You see, the purpose of output transformers in amps like that is to present the tube driving them with an ideal load for that particular tube. So for example let's say the tube wants a 5k load on its plate. Well, in order to get that from a nominal 8 ohm loudspeaker load, the transformer has to be a step-down type with a 25:1 ratio. Transformers reflect impedances as the square of their turns ratio so with an 8 ohm load on the secondary, the tube will see 25^2 x 8, or 5,000 ohms. Now let's say you connect a 50 ohm headphone to the 8 ohm tap. Instead of seeing a 5k load on its plate, the tube will now see 25^2 x 50 or about 31,000 ohms. With the HE adapter connected to a 50 ohm headphone, the impedance on the secondary is 33 ohms so the tube will see a load of about 21,000 ohms.
Eliminate that series resistor and the secondary will see 10 ohms in parallel with 50 ohms, or about 8.3 ohms and now the tube will be loaded with something much closer to the 5k ohms it wants to see.
Thanks for your input, se. I had a feeling this match wasn't optimal and was being held back. Temptation has me wanting to send the adapter your way with a commish! Will knock on a few more doors explaining to those that answer "Here's what I need done..."
Lastly, if I'm going to making changes inside the box, is there any advantage to running the amp @ 8 Ohms or 16 Ohms for the HE-6?
Additionally, the little piggies are neat & tidy. No need for a new adapter or work done for the HPO.
Edited by Silent One - 11/25/13 at 7:50pm