300B, 2A3 experiances wanted

I apologize! It was Joe Roberts who was editor of Sound Practices. Joe Boyd was indeed a record producer. Blame it on my old brain which is not getting any younger!

I have had a 300B amplifier with a 6f6 driver for many years.

I upgraded and rebuilt it many times.

What was an essential upgrade is adding an interstage transformer between driver 300B instead of RC coupling.

My experience shows that monoblocks are not essential for good soundstage and imaging. It is enough to isolate right and left channel power supplies by LC or even by RC filter. It gives enough channel separation except sub bass that is not important for imaging. But sub bass isolation is super important for the driver to output power supply. Otherwise we get PS feedback between output and driver and as result motorboating that leads to loose bass. As a result, it is better to separate driver and output power supplies.

Another important subject is power supply capacitors quantity and quality. The same thing is important for cathode bypass capacitors.

Good point: the 300B driven by an interstage transformer is a completely different animal than a 300B driven by RC coupling. From that perspective, an IT is almost mandatory to hear the full potential of the 300B tube. By contrast, the 45 and 2A3 are much easier to drive, and RC coupling works a lot better.

(RC coupling typically throws away 1/3 of the power of the driver tube, while transformer coupling is about 95% efficient. Big difference.)

Great input @glennewdick  on your tube experiences, I will be saving it for reference. The interstage transformer idea is a new one to me. I will be looking for examples of that implementation down the road if I fall under the 300B spell, but I have to be honest and say the cost of 300Bs is a deterrent, so I am liking what I am hearing about the 2A3.

Can I pose a broader question to you gentlemen of experiance with tubes? When considering the difference among different brands of a given tube such as the 300B or the 2A3 or Even the EL-84 would one reasonably expect to hear sonic differences closer to changing one's speakers or one's cables? In other words is the design of the tube more controlling of the sound produced or is it the execution represented by particular brands or models within a brand?

I will chime in since you have already bought the piece of gear you are going to assemble.  I have 45’s, 2a3 and 300b amps-Triode Labs, 2a2, Yamamoto 45 and 300b and Coincident Frankenstein 300b and preferred the 2a3 over the 300b amps, better bass and treble and not far off a 300b on mids.  I used NOS RCA 2a3 and preferred them over any modern tube with better dynamics and better across the whole frequency band.  My favorite is the 45 but believe you can’t use that on your kit you will be assembling.   Congrats and good luck on the build!