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

I built an Elekit 300B SET amp with tons of upgrades (e.g. Mudorf caps, Takman resistors, Lundhaul power supplies and output transformers, etc.).  I love the amp but I wanted to increase power from 8w a side to 16-25 while staying in the SET camp.  I'm just starting the process of brainstorming. I was thinking of 300B monoblocks,
845 tube integrated or similar.  I want to stay under $5k and would need to sell some stuff--I have a wonderful Primaluna HP integrated with a good chunk of tubes to sell if I did this. I love that amp too but I don't need the power with horn loudspeakers and found the 300B a better match.  

Here are some off the head thoughts:
Manley 300B monoblocks (have to be used to make budget)
Line Magnetic 
Bottlehead 300B monoblock kit

I can do an integrated (but if it's an integrated I prefer a remote) or standalone amps and run them with a Schitt Freya I have for now.  Any advice will be appreciated in my research!  


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.

Yes- I get what the allure of the SET is all about. That inner detail they are known for comes out of the fact that as power levels are reduced, the distortion decreases to unmeasurable. When the distortion is gone, detail is revealed. There aren't many push-pull amps for which that is the case, but there are a few.

The problem is that you can't get much bigger than the 300b; people have built SETs with dual 300bs that aren't too bad but they are only 3dB more powerful (which is to say, twice the power); the problem is that the way the ear hears, 3dB just isn't that much louder. If you really want to play things louder you need at minimum 6dB more power, which is 4x more power than you have now.  A 30 watt push pull amp that sounds nice isn't that hard to find, but an SET with that sort of power is challenging.

Its that, get more efficient speakers, or live with what you have....

It may come down to living with what I have. At lower volumes the 300b SET is lovely. 

I’m curious to hear this as it is 4x my current output but still SET.  I’m not familiar with the power tube though. Drivers look to be 300bs though.

@jbhiller I'd love to hear how that sounds in comparison if you ever take the plunge... Hope someone else weighs in too.

I'm going to hear several of the Line Magnetic products Monday morning.  I have to hear them 250 miles from home so I can't bring my loudspeakers but I will put them through the paces and check back in. 
Love to hear what that 805 sounds like. There used be a guy building amps with SMPS and GM70 tubes with thoriated tungsten/mercury rectifiers. Sounded awesome even on YouTube.
As a point of information, while I’m not totally certain I believe the LM-805ia is the same amp as the LM-508ia that Shkong78 suggested earlier, and that is owned by at least one other highly respected member here, namely Waltersalas. Perhaps the designation that is used depends on the country the amp is supplied to, or the AC voltage it is set up to operate with.

Best of luck, JB. Regards,
-- Al
@almarg Interesting Al!  I may ping Mr. Waltersals!
Most of the 300B amps I've heard are low power vs. push pull, but still intended to mate with dynamic speakers, not horns. VAC Renaissance 30/30 is a particularly nice one. I've owned 845 amps from Dehavilland and listened to plenty of 211s, GM70s and similar. Most of those capture very similar magic to 300Bs, but their main advantage is the ability to drive more dynamic speakers that need the extra power, clearly not an issue here. Those SETs are great matches with 90-95db dynamic speakers but not so sure about with your horns. 
Not my area of experience, but have you listened to 2A3 or similar flea powered amps? Those are often paired with horns at 99db & up. Cheers,
Art Audio Jota?  I've just started using mine with a pair of 96db horn speakers and the experience so far is extremely good. I've been using the Jota for about 4 yrs now with upgraded tubes and I think it's marvelous. other things have come and gone but the Jota is a rock. If you can find one used they should cost around 4k, depending on tube set, condition, etc. The High Current version of the Jota puts out 24w per channel according to specs. Loudness has never been a problem, though that depends of course on the gain you have upstream of the amp. I've used the Jota mainly with Devore Silverbacks until recently, when I moved and switched to horns to accommodate a small(ish) listening room.  I might try another amp with the new speakers but mainly out of curiosity, not need. 

btw what are your speakers?  
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jbhiller OP417 posts02-08-2019 4:05pmWhat do you folks think of this option?

The Schitt Freya has two single ended RCA line level output pairs, which sends the same output signal to two sets of RCS. I could just build a second 300B and send left and right signals to each amp, then use one amp to power the high level inputs of my loudspeakers and one to power the low end.  

I forget the technical term for this mode of bi-amping. It's not monoblock style but rather using one amp to power both left and right high level speaker inputs and another for the lows. Thoughts?

I'm sure Atmasphere or others who could do the math could explain the effect on power. What seems like must be true is that I'd have more power and could stay outside of the distortion window of the 300Bs.  

What you are describing is referred to as passive horizontal biamping, JB. "Passive" because an active crossover is not being used to separate high and low frequencies "ahead" of the amps (the passive crossovers in the speakers doing that instead), and "horizontal" because each amp powers part of both the left and right speakers.

It is generally believed that when passive biamping is done with identical amps it is preferable to connect them in a vertical configuration, rather than in a horizontal configuration. Meaning that each amp is assigned to one speaker, with one channel of a given amp powering the highs of its assigned speaker, and the other channel powering the lows of that speaker. That way the two channels of each amp are processing the same signal, which eliminates the possibility that sonics may be adversely affected by inter-channel "crosstalk" within each amp. Also, it makes it possible to have shorter speaker cables, potentially minimizing the sonic effects of those cables.

That said, I’m not sure that biamping two of the 300B amps would make all that much of a difference in terms of allowing each amp to operate within its region of lowest distortion. While passive biamping reduces the amount of current and power each amp must supply, without an electronic crossover "ahead" of the amps they both would still have to output voltages corresponding to the full frequency range of the signal. And in any event the increase in the total amount of power that can be provided to the speakers would at most be only 3 db (i.e., twice as much). And the actual increase that is realized would be less than that much of the time, depending on the frequency content of the music and the crossover point of the speakers.

Finally, keep in mind that the preamp’s output circuit would see a load impedance corresponding to the input impedance of the amp divided by 2, since the two RCA outputs of the Freya are almost certainly driven by the same output circuit. It appears that your amp has an input impedance of 50K, so the Freya would see 25K when driving two amp channels. Looking at the specs for the Freya I would think that would be ok in the JFET or tube mode, but might not be optimal in its passive mode.

-- Al
I built the same amp about 1.5 yrs ago.  Pink resistors, SGO boutique coupling caps etc. It is a great sounding amp. 
I drive Heresy 3s with it in my bedroom.
What might interest you is PSE mono block.  I have a pair being built at this time.  I expect to get at least 20W (pentode) depending on my rectifier/output tube setup.  Paralleled Single Ended utilizing two output pentodes not 300B. They could be strapped triode or not.  Will put you right there in the ballpark.

+1 on the ANK Interstage Monos!  Also agree with looking for a higher efficient speaker to match a lower watt 300b.
Check these horns out:
@oldtech0,  who is building those Parallel Single Ended amps for you?  I'd love to check them out.
Seriously, if you want to continue using SET amps, consider a more efficient speaker. You'll get a lot more mileage for your dollar.
Dennis Had.  You can find him on the bay.  Just search for him.
@jbhiller Any updates on your audition of the LM amps?
I've read abut the Elekit amp and am thinking of it or the Bottlehead Kaiju as a next kit option. How was the build experience? I've built several kits and have had good experiences with all including a Bottlehead Smash preamp. 99dB sounds like pretty efficient speakers already. I use Pass Labs DIY Amp Camp Monos at 5 watts per side with my 99dB Klipsch Forte II's The 5 watt amps seem to have plenty of power in this setup. 
Advise you look for used Wavelength Cardinal or Art Audio Jota
Building the Elekit was not a huge ordeal.  Instructions are drilled down so even a less experienced person could get it done.
V.K. is a pleasure to deal with.  Man has a passion for DIY.

@cal3713   I took sick the day before my appointment to hear the LM stuff.  I have to reschedule it because I have to drive 4 hours to hear them--even though I'm in the third largest city in the US.