The Reverb and Vibrato sound stunning; one of our favourite vintage amps here at Soundgas, we've held on to it for some time as our main demo amp - see below for an example. The usual signs of wear are showing, such as minor scratches to the face and a bit of wear to the grill cloth and tolex, but certainly nothing that affects the performance of this fantastic amp.
Some players actually prefer these models, however, because they tend to compress more easily than any other Twin.
According to the dates on Fender schematics, these “improvements” only lasted for a year.
But instead of being connected to a speaker, the output of the transformer in the reverb drive circuit is fed to a transducer in the reverb pan.
It’s similar to a speaker, except instead of driving a cone, it drives a spring. In reality, the result was far from stellar, and I’m not sure I know anyone who actually uses this feature.
As you can imagine, a signal derived from this circuit could have substantial level, which could easily overdrive a preamp tube—and since the overdrive comes from a little tube power amp, it should sound pretty good. I’ve never ascertained if this is because the reverb drive signal simply doesn’t sound as good as you’d expect, or because of where this signal is applied in the amp.
Either way, this under-whelming overdrive tone—together with the master volume and other post-1967 circuit changes—is why your amp is, in your words, maligned.
Blackface Twin Reverbs are the most coveted versions of this amp.
With their stated power of 85 watts, they are the most powerful Fender amps of the era.
You can easily identify these 1968 amps by the silver-metal band around the perimeter of the grille cloth.
The 1969 schematic revision shows a return to the standard fixed-bias, 100-watt output-stage configuration, though the bias and phase inverter changes remained.
The tube is fed a signal (from channel 2, or the “vibrato” channel, in the case of Fender reverb amps).