassis with it plugged in and powered down, and assumed the
shorted coil had killed it, or some combination of the two had occurred.




Gareth.





Gareth.
















  #19   Report Post  
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Phil Allison
 
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Default Fender "The Twin" Power resistor values?


"Gareth Magennis"

Found the problem - the reverb tray input coil (8 ohm) was shorted.



** Bull****.

It normally measures less than 1 ohm on a DC meter.


The 2K7 resistor supplies the reverb transformer primary via the 12AT7
driver, which I have now replaced.



** Yawn......


Now just waiting for another tray.



** Why ?????????????????????????????

Reverb tank drive coils NEVER fail short.


YOU are a ASININE PITA ****WIT !!!!!


( snip pile of half witted abuse)


** Hey Gareth !

Go shove you pompous and idiotic opinions where the sun don't shine.


As usual, you are right, I measured the 8 ohm coil at about 0.8 ohms and
assumed it was damaged.



** First YOU assumed a complete nonsense, then acted on that assumption,
ordered an expensive part and THEN boasted here about it. Just like the
PITA, narcissistic, ****** you are.



You could have stepped in and pointed out my error in a civilised manner
but regretfully chose not to.



** You are in NO position to criticise or talk down to those trying to
advise YOU.

I find YOUR attitude extremely offensive.

If you want to know something - then ASK !!

If you think you already know - then **** OFF.



BTW

Guitar amp repairs are not the topic of this NG.

**** off back to AGA or where ever it is that crackpots & fools advise
****wits like you how to screw up their amplifiers and electrocute
themselves.




......... Phil




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