Maybe Leaving SET for Solid State because I want bass

@mdalton The minimum frequency varies depending on the output transformer of the individual amp.

I repaired an SET recently that made 12 Watts. When I tested power bandwidth, I found that it hit a wall at 90Hz. Below that its maximum output power without excess distortion dropped; at 20Hz it could only make 1 Watt.

The bigger the output transformer relative to the output power, the lower it likely can go. Lundhal is known for making some excellent output transformers but even their best is unable to allow a 300b to make full power at 40Hz- its down a few watts.

So I'm saying you should measure it to find out. But in general if you cut off at about 80Hz (and use a subwoofer) you'll hear a marked improvement in the sound of any SET (that isn't a parafeed) - more relaxed, greater authority and detail. All that is needed to do that is a capacitor in series with the input that is the right value. Such a part would not be expensive at all since it does not have to handle any Voltage. 

Pick up a used Coda 8 amplifier. Good amount of Class A power and lots of current to produce fast and articulate bass. 

Coda Technologies S5.5 Class A amplifier is what I meant to copy and paste.

As stated previously, whilst not owning one, well respected listeners I’ve interacted with love it.  Good hunting.

@atmasphere 

"I repaired an SET recently that made 12 Watts. When I tested power bandwidth, I found that it hit a wall at 90Hz. Below that its maximum output power without excess distortion dropped; at 20Hz it could only make 1 Watt."

If this amps output power at 20Hz is one watt then you could assume it's a one watt amp and 20Hz is the bottom of it's power bandwidth. If the THD exceeds 1% at 20Hz and up the frequency scale to 20Khz, its probably even less which would be perfectly in keeping with an SET using a single 300B output tube. Consumers see tubes amps with a rated output of X watts @ 1Khz and think they have a powerhouse when in reality when you consider power bandwidth over the range of human hearing the actual output is barely a fraction of what they're hoping it is. Just tubes.

If this amps output power at 20Hz is one watt then you could assume it's a one watt amp and 20Hz is the bottom of it's power bandwidth.

@faustuss  That would be a lot (most) of SET products!

Most SETs have their power rating at a point where you can see the sine wave on an oscilloscope clearing being distorted. That’s a lot more than just 1% which is an arbitrary value. So I would not fault an SET that could make the same power at 20Hz as it can at 1KHz, but the only SETs that can do that are either parafeed or use the Berning ZOTL output circuit, which uses an air core output transformer. 

Since its the bass where most of musical energy exists, IMO its important for the amplifier to be able to make full power in that region. Our OTLs can make full power to 2Hz, which nicely solves the usual increase in distortion you see with almost any transformer coupled tube amp. 

These days though there are class D amps that are just as smooth in teh mids and highs as the best tube amps and don’t have any bandwidth issues. But some people really can’t get their head around that so here we are :)