I had a conrad-johnson PV-14L preamp. The best tubes were a little hard to find (Mullard M8080), but they lasted forever. I upgraded to a Premier 17LS2, but it developed an issue and I returned it.
I went to a LTA MicroZOTL preamp. It's not known be be overly warm sounding like the older c-j, so I was worried that I'd miss the warmth. Don't miss it at all. The LTA takes four tubes, but they last a long time. The NOS Telefunken tubes that I like are a little pricey, but there are NOS Siemens tubes that are a close second for less money.