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.
For whatever reason, the engineers at Fender added seven additional components to the output stage, effectively turning it into a semi-cathode-biased output.
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.
But don’t lose sleep over this, as most post-blackface “improvements” can be returned to pre-’68 specs, yielding a pretty toneful amp. I hope that sheds a little light on your amp, but remember: It’s only a bad amp if you don’t like it!
Jeff Bober is one of the godfathers of the low-wattage amp revolution.
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.
In 1968 Fender changed to the “silverface” control panel.
The circuitry was altered as well: There were changes to the bias and phase inverter circuits and, most important, the output stage.
This boost is activated via a master volume control with a push/pull switch. From the most unlikely of places: the reverb drive signal!
The reverb drive circuit in most tube-driven reverb amps is actually similar to a small, low-power, single-end output stage.
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.