When it comes to reverb with real depth, then the Fender Reverb unit is without a doubt the king.
Although not a typical LoW project, due to its class and simplicity we have decided to include it in the LoW series. Because the components such as chassis, shell, and transformer from other projects are reusable, the implementation is uncomplicated.
Since the Fender Reverb Unit is extensively documented and there are countless pages on the Net that deal with it, we can limit our
discussion to circuit details which differ from the original.
The biggest difference is the driver tube (a JJ EL844) and the transformer used. The original uses a 6K6; the reissue uses a 6V6, and a transformer with a 6K primary.We decided to use the EL844 and the transformer from the integrated Fender Reverb circuit. This has a considerably higher primary impedance as it is normally used with a
12AT7, but it also works with the EL844. Furthermore, it is less expensive and easily available, which compensates for the slight mismatch.
Nevertheless, the original transformer can be used, or another single-ended OT, such as the Hammond 125BSE. Instead of an EL844, an EL84 can be used, but this tube draws more current, and has no other advantages, as the sound remains the same. Anyone who wants to duplicate the original circuit exactly can use a 6K6 or 6V6, but the chassis must be modified to accept the octal socket, and the cathode resistor must be changed.
The pots were also changed. The original used linear pots, which to some extent led to an "unusual" control response. Where it made sense, we replaced these with logarithmic pots, which give a familiar "feeling" to the controls.
That's it; straight and simple. Regarding the reverb tank itself: in the original, a 4AB3C1B tank was ussed. This results in the Reverb Unit with veeerrryyy looong reverb, and is also physically very large, so that we have decided to use a short 8-series tank. This tank also produces a long reverb. Whether such a long reverb is necessary is up
to you. The 8AB2A1B is an alternative with a shorter (medium) reverb, and permits finer adjustments. The choice is yours.
The construction follows the series standard with the Mini-PSU power suppy and the small LoW chassis. Since room for the reverb tank must be found, we recommend you use the head shell from the shop, if you don't want to build the shell yourself. All necessary components are available in the Shop.
Schematic & Layout as PDF
The a kit is available in the Shop.
Caution is necessary. Even though this isn't a particularly powerful amp, it nevertheless works with voltages which are potentially lethal. This amp is NOT appropriate for beginners !
Reading and understanding schematics, use of measurement devices, and good experience with voltages over 60V are prerequisites for the successful completion of this project.