After some listening I am very happy with the purchase. From minute one, before any warming up or burning in, I noticed a significant improvement.
The new tubes have added so much detail to the highs and tightened up the low end which is resulting in a much bigger soundstage. They've given my HD820's a soundstage more comparable to how my HD800's were sounding with the stock tubes while still retaining the more full sound of the 820's. I'm also not experiencing the listening fatigue with my 820's like how I was with the stock tubes. I can listen to them for hours without a break now like I could before with my 800's.
Were they worth $640? For me, yes, and here's why. They are rated to last up to 15k hours so that comes to $0.04 per hour of listening. My turntable cartridge cost me $600 and is rated to last up to 2k hours which comes to $0.30 per hour of listening. So even if the tubes died after 2133 hours, that'd come to the same $0.30 per hour cost as my turntable cartridge. It was totally worth it for the improvement in sound I got when upgrading my cartridge. The improvement in sound from the upgraded tubes is just as significant and much cheaper when it comes to dollar per hour value.
I look at tubes in the same light as my turntable cartridge. Better cartridges/tubes equate to better sound, and both wear out and need replacing so you're essentially paying by the hour with stuff like that. Considering it comes out to pennies on the dollar, I'd rather have a superior listening experience than pinch pennies and get subpar sound.
