| Sjef |
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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| Sch3mat1c |
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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| Joel |
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.:nod: |
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| Sch3mat1c |
500k? Bah. Go look at my Rock Your World thread. (And they spec 50k maximum...harrumph :P )
Tim |
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| Joel |
| 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.:rolleyes: |
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| Sch3mat1c |
I still maintain that some wimpy 12AT7 pushing 150W of output doesn't feel right :)
Tim |
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| Joel |
| 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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| Sch3mat1c |
That theoretically I could use one but I didn't...
Tim |
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| fdegrove |
Hi,
| quote: | | That amp is a perfect candidate for some grid chokes then Tim. |
Well done Joel.You're spot on.:nod:
Cheers,;) |
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