Preamp Recommendation for First Watt F4

I am planning on building a First Watt F4 because it would be a good learning experience and, by all accounts, it's a great amp in the right system. Can anyone provide specific recommendations for the companion preamp? My guidelines are single ended, 20+db gain, and preferably tubes. Not ideologically opposed to solid-state, but think tubes are better fit in general. My short list:
CJ ET7s2
Aric Mother Load II
Allnic L7000


Many folks are reporting excellent results with the Pass B1 with Korg triode.

I'm currently building one for my F5 amp and to try with other stereos. I'm adding film coupling caps and an external linear power supply but otherwise stock. If I really like it, I'll add remote control volume later.

The first link is for the kit ($299 complete). The second is a lengthy build thread.

It would be interesting to see how much better the line stages the OP lists are than this inexpensive kit when built with decent film coupling caps. The stock electrolytics are 10uf. Recommended film values to keep size down are 0.22uF for the first cap in the signal path, 1uF for the second and around 3.3uF for the output.

B1 with Korg Triode (B1K) Full Kit

B1 with Korg Triode Build Thread

Not as many as I would like.  The F4 was the first piece of equipment I bought when I was assembling my new system.  I heard so many great things about it and it was very inexpensive by high-end standards.  I ended up purchasing a Pass DIY BA-3 to accompany it because it was also reputed to be very good for the money.  The combination sounds great, just not enough gain & watts for most systems.  I purchased a pair of Graham LS 5/5 speakers because I listen to a lot of classical music and they match my sonic priorities very well.  So I purchased a more powerful amplifier and ended up using the volume control on my Meitner MA3 DAC rather than a preamp.  So many possible combinations and only so much money for hi-fi equipment.

I would love to be able to hear the F4 with a very nice high gain preamp, and expect it would sound great.  I think it would also be enough juice for 80% of my listening.  I plan on keeping the F4 indefinitely even though I'm not using it now.  If I were looking for a good inexpensive matching preamplifier, I would strongly consider a (used of course) Blue Circle BC 3000.  Lots of gain and I liked it very much.  I had one couple of decades ago and thought it was much better than the Hovland HP 100 that all the critics were falling over at the time.  I sold the Blue Circle to purchase the  Hovland and that was my way of truly learning that critics are just other people's opinions and what counts is mine.  I would also consider a CAT from Ken Stevens.

@vinylvalet :
The Pass B1 and F4 are mirror images.  Both presume that there's plenty of gain in your system and simple is better.  One solves the problem on the amplifier side and the other on the preamplifier side.  Also heard lots of good things about the B1 and have considered picking one up used, but am trying not to become a hoarder.

I was referring to the more recent Pass Korg B1, much better than the original Pass B1.

I would build the basic kit without mods before investing in an expensive tube line stage. Careful with used units since the Korg Nutube 6P1 is very microphonic which will cause problems if not mounted properly. This inexpensive kit will improve that considerably:

Anti-vibration Mount for Korg Nutube 6P1

I'm guessing mine with mods and external linear supply will hold up well to both my main tube lines stages, both above $10k, especially since I will be able to dial up any amount of second harmonic distortion by simply adjusting the bias pots.

I am using an Usher P307A with my rawsonte F4. Possibly the best amp/pre combo I ever had ( with Lascalas ). Enjoy ! MrD.

My guidelines are single ended, 20+db gain, and preferably tubes. Not ideologically opposed to solid-state, but think tubes are better fit in general. My short list:

This is a proven alternative to drive the F4 cleanly to rated output. ra7 said he will may have an updated version available later this year.