Is it common for tubes to outweigh the cost of the amp or preamp?

George
that is ridiculously "high" pricing at your link 

https://www.newsensor.com/ProductSearchResult.aspx?Srch=kt88

Viva tubes 

https://www.vivatubes.com/search.php?search_query=kt88&section=product

I don't know how a tube headphone amplifier can be made for only $599.00... so with a cost that low, it stands to reason that some nice NOS tubes might well be more expensive. Normally not the case though.

As fate would have it that’s exactly how much I paid for my Woo Audio Class A all tube headphone amplifier about 5 years ago. Very classy, a sweet sounding amp and perfectly capable of driving my Sennheiser 600s. I used twin Sylvania 6SN7 Badboys and one WWII Tung Sol rectifier, total cost for tubes $300. I used two (count em!) Herbies Tube Dampers per tube, one on glass, the other on the base. Total cost for Herbies Dampers $300.

I appreciate all the feedback :)

I will chime in after work on the replies.

FYI the amp is a Woo Audio WA3. I've been using a Centrance Hifi-M8 for years with my HD800's and I've loved it. It was only recently when I picked up HD820's and plugged into my friends Bottlehead Crack that I realized I've been depriving myself. The OTL with those cans sounds so nice. Since I'm too lazy to build a kit amp I decided to go with the WA3 since it was similarly spec'd. I'm very impressed given the price.

And then... I googled "tube rolling". Whoops. So yeah, I got caught up in the hype. But if it's not hype and I do get a noticeable improvement then I'll be happy.

Thanks for the dialogue, folks!

300B tubes can often exceed the cost of the amp.