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Old 28th September 2003, 05:44 PM   #21
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Hi,

Quote:
what value should the light bulb be 15w?
Or higher.

Cheers,
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Old 28th September 2003, 07:10 PM   #22
Raj1 is offline Raj1  United Kingdom
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Hi Frank,

well the circuit is virtually built, I didn't want to subject the 3a5's to this voltage incase they went lunar.........

The 170v at b+ with no load worried me, given that the max for the 3a5's is 135v, so I thought I'd ask before having to fork out for new tubes....

Do you think the tubes will be okay if i Just test the rail with them connected?


Incidentally I did use a light bulb across B+, it was a 60w 240v type, the voltage at B+ fell to 21 volts or so...?????

thanks
Raja
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Old 28th September 2003, 07:37 PM   #23
grataku is offline grataku  United States
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You may be overloading your PS. Be careful. Frank forgot to mention the wattage of the light bulb but you should know that a 60W light bulb is not equivalent to a 470kohm resistor.
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Old 28th September 2003, 07:41 PM   #24
Raj1 is offline Raj1  United Kingdom
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Don't worry won't be using the bulb again

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Raja
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Old 28th September 2003, 07:50 PM   #25
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Hi,

Quote:
The 170v at b+ with no load worried me, given that the max for the 3a5's is 135v, so I thought I'd ask before having to fork out for new tubes....
They won't melt if it's only for 30 secs but if you want to play it safe then up the value of R10 to 1K and work backwards using, you guessed it Ohms' law.

Or use a linear 1K pot of say 3-5 Watt and connect the wiper to the output.
Set it to 1K, let the circuit warm up, adjust for 110V...switch of and measure the resistance across the pot.
Replace the pot with the closest matching R.

Quote:
Frank forgot to mention the wattage of the light bulb but you should know that a 60W light bulb is not equivalent to a 470kohm resistor.
I can't remember the exact resistance but is pretty small indeed since it dropped the B+ from 170V to 20V...
Too lazy to do the maths...hey, it's Sunday.

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