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In Reply to: RE: Can I use a resistor instead of the choke for coupling to the 813? posted by dave slagle on October 29, 2014 at 13:11:30
The choke between pin 2 of the 6em7 and opt. At least that is what I assumed it was since it says 10h. I guess couple was probably the wrong word to use; is it more part of the plate load?
Edits: 10/29/14Follow Ups:
That is a PS ripple reduction choke to decouple the output from the driver. Its goal is to provide a high AC impedance to ripple and low resistance to DC.
dave
And your suggestion for a resistor to replace it temporarily?
Dave, Great to have you back.
That 10Hy choke is between the B+ supply and the driver tube, not between the opt and the driver tube even though that's how it looks. The B+ supply is feeding both.
You could use a resistor in it's place but you would have more PS ripple on the plate of the driver cathode follower stage and the plate of the voltage amplifier stage.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Ok, I see. Thanks. My B+ is pretty clean, so I would like to give it a try until I can get my hands on the choke. How would I calculate the ohms/watts for the resistor?
I would use a 100 ohms resistor.
Calculate the total current draw though the resistor.
The voltage at pin 6 divided by 12k ohms would be the current draw of the input stage and the voltage at pin 3 divided by 3.2k ohms would be the current draw of the cathode follower stage.
If you add them together, that will be the total current through the 100 ohms resistor. You can figure out how much voltage drop there will be across the 100 ohms resistor. Current times resistance equals voltage.
Voltage times current is the power in watts (heat) that the 100 ohms resistor will have to dissipate.
BTW With a resistor instead of a choke I would use a larger value filter cap. Instead of 10uf I would go 100uf to try to keep the ripple down.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Thanks Tre'
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