Your journey with lower-watt tube amps -- Can a kit be good enough?

A bit late to the party here, but it's a topic near and dear.  I've had Altec 604-8G in one of my systems for many years.  One day a friend and I did some trading, and I wound up with an Alan Eaton SE45 stereo amp.  It was quite pleasant and I enjoyed listening.  He had also brought over a 300B amp made by BEZ.  It was not impressive, very veiled, mushy, etc.  I kept the Eaton amp until I decided to make my own SE45 amp from vintage parts.  Output trannies are Triad HSM-79.  Borrowed and merged bits of circuit design from various sources, and the result was an amp that outperformed the Eaton amp, both on the bench (output at clipping and sq waveform) as well as sonically.  If you're wondering, I listen first, then measure.  I don't recommend scratch building unless you enjoy the journey, but the point of this comment is buy a kit with the best output transformers you can afford, as they are the heart of any single ended amplifier.  As for wattage concerns, 1.6 wpc does seem a bit lean, but if you're speakers are 95 db at 1 watt, they'll be 85 db at 1/10 watt.  Distance from speakers matters, room sound absorption matters, but unless you're looking for slam at disco levels, SE is a fun part of the audiophile journey.  Life is short, build the kit, savor the results.  I also have one of Dennis Had's KT88 Inspire amps, and it brings a little more punch, with up to 6x more wattage on tap.  All good fun.

The mention of a directly coupled cathode follower by atmasphere is interesting.  Today, I just happen to be looking at the schematic for an old Wyetech SET amp and noticed it had a directly coupled cathode follower to the grid of the output tube.  

Looking for stories about your low-watt amp journeys.

Using 100db Volti Rival for investigation tube sonics, chosen for its neutrality and affordability - I want to hear tube differences starting with flea at SET amplification.

Started with 300b because it’s the most notable SET. Purchased a used Coincedent Frankenstein 300b v2 because of its high performance/price sold directly.

Debating purchasing a TEKTRON TK TWO 2A3/50S-I VACUUM TUBE - 2a3, 45, 50, 300b - to investigate other flea watt SET tube types

Also debating DECWARE Model SE84UFO25 - long wait but great sonics and can tube roll

@alexberger 

The problem of 300B they need a driver with 150 volt peak to peak voltage swing. For 845 you need much more voltage swing.  

If you direct-couple with a CF that's no problem at all! Here's something to consider:

The grid of triode power tubes is the most capacitive of any kind of power tube. Triode power tubes are also very low mu (gain). For example the 300b is a bit over 2. The 6AS7Gs we drive in our OTLs is only 2.

So driving such a load from the plate of a driver tube is a task- hence the common use of an interstage transformer. But that part is expensive if its done right and it makes distortion and limits bandwidth.

When you use a cathode follower its input impedance is really high so its a lot easier to drive than a power tube and easier to drive than using an interstage transformer. So its a lot easier for the Voltage amplifier to drive it without distortion and the driver itself is inherently low distortion as well.

Since you are into DIY you might consider trying this. Its not that hard and like I said, the tube section to do it and the minus supply is usually less expensive than a good interstage transformer. As a general rule of thumb whatever the B+ Voltage is that you use now for the driver, if using a direct-coupled cathode follower you'll need a B- of equal absolute value. That will allow it to have the Voltage swing you need. A single 6SN7 section can easily swing 150V or more no worries. We've been doing it for decades. Usually you can obtain the negative supply if you use a bridge rectifier. That requires a power transformer with a center tapped secondary. 

I’m not a tube guy, but I am enjoying this thread a lot. Thanks @hilde45 for starting it, and thanks @atmasphere for your well thought out comments which, despite being nominally tube-oriented, hold a universal appeal especially regarding what we listen to, how we listen to it and what we seek to get from it.

My entire history with tube gear consists of a vague yearning for big-iron VTL monoblocks... someday... so I don’t have much to contribute to the subject other than, if you’re still considering the DIY route, this:

Unlike another poster earlier, I find PCB work easy. Insert component in its assigned spot, solder, done. Point to point on the other hand gives you a lot more latitude in how you structure your circuits in 3D space. Personally I find point to point more rewarding, but harder to keep my OCD impulses in check 😃

For what it’s worth, I would recommend going the DIY route, if only because the satisfaction of building something with your own hands is without peer.