[ keith-snook.info ~ Un-bypassed Cathode Amplifier ]

~ Triode Amplifier Un–bypassed Cathode Calculator ~

This Calculator was originally made to support my Amplifier–Buffer project and can be used to calculate the a.c. gain and impedances [not d.c. operating point] of a any triode amplifier with a common cathode gain stage and a cathode follower output buffer so the overall gain is not significantly affected by the output load

The results update as new input variables are entered ~ g_m r_a and µ should be taken from the valve characteristics or manufacturers data ~ The default values are for an ECC81 with gain stage V₁ I_a ≈1mA and Cathode follower V₂ I_a ≈2.3mA ~ Calculated values r_a1' and g_m1' indicate how R_kaffects µ and g_m and may improve distortion

I have included an anode load R_L2 in the cathode follower stage so the effect of such can be seen or the output A_RL2 can be used to calculate the gain of a concertina phase splitter when R_L2 and R_K2 are the same value so the outputs are the same level but in anti–phase ~ Or just use the A_V1 value


Variables for gain stage —	V₁
Mutual conductance — g_m1		mA/V — See notes below
Internal anode resistance — r_a1		kΩ
Amplification factor — µ₁		Check — g_m1×r_a1 =
Anode load resistor — R_L1		kΩ
Cathode resistor — R_k1		kΩ
Calculated results for V₁ gain stage
r_a1 modified by R_k1 — r_a1'		kΩ = r_a1+ (µ₁+1) · R_k1
g_m1 modified by R_k1 — g_m1'		mA/V = µ₁/ ( r_a1+(µ₁+1) R_k1)
Unloaded voltage gain — A_V1		V/V = µ R_L1/ ( R_L1+ r_a1+ (µ₁+1) · R_k1)
Unloaded voltage gain — A_V1		dB = 20log (A_v1)
Output resistance at V₁ anode		kΩ = r_a1∥R_L
Variables for cathode follower —	V₂

Mutual conductance — g_m2		mA/V — See notes below
Internal anode resistance — r_a2		kΩ
Amplification factor — µ₂		Check — g_m2 × r_a2 =
Anode resistor — R_L2		kΩ
Cathode resistor — R_k2		kΩ
Calculated results for Cathode Follower V₂
Gain at V₂ anode — A_RL2		= µ₂ R_L2/ ( R_L2 + r_a2+ (µ₂+1 ) · R_k2)
Gain at V₂ cathode — A_Rk2		= µ₂ R_k2/ (R_L2+ r_a2+ (µ₂+1) · R_k2)
Output resistance at V₂cathode — R_out		Ω = (r_a2+R_L2) / (µ₂+1) ∥ R_k2
Overall voltage gain at V₂cathode		V/V dB = 20log (A_v1A_Rk2)

Keith Snook triode amplifier calculator

The value entered for g_m is not used to calculate results but is used to calculate the value µ = g_m × r_a which should be close to the entered value of µ for the results to be valid ~ As with most calculations with triodes g_m and g_m' could be used but r_a and r_a' would also be needed ~ The factor (µ+1) helps simplify things

It is assumed the d.c. bias is optimised for both the gain stage and follower and that the separate values for g_m r_a and µ have been found and entered for both stages and that a sensible I_a and HT voltage have been chosen

Click here for other calculators ~ ΐ

" I'll rise when the sun goes down ~ Cover every game in town "