Recommendations on stuff to look at for upgrading a 300B SET amp

https://forums.stevehoffman.tv/threads/new-line-magnetic-508ia-integrated-amp.542333/

I am happy with LM508 after tube rolling.

@jbhiller

What you are up against is that to make more power, SETs have to sacrifice bandwidth. 300b amps are at about the limit of what can be considered 'hifi'; even then its very difficult to get them to go from 20Hz to 20KHz and most of them don't.

Because a horn system is about the only thing that has enough efficiency (or in some cases, single driver full range speakers like Lowther) to work with a 300b, this isn't too much of a problem because most horns and full range drivers can't make much bass below 40-60 Hz anyway.

Now of course you will hear of a lot of people running speakers that are less than the sort of efficiency you need (+99dB) but they really aren't getting the best performance out of their amps as a result unless they are listening in a smaller room. To really take advantage of what SETs bring to the table, you really don't want to push them past about 20% or so of full power, otherwise they start sounding 'dynamic' but this is entirely caused by distortion. BTW, once you know this fact, its easier to hear that such is the case so I may have ruined it for you- if so, my apologies.


The ear uses higher ordered harmonics to sense sound pressure, and SETs generate more higher ordered harmonic distortions once they start getting over about 20-25% of full power. Since music has lots of transients, as you turn up the power these harmonics initially are showing up on the transients of the music- and that is how they sound more 'dynamic' than one would expect for a lower powered amp.


If you really need more power (if a more efficient speaker is out of the question), IMO/IME you are far better off looking for a lower powered push-pull tube amplifier. You'll hear more detail and bandwidth won't be a problem. Most such amps won't be as lush since they don't make as much 2nd order harmonic distortion, but overall they stand a chance of being more musical than a larger SET.

So, how about changing your speakers to something more efficient? Or, looking at other tubes like GM70 or 211?Check out Lampizator and NAT.

@atmasphere , I know you to be super knowledgeable and I really appreciate what you are saying--so much so that it’s making me rethink the tube world, even if just for today. My speakers are 99dB efficient by specs. Maybe I’m just better off staying put.

I loved the push pull Primaluna with my PSB T2s (89dB) but I ventured into the 300B world and loved its intoxicating recreation of vocals. Maybe the solution is just to run two systems?

I almost know you have to be right about the 20-25% rule just by what I hear, which is nothing compared to your experience level as a builder of fine amps.