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!  


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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.