Maybe Leaving SET for Solid State because I want bass

Your speakers are rated 60Hz -15,000Hz and 60 watts maximum.

Using tone controls to extend the LF response may damage the woofers in the long run if they are original from the 60’s.

As mentioned consider adding a sub or subs.

 

DeKay

Exactly, almost posted the same, at first thinking folks can hear and understand the difference in bass frequency gain with tone control is not the same as low frequency gain under 60hz with a quality subwoofer. Maybe not.     

Get a pair of REL T9/X Then keep the lovely qualities of your SET and get proper Bass properly integrated with you speakers. Well within your budget and huge bang for the buck

Why no one makes a modern high end preamp that has tone controls is beyond me.

@dhcod Its because the additional circuitry to do so colors the sound, even when the controls are set to flat. High end audio is all about getting as close the musical experience as possible; to hear exactly what is in the recording while being musically involving. 

@mswale makes a good comment about subs. To be effective with them however its of paramount importance that bass frequencies are not allowed into the SET.

The reason this is so is because most SETs have the current of the output tube flows directly through the output transformer. Since that current only flows in one direction, a DC magnetic field is created in the core of the transformer. 

This DC magnetic field saturates the transformer and so causes extreme distortion! To get around that problem, a tiny gap is introduced into the core of the output transformer. This pretty well kills the DC magnetic issue so the transformer can pass audio with low distortion, but it comes at a price.

The price is the inductance of the transformer (inductance is the electrical property that wire can have when wound in a coil as seen in transformers; it's the property that makes the transformer work) falls off at lower frequencies; the lower the frequency the more the wire behaves as if its not wound in a coil. 

When that happens, the output tube can't make the power its supposed to and its distortion skyrockets! So most SETs cannot play bass properly on this account, and bass causes them to make a lot of distortion if allowed into the amplifier.

So to get the most out of any SET, something must be done to prevent bass getting into it. Some subs have electronic crossover outputs that do this (as do subwoofer amplifiers should you choose to use a passive sub with your system). 

It is this very problem that caused Western Electric to seek alternatives back in the 1930s and the parafeed SET is one solution they produced. 

Obviously push-pull tube amps, solid state and class D amps do not have this problem. It is unique to traditional SETs. 

Anyone telling you their bass is perfectly fine with an SET simply has not heard what an amp without this problem can do.

I'm only the messenger here (don't shoot me). This problem with SETs was well understood prior to WW2; with SET re-introduction in the early 1990s people doing so simply were not versed in audio history; the problem was forgotten by most. But anyone designing output transformers for SETs is all too aware of this issue! That is why the output transformers for SETs are so large, so that they can try to get enough inductance at low frequencies despite the gap. 

But it doesn't work, since making the transformer larger causes high frequency problems and even so, such large output transformers still prevent the amp making full power at 20Hz.

By contrast, a Dynaco ST35 or SCA35 can make full power at 20Hz for a fraction of the price (IMO they sound better in the mids and highs too). And there are better amps out there than those. My personal opinion, but I think traditional SETs are a lost cause (which is to say this problem is not solvable); they got superseded for very good reasons. 

@atmasphere 

Really helpful write-up.  I guess the question is, does this apply to the OP’s specific SET, which is an Ayon putting out 30 wpc, which is highly unusual, apparently due to is use of 62B tubes.  I also apparently had lower distortion than typical of SETs, at least according to this review:

https://www.theabsolutesound.com/articles/ayon-audio-crossfire-iii-pa-power-amplifier/#:~:text=What%20the%20Crossfire%20III%20PA,find%20counterbalances%20an%20SET's%20drawbacks.

@dhcod Part of this is the fault of a vintage preamp I put in the system for a few weeks. The tone controls showed just how much bass the speakers were capable of, even if the rest of the sound was less than ideal. 

I'd argue the opposite about the type of bass you are hearing right now as-is. Turning up onboard tone controls makes for a weird type of flabby bass too. I'd bet on a much higher quality preamp [with no tone controls] paired with two smaller / fast subs would give you a type and quality bass (and resulting upper and mid frequencies) you've never heard before in this system, imo. Just Sayin'. :)