Did you measure these bias voltages or compute them?
Estimatings max cathode current?
- Thread starter kiira
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kiira
Well-known member
LOL ok showing work and i think I have it right this time
Ia = B+ - Va / Rl = 290V - 130V / 13K = 12 ma
For 100 ohm cathode resistor:
Vk = Rk * Ia = .1K * 12ma = 1.2V bias
for 1K cathode resistor:
Vk = Rk * Ia = 1k * 12 ma = 12V bias
So I see why the tube would bias with the 100 ohm resistor but it would not be at a good operating point.
thanks all
Kiira
Ia = B+ - Va / Rl = 290V - 130V / 13K = 12 ma
For 100 ohm cathode resistor:
Vk = Rk * Ia = .1K * 12ma = 1.2V bias
for 1K cathode resistor:
Vk = Rk * Ia = 1k * 12 ma = 12V bias
So I see why the tube would bias with the 100 ohm resistor but it would not be at a good operating point.
thanks all
Kiira
> I'd like to eventually make this a line stage that could drive 600 ohm inputs or phones without needing a xformer.
Why? That's like asking a greyhound to pull a sled. Some jobs are more suited to a mastiff.
Certainly whatever sweetness Darling found in this tube, working at high impedance, will be lost (at least totally different) with a low-Z load. There are several tubes that would strain less with low-Z loads.
Sure, you can do it. Peak current will be about 18mA, barely enough for +20dBm or 100mW in 600Ω. Put in a transformer, you could do 10 times better, and at lower distortion.
Working almost to current-clipping in a low-Z load, you will get around 5% THD, instead of the 1%-2% THD you get working into a hi-Z load at reasonable currents.
> Not as a grounded cathode of course.
GC is always best for power gain. When you have power gain, you can trade-off for lower distortion, wider bandwidth, whatever.
One extreme tradeoff is cathode follower. Power output is unchanged from a GC stage with the same current and voltage, voltage gain is lower and distortion is lower by the same amount. Simple feedback, but the simplest voltage feedback possible.
Why? That's like asking a greyhound to pull a sled. Some jobs are more suited to a mastiff.
Certainly whatever sweetness Darling found in this tube, working at high impedance, will be lost (at least totally different) with a low-Z load. There are several tubes that would strain less with low-Z loads.
Sure, you can do it. Peak current will be about 18mA, barely enough for +20dBm or 100mW in 600Ω. Put in a transformer, you could do 10 times better, and at lower distortion.
Working almost to current-clipping in a low-Z load, you will get around 5% THD, instead of the 1%-2% THD you get working into a hi-Z load at reasonable currents.
> Not as a grounded cathode of course.
GC is always best for power gain. When you have power gain, you can trade-off for lower distortion, wider bandwidth, whatever.
One extreme tradeoff is cathode follower. Power output is unchanged from a GC stage with the same current and voltage, voltage gain is lower and distortion is lower by the same amount. Simple feedback, but the simplest voltage feedback possible.
