Rack-mount 6G15 standalone reverb build NOW WITH AUDIO

Keefy

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!

Keefy

Behringer chassis stripped out. The mains switch is only single pole but I can live with that. I harvested the toroidal transformer, a pair of 15V regulator chips, and a bunch of nuts and washers; the rest is bin fodder.

Winny_Pooh

Cool!

Keefy

Rough layout of main components. I have left off what was the top panel of the Behringer chassis and inverted it, and removed the rack mount ears. I have yet to decide how the chassis will attach to the 3U shelf. The reverb tank is supported on two of those tie bars used to give solidity to the rack tray - this will allow the cables to pass beneath it. Input, output, and mains cables will connect to the rear of the Behringer chassis, with the signal cables terminating at my studio patch bay. I am considering whether to fit an extra input and output on the front panel but I've yet to come up with any advantage to this.

Keefy

Eyelet board incoming - time to get to work ona full-size layout.

Keefy

Transformer fun:

(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.

Gassage

Following....

Keefy

I've pretty much finished the layout plan - below is the view into the open underside of the chassis. A few things to point out:

1. I have incorporated some popular mods, i.e. 33k grid stopper and 25uF cathode cap on the first stage.
2. Fender's schematic shows 40uF filter caps, Mojo kit goes for 22uF, I have compromised at 33uF. The original design has these caps in a separate 'dog house' but I have put them on the end of the eyelet board.
3. All my audio connections are on the rear panel.
4. I have taken note of the Valve Wizard's advice on multi-star grounding (and the painful lesson of my Rocket build!) so each amplification stage has its own complete earth return, and those grounds are then taken to a single point on the chassis.
5. I made some further amendments to the input and output grounding arrangement after taking the photo - I am getting through a lot of Tippex!

Keefy

More parts have arrived. My first eyelet board build...

PeteC

Hope you find the eyelet construction is easier than turrets.  I certainly do.  Good luck with it.  

Keefy

PeteC said:

Hope you find the eyelet construction is easier than turrets.  I certainly do.  Good luck with it.  

Cheers! I'll be exploring ways of setting the eyelets before I launch into building the board.

PeteC

If you have a drill press then a dowel above in the chuck and a round nosed bit in the vice underneath and it’s a breeze.  If not then you can put a large posi-drive bit facing up in a bench vice and tap the eyelets from above with a hammer to seat them and splay the rivet underneath.    

Keefy

I have a cheapo drill stand - it is operated by a lever rather than a wheel. I also have a leather hand punch and a hand setting tool for larger eyelets, so I'll see what I can bodge together from that lot.

Keefy

Today I have mostly been doing metalwork - not my favourite job, just gotta do it.

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.

Keefy

Today I installed the transformers and choke, the valve sockets, pots, and the in/out jacks. For the pilot light I'm currently undecided between a big-ass jewel light, an LED in a bezel (which would also work off the 6.3VC AC with a suitable resistor), or a 240V neon.

Keefy

Today I cut the phenolic blank to size and marked up all the hole centres. They didn't come out quite as straight as I hoped! Then I set the eyelets, starting them off with finger pressure and finishing with a hand tool intended for setting larger eyelets into banners. There wasn't much eyelet protruding at the back, and they were very snug in the 3mm holes I had drilled, but I made sure they would stay put by spreading them with a countersink bit in my shonky drill press.

The two small empty holes are for the standoffs, the four larger ones are for wire pads-throughs.

Keefy

Yesterday I did the last of the chassis drilling and test-fitted the eyelet board. I used taller standoffs than shown, to give more clearance between some of the underboard B+ connections and the ridge where the steel and aluminium sections of the chassis overlap.

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!

PeteC

Looking good.  The pass thru holes are worth it.  They make for a more solid board once it’s all installed.  

Keefy

PeteC said:

Looking good.  The pass thru holes are worth it.  They make for a more solid board once it’s all installed.  

Cheers Pete!

Today I cut the plastic face plate and glued it in place, drilled the mounting holes, and mounted the pots, sockets, and pilot light.

Keefy

I had the day off today so I got busy with the wiring up.

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

mikem8634

I love this thread, even though I might as well be looking through a wizard's window.