|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
202.40.157.7
Hello!
Let's say I want to replace the plate load resistor with plate choke. Assume the plate resistor is 1.96K, should I have the DCR of the plate choke make for 1.96K?
Someone told me that a reactor is not same as resistor. A plate choke is a different impedance (reactance) at each frequency, increasing its value as frequency goes up.
Example:
A plate choke (reactor) to be 1960 ohms at 25hz, needs a 12.4H choke.
................................................at 1khz needs a .311H choke
................................................at 10khz needs a .03H choke.
Is that true??
Follow Ups:
1.) AC requirements
At the lowest frequency (for example 25Hz), you need -at least- four times greater load, than tube's output impedance. In this case it is 1960R.
If this "R loading" is correct, your tube's output impedance about 1/4 of load (Ri= 1960/4), about 500R.
At 25Hz the minimum required inductance is:
L=1960 /(2*pi*25) about 12.8H.
This inductance at higher frequencies generates higher value load, so distortion will be better there.
2.) DC requirements
Your "R loaded" tube DC operating point depends of cathode-grid voltage: Ua, Ia.
Sample Ua:150V Ia:20mA
The B+ voltage is larger, than Ua + required swing/2.
In this case the 1960R at 20mA 39.2V, so B+ =189.2V, half swing is 39.2V, the max swing is 78.4Vpp.
If you use plate choke, the B+ would be 150V+ (Ia*Rdcr).
At choke DCR -for example- 500R it's about 160V.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: