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In Reply to: RE: 417A linestage posted by dave slagle on January 22, 2016 at 13:35:07
Dave,
It might sounds crazy as we might parallel one more tube to the circuit and the outputz should be pretty low, around 600 ohm.
Also, we have 41 steps attenuator and it should be fine to deal with the gain of 40.
Thanks!
Follow Ups:
Hey,
you will get closet to a Z-out of 600R if you bypass the 80r cathode resistors but as it is drawn the apparent rp of the tube is = Rp+(Rk*(Mu+1) so assuming a mu of 43 you get an Rp of 5220. When you load that with 5K you get an output impedance of 2550 ohms, parallel two of those stages and you get an overall output Z of 1225.
Bypass the cathode Resistors and you get 5K||1.7K for 1270 ohms per tube and 635 for the parallel pair.
dave
Dave,
I'v3e seen people build with one single 417A in the circuit only with 4.8K plate load and 62R cathode resistors. And the result is wonderful.
I agree one single tube would be a magic piece without paralleling tubes as far as the load (input) impedance is high enough.
What do you think 300v B+ for 417A?
Regards,
Andy
Oh yeah.... to get back to your original question according to spice the tubes will draw about 20ma giving a bias of 1.6V and the gain will be in the ballpark of 26dB. Output Z is 1.275K @ 1Khz going up to 2.4K @ 20hzdave
Edits: 01/23/16
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