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Fender "The Twin" Power resistor values?



 
 
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  #1  
Old March 31st 06, 10:29 AM posted to rec.audio.tubes
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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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  #2  
Old March 31st 06, 10:36 AM posted to rec.audio.tubes
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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  
Old March 31st 06, 11:48 AM posted to rec.audio.tubes
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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.


  #4  
Old March 31st 06, 11:49 AM posted to rec.audio.tubes
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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  
Old March 31st 06, 11:54 AM posted to rec.audio.tubes
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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.


  #6  
Old March 31st 06, 12:00 PM posted to rec.audio.tubes
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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.


  #7  
Old March 31st 06, 02:11 PM posted to rec.audio.tubes
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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.


  #8  
Old March 31st 06, 03:18 PM posted to rec.audio.tubes
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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


  #9  
Old April 1st 06, 03:50 AM posted to rec.audio.tubes
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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  
Old April 1st 06, 05:54 AM posted to rec.audio.tubes
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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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