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Old 22nd January 2003, 04:56 PM   #1
Joel is offline Joel  United States
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Thumbs up good sound with cheapo chokes

Of course I couldn't leave it alone, so I made these changes to my three-quarter watt amp...
All the 150 Henry chokes are hammond 156C's for $10 each!
It sounds so good, I wonder why all other grid and plate chokes cost so much.
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Old 22nd January 2003, 06:29 PM   #2
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Default Interesting!

Hi Joel,

Do these chokes smooth the power?

How did it improve the sound?

Rick
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Old 22nd January 2003, 06:37 PM   #3
Joel is offline Joel  United States
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Hi Rick,

No, they are plate loads for the voltage amplifiers. The 3rd choke is in the place of Rg for the output tube.

So far I have noticed a slight gain increase and clearer highs over the 36k resistors I used to have there.

Makes sense since, for any frequency greater than 38Hz, I would have increased impedence over the stock RC stage.
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Old 22nd January 2003, 06:47 PM   #4
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So to replace the load resistors you calculate the inductive reactance (impedance) equivalent to the resistance and replace with a choke?

Must you choose a frequency (or range or range of frequencies) for this calc?

Thanks for bearing with me on elementary questions,
Rick
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Old 22nd January 2003, 06:55 PM   #5
Joel is offline Joel  United States
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Rick, the problem is always going to be the bass response. So, you want to have enough inductance to maintain adequate gain at low frequencies.
Using 2*Pi*F*L=impedence, you get 18k ohms for my circuit at 20Hz... which is just fine. The plate resistance of the 01A is 10k ohms, so a load of 10k would be the -3dB point.
You can see why, when using inductors, lower plate resistance tubes have better peformance. Although with a big enough choke, it doesn't matter.
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Old 22nd January 2003, 07:24 PM   #6
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Default WALKING THE TIGHT ROPE.

Hi,

Just as with OPTs,using chokes as anode load is a matter of balancing Henry in a quest of having sufficient bandwidth at the frequency extremes.

A lot of inductance will hopefully give good frequency response at the bottom and depending on the quality of the choke may compromise high frequency response to some extend.

It ain't simple,
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Old 22nd January 2003, 07:32 PM   #7
Joel is offline Joel  United States
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Default Re: WALKING THE TIGHT ROPE.

Quote:
Originally posted by fdegrove
It ain't simple,
It isn't that hard either.
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Old 22nd January 2003, 07:58 PM   #8
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Default Re:It isn't that hard either.

Hi,

Quote:
It isn't that hard either.
Wouldn't that depend on the goals you set?

Cheers,
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Old 22nd January 2003, 08:07 PM   #9
Joel is offline Joel  United States
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It's a coil of wire! what "goals" do I have to set??
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Old 22nd January 2003, 08:32 PM   #10
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Default WHAT GOALS?

Hi,

Bandwidth for starters,that's what.

Cheers,
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