1) Yes!
2) HT- is connected to ground via a 1K resistor and 25uF decoupling capacitor. This is probably to ensure the grid (pin 3) of the output valve is properly biased with respect to ground. (Should be a small negative voltage.)
3) Yes, but there is a blocking capacitor in series. Capacitors pass AC and block DC. There should be no DC component after the capacitor.
4) Yes. But always check with a voltmeter first! (you don't want to short the HT to ground because of a leaky capacitor!)
5) (Holding a wet finger in the air!) I would have thought that a few K should be OK, but you may need to experiment. The DL92 is regarded as a low output device, hence the need for a high impedance load. However, it was designed for portable radio use, so their definition of "low-output" may not tie in with ours!
Here is a sample circuit for a DL92, showing a speaker impedance of 8K for a quarter watt output, but it is DC coupled, so the speaker actually forms the anode load. Not a good idea, I would have thought, but cheap!
TRF receivers are notorious for marginal stability, and I'm guessing the strange connection between the HT- and ground is an attempt to improve this, as well as providing the necessary bias for the output device.
Best of luck!
--
Pete
