Can I use a Torpedo product with a transistor amplifier ?
The Torpedo products featuring a loadbox (Torpedo VB-101, Studio, Live, Reload, Captor) can be used with amplifiers, as direct replacement for a speaker cabinet. See here for more details.
As you surely know, a speaker cabinet is not designed for a particular type of amp. There are no cabinet designed specifically for solid state amps or for tube amps. There are just speaker cabinets. A loadbox being just a replacement for a speaker cabinet, the same logic applies. This means you can use your Torpedo loadbox product with a transistor amp, just like you would use the same speaker cabinet on either a tube amp or a solid state amp. There are no limitation here.
And if you were looking for information on Torpedo products, you can stop here! :)
The rest of the article is a more detailled technical discussion on this issue as a whole, it will take a detour to other designs, other products, other manufacturers, and will actually not be about the Torpedo loadboxes. If you are curious about electronics, or if maybe you found information elsewhere that seems to contradict what was just stated, please continue reading. We'll see why you may have found this information, and the technical reason why you shouldn't worry about Torpedo products.
This question actually raises a surprising issue. The fact is, this does not apply to all loadboxes that exists out there. Some loadboxes are designed in a way that makes them unsuitable for some amps. Some manufacturer actually do warn about this, and specifically say that their loadboxes shouldn't be used with solid state amps. So what makes the Torpedo loadboxes OK for use with any amp, while some other loadboxes aren't ? And why solid state amps in particular ?
The basic explanation is: these unsuitable loadboxes ground the sleeve of the speaker jack. Which results in a short-circuit between this point and the ground of the amp. And it's at this point that you may find a difference between solid state and tube amps.
Most tube amps use voltage feedback (if they use feedback at all), and have their output (the secondary winding of the output transformer) referenced directly to ground. This means that there is nothing to short-circuit, and this simple design works OK.
But some solid state amps uses other architectures, like current feedback, which inserts a resistor between the sleeve of the speaker jack and the ground of the amp. This resistor is then short-circuited by the unsuitable loadbox, resulting in an amplifier that don't work anymore.
Some solid state amps may be used bridged, like many stereo PA amps, or may be bridged by design (this is the case of BTL, Bridged Tied Load amps), in which case the sleeve of the speaker jack is effectively the output of one side of the amp. In this situation, the unsuitable loadbox simply short-circuits a whole amp! And I'm sure you can guess how this is not a good idea...
Some other solid state amps use even more advanced architectures, like class D. And more generally, transistors allow for many, many more different architectures than tubes do. Among this variety, some of them are bound to use something between the sleeve of the speaker jack and the ground. And that's why you may find unsuitable loadboxes with warnings against use with solid state amps.
But let's rewind a little. We just said "most tube amps" just a few paragraphs earlier, and that's a key point: while it's not that common, tube amps designers can nonetheless take advantage of advanced architectures. Some tube amps manufacturer simply reverse the polarity of the speaker output, which would lead to a general short-circuit when used with an unsuitable loadbox. Stereo tube amps can be bridged. Basically, it's impossible to predict everything a designer might do (which is kind of what's great about electronics BTW!).
On the other hand, many solid state amps have outputs directly referenced to ground, and will not cause any problem when used with an unsuitable loadbox. In the end, it's just too much of a simplification to say these loadboxes can be used with tube amps and not with solid state amps. The whole picture is more complicated than than.
And more to the point, these limitations are due to design choices, not to the inherent nature of loadboxes. By using other designs, it's perfectly possible to avoid this altogether. And that is the case of the Torpedo loadboxes: they are designed in a way that simply avoids this whole issue.
So let's say it again: all of these limitations do not apply to Torpedo loadboxes! They are designed to act as true speaker replacement, with no direct ground connection. As a result, you can use them with any amp you like without issue (providing you just respect the power rating).
This fact is, with many other things, what makes the Torpedo products what they are: high quality, reliable products, that are not limited to specific uses, but can be used a generic tools in any situation.