I have used a Graaf Gm20 for about 10 years before upgrading to a Wavac
Ec300b some 10 years ago. In short, there is no going back: while the
Graaf had twice the stated output power, making that power useful was
challenging: using autoformers to ideally match speaker impedance as
well as pretty regular rebiasing, neither of which is required by the
Wavac. If anything, the Wavac is faster than the Graaf despite its
transformers and the bass is substantially more solid. Botj amps are
classics in their line of design
What speaker were you using for this comparison?
The speaker can be an enormous influence when doing comparisons. There are other variables as well- for example most OTLs employ feedback (ours are some of the very few that do not). Some OTLs use pentodes as opposed to triodes. So they sound different; you can't categorically state that because you've heard one OTL you've heard them all and actually be telling the truth.
The distortion signature of the amplifier also plays a big role in the results. In a nutshell there are two types of non-linearities that show up. In single-ended circuits you get a quadratic non-linearity. In a differential circuit you get a cubic non-linearity. The cubic is preferred because its lower distortion; this is because even orders are cancelled and distortion does not compound as much from stage to stage as the signal progresses through the circuit. The 3rd harmonic is the primary distortion product and will mask the presence of the higher orders, allowing for a very smooth sound, but more detailed that that of a single-ended circuit because there is less distortion to mask it.
In a single-ended circuit the primary distortion product is the 2nd and there is usually a prominent 3rd. These two harmonics mask the higher orders so this circuit sounds very smooth as well. The problem is that as the order of the harmonic is increased, its amplitude falls off at a slower rate, causing more low level detail to be masked. But it has a rich sound due to the prodigious 2nd harmonic created.
When you combine the two (such as a single-ended input with a push-pull output), as a good number of OTLs (and other push-pull amps) do, algebraic summing occurs and there usually results more of the 5th harmonic (this has been known a good long time as Norman Crowhurst was writing about this 65 years ago...), which is the main reason SET guys object to the 'sound' of push-pull. But if the PP amp is fully differential you don't have this problem.
Since the feedback used in any tube amplifier is insufficient for it to really do its job, these distortion artifacts remain in the distortion signature.
In a nutshell you have to be really careful about making broad stroke statements; when comparing SETs and OTLs it can go both ways insofar as to which comes out on top. But all OTLs are **faster** than any SET (simply out of the fact that transformers slow down risetimes based on their bandwidth limits; this is simple physics); if it sounds 'slower' its likely because the amp is not matching well with the speaker in the high frequencies.
