I would suggest that you talk to Andy at Vintage Tube Services. He has been in the business (his only business) since the mid 80's and this has been an avocation for him virtually his whole life. His web page is www.vintagetubeservices.com or better yet call him at 616-454-3467.
His suggestions regarding replacing my 12AX7's from my Aronov preamp worked magic...much more musical and detailed. I also hate to burst your bubble but there are many grades of 6550's and what is currently out there is definitely substandard compared to the NOS Tungsols and Sylvanias. I should know. Andy put together some NOS Sylvanias and WOW!
At any rate it would definitely be to your benefit to call him.
His suggestions regarding replacing my 12AX7's from my Aronov preamp worked magic...much more musical and detailed. I also hate to burst your bubble but there are many grades of 6550's and what is currently out there is definitely substandard compared to the NOS Tungsols and Sylvanias. I should know. Andy put together some NOS Sylvanias and WOW!
At any rate it would definitely be to your benefit to call him.