Yes. In order to linearize the impedance, which, if these resistors were not there, would vary considerably with frequency, in particular when the inductance and parasitic capacitance resonate.Can somebody please explain the two 10k resistors at the output transformer primary? Are they there to load the transformer?
In othere words it's called damping.
It is necessary because the circuit does not use global NFB.
That's all normal and predictable. In pentode mode, the internal resistance of the tubes is very high, so the circuit is undamped. In triode mode, the internal resistance of the tubes is much lower, which provides the necessary damping.The aforementioned Rohde & Schwarz output transformer have a rather high dcr compared to the Lundahl. In my simulations, lowering these 10k resistors resulted in lower output but also flatter frequency response, especially the low end extended. With no resistors at all the low frequency response dropped considerably but only in pentode mode.
Your conclusions are correct.I’m also asking because I’m contemplating about where these transformers are better suited. Am I right in assuming that the high primary DCR makes them less ideal for push pull circuits? The older single ended circuits like BA-2A had output transformers with rather high dcr but all the push pull transformers I looked at have lower dcr. I suspect that the gap in the single ended transformers account for the higher dcr because it needs more windings to get similar inductance?