I have a general design question about whether the chosen plate load makes a difference to the gain of a driver stage. Is the mu of the tube the maximum theoretical voltage gain regardless of loading method?
I would like to build a 2 stage single-ended all DHT amp with input sensitivity of 2Vpp. It doesn't appear to be possible without a relatively high gain driver, unless there is some secret plate loading method that can cause a tube to exceed its mu.
Here is a proposed output stage:
801A@520 volts, 35mA (18Watts max plate dissipation)
cathode biased at 37 volts using 1.1k resistor
plate loaded with 10k (or 11k if I can get a custom wind) SE OPT rated at 40mA with an 8 ohm secondary
I would like to use a single DHT driver, IT coupled. With a 2Vpp input it would need to swing +/- 37 V on the 801A grid. Please bear with me because I'm still learning, but I assume that I would need to use a tube with mu of (2*37V)/2Vpp = 37 in order to accomplish what I would like to do, unless there is a method of loading the driver tube that can somehow boost its gain. I want to ignore the possibility of using a step-up interstage transformer right now and just get some feedback from anyone out there who might be able to shed some light on this.
I've seen quite a few posts about using the 4p1l triode strapped as a driver, but I see its mu is only 11. What is the effect of using a CCS to load that tube versus a simple resistor or choke, for example? I'm sure it's capable of the voltage swing I want, but I don't think it has enough gain for a single stage.
I would like to build a 2 stage single-ended all DHT amp with input sensitivity of 2Vpp. It doesn't appear to be possible without a relatively high gain driver, unless there is some secret plate loading method that can cause a tube to exceed its mu.
Here is a proposed output stage:
801A@520 volts, 35mA (18Watts max plate dissipation)
cathode biased at 37 volts using 1.1k resistor
plate loaded with 10k (or 11k if I can get a custom wind) SE OPT rated at 40mA with an 8 ohm secondary
I would like to use a single DHT driver, IT coupled. With a 2Vpp input it would need to swing +/- 37 V on the 801A grid. Please bear with me because I'm still learning, but I assume that I would need to use a tube with mu of (2*37V)/2Vpp = 37 in order to accomplish what I would like to do, unless there is a method of loading the driver tube that can somehow boost its gain. I want to ignore the possibility of using a step-up interstage transformer right now and just get some feedback from anyone out there who might be able to shed some light on this.
I've seen quite a few posts about using the 4p1l triode strapped as a driver, but I see its mu is only 11. What is the effect of using a CCS to load that tube versus a simple resistor or choke, for example? I'm sure it's capable of the voltage swing I want, but I don't think it has enough gain for a single stage.
Yes, unless you use positive feedback - which is often a bad idea. A CCS or choke load will get you close to the maximum. A resistor load may get you 60-80%. Remember that the grid resistor of the next stage is, for AC purposes, in parallel with the anode load.Is the mu of the tube the maximum theoretical voltage gain regardless of loading method?
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