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Old 29th January 2003, 08:50 PM   #1
Sjef is offline Sjef  Netherlands
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Default grid chokes

Has anyone any experience with the use of grid chokes instead of grid resistors in a 300B amp ?

I was wondering what the sonic benefits are.
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Old 29th January 2003, 10:54 PM   #2
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Default grid choke

I did one with the well known Opera Billie 300b.
http://groups.yahoo.com/group/doctor...500%206S45.gif

very worthwhile
I imagine mileage will vary w/ circuit, no?

I Don't have any other experience with grid chokes.

I'd go for it.


Craig Ryder
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Old 30th January 2003, 02:08 AM   #3
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I see no advantage to it unless you're drawing grid current and want to keep the DC level exactly where you want it, but to each his own I guess...

Tim
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Old 30th January 2003, 02:06 PM   #4
Joel is offline Joel  United States
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Tim, there are actually some benefits to using a grid choke. All tubes have a fractional amount of leakage current in the "grid circuit". The big old triodes have a bit more, and so you'll often see a limitation on grid DCR - and you'll see two numbers, one for self bias, and one for fixed - the value for fixed being a fifth lower usually. This is because in the self bias situation the tube can compensate for any change in it's grid-cathode voltage relationship, whereas in the fixed situation - it can't.
You might ask, what's the big deal? Well, even a small leakage across 1 meg can shift the bias enough to cause problems.

So.... we can use a choke between the grid and ground instead, and those teeny tiny currents will only see a few thousand ohms, instead of 500k, etc. Of course the AC signal sees the inductance of the choke as a high resistance, and away we go!
Make sense?

A Hammond 156C is a cheap $10 way to try them out for yourself.
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Old 30th January 2003, 03:05 PM   #5
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500k? Bah. Go look at my Rock Your World thread. (And they spec 50k maximum...harrumph :P )

Tim
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Old 30th January 2003, 03:17 PM   #6
Joel is offline Joel  United States
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Quote:
Originally posted by Sch3mat1c
500k? Bah. Go look at my Rock Your World thread.
A 22k Rg seems like a waste of perfectly good signal voltage to me.
That amp is a perfect candidate for some grid chokes then Tim.
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Old 30th January 2003, 03:21 PM   #7
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I still maintain that some wimpy 12AT7 pushing 150W of output doesn't feel right

Tim
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Old 30th January 2003, 03:26 PM   #8
Joel is offline Joel  United States
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Quote:
Originally posted by Sch3mat1c
I still maintain that some wimpy 12AT7 pushing 150W of output doesn't feel right
What are you referring to?
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Old 30th January 2003, 04:14 PM   #9
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That theoretically I could use one but I didn't...

Tim
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Old 31st January 2003, 12:31 AM   #10
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Default CHOKIES

Hi,

Quote:
That amp is a perfect candidate for some grid chokes then Tim.
Well done Joel.You're spot on.

Cheers,
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