Say a fella wants to build an SET monoblock based on the 300B..

I have built the Audio Note Kits DAC 4.1x and will be building the L5 Mentor preamp soon. These are top quality kits with good instructions and support. When I finished my DAC, even though the measurements were within the ranges specified, and it played flawlessly, I still sent the DAC to Peter Fulton to verify my work. I believe Peter is retired and I think he builds these kits more for the enjoyment than the money. Also, having done a lot of the builds he is probably very efficient which saves the customer time and money. In my shop, it would would cost significantly more than AN Kits mark up. It took me 8 hours to build the DAC, at our rates that is $1000, about 30% of the cost of the kit. So yeah, Audio Note Kits is offering a really good deal for the pre-built versions of the kits. It's almost a no brainer.

Does it have to be mono blocks? If not, the Elekit is fantastic. Especially with the Lundahl transformers. 

clio09,
The 4.1 DAC and Mentor preamp are gorgeous pieces that are truly drool worthy. If they were not out of my range, I would own both!

@roxy54,
What speakers were/are you using with the  Audio Note kit 330b SET?
Based on your earlier comments regarding your happy experience you obviously have a very compatible match.
Charles 

The Bottlehead Kaiju 300B amplifier was mentioned by another member. If you want to get into DIY tubes, the Bottlehead kits are a great way to go. The instructions are fabulously easy to understand and follow, and help is always available via a superb online forum. Most importantly, what you end up with is a high quality amp with excellent sonic performance. You get point-to-point wiring in the signal path, and the component quality is excellent. The Kaiju is a great 8 watt stereo amp that can be monoblocked into 16 watts per channel. I am currently running my Kaiju in stereo but hope to ultimately purchase another Kaiju kit to run as monoblocks.  I have also fallen in love with the DIY process. Building your own amps is great fun, and nothing beats listening to gear that you have built yourself. I can heartily recommend the Bottlehead kits in general, and the Kaiju 300B kit in particular.