Building on the (eventual) success of my
1U rack-mount spring reverb unit, I have been pondering a build based on Fender's 6G15 valve-driven spring reverb.
The original form factor involves a chromed steel chassis mounted in a tweed cabinet, intended to be perched atop your non-reverb Fender combo. But I want this for home use only, so I came up with the idea of making a 3U rack-mount version. To keep the cost down, most of the parts will not be new. The majority are pictured below, including:
3U rack tray left over from my 2005 studio build and relegated to the loft ever since;
Old Accutronics 9AB2C1B (gift from a friend - may well have come from a dead Peavey combo);
PT and OT from a Harley Benton GA5 (Epi Valve Junior clone) - these provide the right voltages and impedance ratios respectively;
Hammond 4H 50mA choke (bought new - used chokes seem to cost no less);
JJ 12AT7, TAD 7025, RCA 6K6 (reputedly sounds much better than the 6V6 employed in the reissue units);
Recycled pots and sockets; and
Worn-out Behringer RX1602 - this will provide the actual chassis, as well as the mains inlet and switch. The valves will sit on top of it behind the transformers, rather than being mounted on a separate surface.
I still need to source eyelets and eyelet board, valve sockets, and some 0.8mm plastic sheet material to face the front panel. Still, I can get started stripping out the Behringer - there's a nice toroidal transformer in there, mmmm....
Wish me luck!
Comments
(1) Finding the position and orientation of the PT to cause the least hum in the reverb tank's output transducer. The PT is connected to the mains, and all the other leads protected in chocolate block connectors. The orange lead is connected to the reverb return of an existing amp.
(2) Finding the position and orientation of the OT for least hum induced by the PT. I have a pair of headphones connected to the OT secondary.
EDIT: By OT I mean the reverb tank driver, which is acting as an OT. You could connect an 8ohm speaker instead of the reverb tank and have yourself a little single-ended amp.
(3) Finding a place for the choke out of the way of the eyelet board.
*An Official Foo-Approved guitarist since Sept 2023.
I cut away a section of the aluminium channel that forms the front of the Behringer chassis, to allow easy access to the pots and that side of the eyelet board. Then I drilled and cut all the holes for the valves, transformers, audio sockets, and pots. I will have some more drilling to do later when it comes to installing the eyelet board and fitting the chassis into the rack tray.
The two small empty holes are for the standoffs, the four larger ones are for wire pads-throughs.
I fitted the components and leads to the board today. For the most part, eyelets are proving easier to work with than turrets, especially when re-doing connections (ahem!) but there is a physical limit to how many wires you can fit into an eyelet. I ended up making a preamp ground bus out of a piece of solid copper wire. There will be some signal screens to take to earth, and no way would I have been able to fit them all into the available eyelet holes.
On reflection I probably didn't need to create pass-through holes - I read on another forum that they were chiefly intended to stop the leads getting knocked off when made-up boards were chucked into parts bins!
Today I cut the plastic face plate and glued it in place, drilled the mounting holes, and mounted the pots, sockets, and pilot light.
I ended up installing two more small terminal boards. One was for the HT because the leads from the PT (red twisted wires) didn't quite reach the board. This turned out to be an advantage, as I was able to use wire with a slightly slimmer core from terminal board to eyelet board, which meant I could actually get it into the eyelet! The other was for the mains supply, as I didn't have anywhere else to patch in the leads from the neon pilot lamp.
All that's left now is the heater supply - the orange twisted wires from the PT will go to the terminal strip where I have made an artificial centre tap with two 100R resistors. All being well I should get this finished at the weekend