Help with resistor value.

[karma1967]

Hi,

My valve amp went distorted on Sunday, and one of the power valves started to glow redder than the rest.

I quickly turned it off and tried a spare set in. It still sounded distorted so today I had a look inside.

I can see a fried resistor, this is a good one, Would anyone care to tell me the value please?


https://i.imgur.com/1V5pXGE.jpeg


The fried one!


https://i.imgur.com/wez4giX.jpeg

[Jimbo]

Err the banding on the resistor looks kinda fried Jamie so difficult to tell what the resister value is?

[Firebottle]

The good one is 470 ohms, possibly a 1 Watt rating, could be 1/2 W.

Is it a screen grid resistor?

[karma1967]

Cheers Alan,
Its under the power valve,KT88. Is there an easy way to check? Also what watt should i go for?

[Barry]

Before you replace the 470 Ohm (1W) resistor, you should find out why the resistor burnt out, and in doing so, has damaged the adjacent wiring.

[Firebottle]

Cheers Alan,
Its under the power valve,KT88. Is there an easy way to check? Also what watt should i go for?

Does the good resistor go to the same pin on the other valve as the burnt out one?
Once replaced try a known good valve in that position, the original valve in that position could be suspect.

Go for a 1W, no harm in fitting a bigger size resistor.

With all the power off you could try measuring the resistor with a multimeter, it is likely fried to a higher value, that is the usual outcome.
Replace it anyway and also check the insulation on the wire underneath is undamaged, probably just charred a little looking at the picture.

[karma1967]

Will do, the resistor goes to pin 6 and 4 on all 4 Kt88's.
Cheers for your help.

[karma1967]

just to follow up, it was a blown signal valve that caused the resistor to fail. new valve and she's back to normal again.