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In Reply to: RE: Choke or CCS loaded ECC83 in phono stage? posted by Tube747 on February 05, 2025 at 01:55:02
For a choke load, you're going to need at least 2000 henries; when Magnequest made one - I believe it was from a Freed design - it was rated >4000H at 1mA. They are now very hard to find.
But a choke will (approximately) double the plate voltage and current, which would call for adjusting the other resistors and capacitors. Plus, any choke not double-mumetal shielded against magnetic fields would likely pick up hum if used in the first stage.
The gain is set by the feedback network, not the stage gains, so current source loads would increase the feedback, not the gain.
The posted circuit appears to have voltages indicated, but the values are illegible so I can't offer much more. And the feedback network is partially cut off, so it's hard to guess the feedback-adjusted gain.
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"Still Working the Problem"
But it should be no problem to use CCS or plate choke for the line section circuit to replace the 270K and 100K, right?
http://www.pmillett.com/current_source.htm
Choke loads will have the same issues, more or less. CCS would be the way to go, in my opinion.
I'm recently working on very similar thing. Here's my friend suggestion.
" was talking about a resistor ACROSS the inductor! so the low DCR of the inductor will be used!!!
THAT shunting offers a real need, sets the impedance of the inductor to its value
Using a choke (inductor) as plate load and shunting it with a plate load resistor, will offer more plate voltage to the tube used. due to the plate load resistor will be the load impedance, not the DCR,
The choke will be maybe 50 ohms or so......"
Frankly, I don't know how to do that.
Is this approach okay 🙂
Paul,
After talking to my friend and he reminds me the CCS will make the linestage has too much of gain. And it required some change of feedback.
And he suggests I put a 400H plate choke with 3000 ohm DCR in series with, let's, say 267K resistor; so it ends up 270K for the plate load of the first ECC83.
And I can do the same thing to the second tube (same choke with 97K resistor).
What do you think?
If you are building a linestage, why use an ECC83 in the first place?
But it should be no problem to use CCS or plate choke for the line section circuit to replace the 270K and 100K, right?
http://www.pmillett.com/current_source.htm
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