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Old 18th January 2007, 09:48 PM   #1
nhuwar is offline nhuwar  United States
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Default Bias resistor

Ok i know it's a good idea to put a bypass cap in parallel with resistor to adjust the individual grid bias on each tube

But what is a good cap value???
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Old 18th January 2007, 10:37 PM   #2
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You really should buy the Morgan Jones book. It explains how to figure this out in gory detail. The short answer is, large enough such that the frequencies above about 2Hz are not rolled off.
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Old 18th January 2007, 10:40 PM   #3
nhuwar is offline nhuwar  United States
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Ok so just simple cap reactance formula

Just wanted to make sure audio seams to be such a diffrent animal then rf some times I figuared id ask.

Thanks
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Old 18th January 2007, 10:41 PM   #4
nhuwar is offline nhuwar  United States
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Oh whats the title of the book?

Nick
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Old 18th January 2007, 10:50 PM   #5
nhuwar is offline nhuwar  United States
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Wow it's a pricey book for a paperback $46.76
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Old 18th January 2007, 11:03 PM   #6
Sherman is offline Sherman  United States
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Quote:
Originally posted by nhuwar
Wow it's a pricey book for a paperback $46.76

And worth every penny!



This formula will give you the value of the bypass cap in microfarads.

1/(2pi*f*i)*1000000

Where 'f' is the desired -3dB frequency and 'i' is total impedance computed as

i = (rp of tube * plate resistor)/(mu of tube +1)
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Old 18th January 2007, 11:06 PM   #7
SY is offline SY  United States
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Quote:
Originally posted by nhuwar
Wow it's a pricey book for a paperback $46.76
A 600+ page paperback.

It quickly became the most-used book on my tube electronics shelf. Truly worth it, trust me- it will save you from enough dumb mistakes to pay for itself in no time.
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Old 18th January 2007, 11:28 PM   #8
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Sy,
Which of his books are you referring to? Thanks, Victoria
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Old 18th January 2007, 11:47 PM   #9
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Hi all ,

ď Valve Amplifiers by Morgan Jones ď
Great , fantastic , well written , easy to understand and
very didactic , too .

I bought mine , due to many advises from SY , on this
forum , and the book really worth every cent of dollar .

Hi nhuwar ,

I donít know why you are speaking about USD$ 46.76 ,
because I paid USD$ 49.94 ( book + shipping ) delivered
at my door ( Sao Paulo , BRAZIL ) from Amazon.com ,
5 months ago . Inside USA , the price must lower !!!??

Carlos
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Old 18th January 2007, 11:55 PM   #10
SY is offline SY  United States
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No, it's not really any cheaper here.

Victoria, yes, "Valve Amplifiers," Morgan Jones, 3rd Edition. Jones has a rare knack for explaining- I wish he'd do a few more books.
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