# Does the method for loading the plate affect gain of the stage?

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#### drlazybones

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.

#### DF96

Is the mu of the tube the maximum theoretical voltage gain regardless of loading method?
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.

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