reverb and effects

This amp will have two spring reverb tanks, to produce a true stereo image.  Even with identical tanks, there will be subtle differences between the left and right signals, leading to a stereo effect.  But it will be possible for users to install different tanks for left and right, e.g., tanks with different numbers or lengths of springs, or different decay times, to obtain a more dramatic stereo effect.  The left and right return signals can each be separately mixed from full-dry to full-wet, enabling unusual stereo settings such as full reverb from one speaker and full dry tone from the other.

The spring reverbs are bypassed if external effects are plugged into the return jacks; the reverb and effects loop share the same bypass relay, and it's not possible to have both spring reverb and external stereo effects active at the same time (although one could plug a mono effect into one channel, while keeping the spring reverb in the other channel, for some interesting sonic variations).

For an unusual capability that no other amp provides (that I know of), the reverb and effects loop will have a six-position switch to select the "send" source.  In the rightmost position, the send will come from the end of the signal chain as normally expected, i.e., from the output of the second EQ.  But turning the control to the left will select progressively earlier points in the chain: the output of each gain stage, the first EQ, or the output of the first input stage itself.  Thus, depending on the settings of the EQs and gain stages, and depending on the position of this source selector knob, the reverb or external effects can process a much cleaner early signal, with later distortion and EQ colouration only applying to the "dry" signal.  There are not a lot of examples of this type of sound in the recorded canon, but I suspect it may prove musically useful.

In addition to the spring reverbs and the main (final) stereo effects loop, there are two earlier points where mono effects can be inserted: each of the two active EQ modules provides an effects loop, switched by the same bypass relay as the EQ.  Plugging an effect into the return jack overrides the output of the EQ, but two send jacks are provided, pre- and post- EQ, so the external effect can either replace the EQ, or can cascade after it.

The motivation for providing these earlier mono effects loops in addition to the main stereo loop, is that just like in the case of EQs, there can be a radical difference in the tonality produced by an effect when placed in front of the distortion stages, as opposed to afterwards.  Of course one could plug the effects into the chain ahead of the amp entirely, but then the guitar sees the load of the effect circuit, whatever that may be; with the arrangement here, even the earliest effect position still has tube buffering, so the guitar always sees the same input circuit (which is a one megohm load to ground, with 34 kohms series into a tube grid: i.e., the traditional Fender-style guitar input).

None of the effects loops has its own dedicated buffering; instead, I simply exploit good buffered "send" locations where they already exist in the chain.  Thus, the external effects units themselves are responsible for not loading their inputs too much, and for driving their outputs the "right amount" to re-insert into the signal chain.  And probably the most inconvenient part, the effects units must be able to handle "raw" tube-circuitry signals, which are nominally supposed to be at line level, but which can potentially climb much higher, into the realm of several dozens of volts peak-to-peak.  Tubes don't especially mind this kind of input overload, but solid state circuits certainly will!  (Effect sends from tube circuits often include some type of pad or divider, to reduce the signal level, and then of course added gain on the return inputs to compensate.)  Probably it would be more accurate to call these "patch points", rather than "effects loops", but I stick with the more widely understood terminology.