59 Bassman Screen-Grid Resistor Burn

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pops
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Re: 59 Bassman Screen-Grid Resistor Burn

Post by pops »

If you need to drop voltage you can always mount a large choke before the first filter cap, it will have to be able to handle the power tube current so larger than usually used, i forget, but maybe 300ma if my old brain is remembering correctly. It will lower your voltages very nicely.
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Bourgeois
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Question on Resistor Wattage

Post by Bourgeois »

Hi, I have ordered 1 Watt 470 resistor from Mojotone for my screen-grid, and here is the resistor I have received (in blue). It is smaller in size compared to the original (gray). Are those wrong wattage? May I used them safely or re-order correct ones? I really do have trouble finding them online...

Thanks
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xtian
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Re: Question on Resistor Wattage

Post by xtian »

Bourgeois wrote:Hi, I have ordered 1 Watt 470 resistor from Mojotone for my screen-grid, and here is the resistor I have received (in blue). It is smaller in size compared to the original (gray). Are those wrong wattage? May I used them safely or re-order correct ones? I really do have trouble finding them online...
The blue ones are 1 watt, and OK to use. Different resistor compositions allow for different size/watt ratio.
I build and repair tube amps. http://amps.monkeymatic.com
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Jana
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Re: 59 Bassman Screen-Grid Resistor Burn

Post by Jana »

1 watt is a bit small to be using it as a screen grid resistor.
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rdjones
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Re: Question on Resistor Wattage

Post by rdjones »

xtian wrote:
Bourgeois wrote:Hi, I have ordered 1 Watt 470 resistor from Mojotone for my screen-grid, and here is the resistor I have received (in blue). It is smaller in size compared to the original (gray). Are those wrong wattage? May I used them safely or re-order correct ones? I really do have trouble finding them online...
The blue ones are 1 watt, and OK to use. Different resistor compositions allow for different size/watt ratio.
Question - is there any correlation between the color of the resistor body and the composition type ?
I ask because several batches of metal film resistors I have are all blue body color.
Others that are either unknown composition or carbon film are grey or tan color.
Just curious.

reddog
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cbass
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Re: 59 Bassman Screen-Grid Resistor Burn

Post by cbass »

Is the color on the outside Of fim resistors just an insulated coating?
I don't know if there is an industry color code though
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Bourgeois
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Location: Istanbul, Turkey

Re: 59 Bassman Screen-Grid Resistor Burn

Post by Bourgeois »

I have replaced the screen-grid resistors where one of them was visibly fried. I have also replaced the fuse. Powered-on the amp and nothing! even hiss :( The lamp is also not lit.

Should I start troubleshooting from the PT to make sure we have power throughout the circuit?

And could the short in the output valve causing grid resistors to burn can also damage the rectifier tube? I took it out and gently shook it and I've heard this loose wire noise...

Thanks
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