amenity421

Sorry man. I should have actually answered your question. Watch this if you haven't yet: It explains it. Just ground to amp if it's missing the center pin (you'll know what I mean after you watch the video). Also, don't die.

Hey there, I just did my hd100 the other night. It's missing the center pin for ground so I just grounded to the amp. Make sure you have a speaker load connected. I biased mine at 40mv. Sounds nice and warm now. It had some tung sol 6L6s in it prior and I didn't much like the tone.