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Post subject: Re: fender twin reverb 1965 reissue problem update with pic
Posted: Mon Jan 13, 2014 12:39 pm
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Retroverbial wrote:
shimmilou wrote:
You should probably replace the one on each output tube, and use 2 watt replacements.


Do not over-spec them.

They're there to protect the amp in the event of a runaway tube.

Arjay


Not this again! :lol:

They are not meant to open and protect the amp, they protect the tube by keeping the screen voltage lower than the Plate voltage so that the screen doesn't become a defacto Plate. Fusible links (fusible resistors) are used in circuits when the component is supposed to open to protect the components, or even a fuse, but never a regular resistor. Many modern amps do use fuses to protect the circuit in case of a tube failure.

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Post subject: Re: fender twin reverb 1965 reissue problem update with pic
Posted: Mon Jan 13, 2014 1:02 pm
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simus35 wrote:
...do you think this they cause the spark boom sound when I play low freq. note. do you think I will need to buy a new set of tube too :?


Usually when a screen grid resistor burns, it means that the tube is shot and should be replaced. Replace output tubes as a matched pair.

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Post subject: Re: fender twin reverb 1965 reissue problem update with pic
Posted: Mon Jan 13, 2014 1:08 pm
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" They are not meant to open and protect the amp, they protect the tube by keeping the screen voltage lower than the Plate voltage so that the screen doesn't become a defacto Plate. Fusible links (fusible resistors) are used in circuits when the component is supposed to open to protect the components, or even a fuse, but never a regular resistor. Many modern amps do use fuses to protect the circuit in case of a tube failure. "

Correcto mundo! If anything, overspec helps protect the output tubes, during times of extreme transients. I like the 5-watt Mills ww resistors. They are small enough to keep the leads short. Yet, tough enough to work under extreme conditions.

Carbon comp in the grid stopper position is fine. I like flame-proof variety. Like Kiwame.

http://www.partsconnexion.com/resistors ... _watt.html


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Post subject: Re: fender twin reverb 1965 reissue problem update with pic
Posted: Mon Jan 13, 2014 2:16 pm
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+1 on the flame-proof resistors. Regular carbon film, or carbon comp resistors can actually catch fire. I would rather not have to deal with fire damage in an amp, or the possibility of something near the amp burning.

Compare this to the OP pic of the open flame proof resistors, big difference.

Image

That won't happen again.

Image

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Post subject: Re: fender twin reverb 1965 reissue problem update with pic
Posted: Wed Jan 15, 2014 1:04 pm
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shimmilou wrote:
simus35 wrote:
...do you think this they cause the spark boom sound when I play low freq. note. do you think I will need to buy a new set of tube too :?


Usually when a screen grid resistor burns, it means that the tube is shot and should be replaced. Replace output tubes as a matched pair.


but when a tube is shot, (the hot plate suppose to glow or not). ask them because someone told me that and he told me to look at the tube and if after 10 min if the hot plate not glow your tube is ok .
I hope you understand what I mean
thanks


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Post subject: Re: fender twin reverb 1965 reissue problem update with pic
Posted: Wed Jan 15, 2014 3:08 pm
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If you are referring to "red-plating", that only means that the tube is drawing too much current. There are many ways in which a tube can be bad. When a screen grid resistor is open (burnt), this is an indication that the tube has shorted internally.

When a screen grid resistor is open like yours, the tube is not drawing current, therefore could not red-plate. If you replace the resistor and use the same tube, likely the new resistor will open also. It might, or might not happen immediately, but it will happen.

A resistor will not burn open when there is no problem, so in all likelihood, the tube is bad and should be replaced.

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Post subject: Re: fender twin reverb 1965 reissue problem update with pic
Posted: Wed Jan 15, 2014 3:31 pm
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thanks for the info shimmilou


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