Vox Grenadier XII Columns

More wreckage from JMI / Thomas Organ

Vox Grenadier XII Serial Plate

These 4 x 12" cabinets are actually quite rare in the UK. Vox columns over here are normally the 4 x 10" version. They came from my old friend Robert Harper who bought and used them in the States before moving over here.

 

According to the serial plates, these were made in Sepulveda, California by the Thomas Organ Company under licence from JMI.

 

At first glance the grill cloth looks as though it's been replaced (the pattern is going sideways). However, North Coast Music point out that the first production run from Thomas was built like this until they made some wider cloth.

 

see http://www.voxshowroom.com/us/amp/grenXII.html​

 

That puts this pair at around 1965.

1. Introduction

The Grenadier name was applied by Thomas to a number of different PA columns and you need to look at the V number to see which is which. The JMI version of the 4 x 10" was available in the UK as the LS40 and the 4 x 12" as the LS60.

 

"LINE SOURCE", indicated on the Serial plate, simply means that the speaker units are mounted in line, one above the other. This is generally considered to give the best sound distribution pattern for public address work.

 

Details on the web are slightly contradictory so please take the following numbers as a best guess. More information from other owners would be appreciated. Details of the Grenadier X are courtesy of North Coast Music.

 2. The V121

These particular columns are type V121 and each has four 16 ohm, 12" speakers wired through a switch which allows 16 ohm or 4 ohm operation. Connection to the amplifier is via a three pin XLR plug as used on the early AC50.  What's left of the plastic corner protectors have early, single nail fixing.

 

You can see the sideways grill cloth diamond pattern in the pictures below taken at Apollo Park in the States in 1979. The guitar players are John Hovsepian and Dave Payne with Rob Harper on vocals. The amp in the bottom, right hand corner is the Gretsch Pro Bass 6170 featured on another page in this site.

 

I reckon John's just realised that the mic pop filter is Rob's sock.

Rob explained where the photographs were taken (6515 AMS/PMEL is a department of the US Air Force).

"Apollo Park is a recreational area (county park) on the edge of Lancaster, CA. There's a lake and picnic areas. The area we are playing at is a static display of an Apollo space capsule, couldn't tell you now which one. We had noticed that even though the display was a closed (locked) display for viewing only, there was a weatherproofed mains outlet on the side.

The outlet proved to be live so our concert idea began to take form. On the day of our lab picnic (6515 AMS/PMEL [Precision Measurement Equipment Lab]) we performed for our co-workers and their families but the sound drew people from all over the park and we had more strangers than co-workers when we finished. The picnic must have been sometime between July and September 1979. Wish I could be more precise."

The drawing below shows the Grenadier speaker wiring as found.

Vox Grenadier XII Internal Wiring

There is an additional 1/4" jack socket at the top of each rear panel for connection to an external, high frequency horn (don't try to use it as an input).

Thomas designed some of their power stages to run into 2 ohms but a normal British PA amp will need to be set to 8 ohms and the speakers to 16 ohms. That assumes that the amp has two speaker sockets connected in parallel.

Vox Grenadier XII View 1
Vox Grenadier XII View 2
Vox Grenadier XII View 3
Vox Grenadier XII View 4

3. Speaker units

The speaker codes read 12K5-9 (chassis) 465-639 (chassis) 33-5084-6 (magnet) and P4561 (cone).

The source codes are consistant and all read 465-639. This would make them Oxfords made in week 39 of 1966 ( the code doesn't show which decade but I know where these came from ). The actual speaker type is 12K5-9 (12" 25watts peak power ?). Testing one of the chassis in free air gave a resonant frequency of about 100Hz.

 

The magnets are marked 33-5084-6, which is a Thomas factory part number, 33 being the prefix for loudspeakers. Assuming that the individual speaker chassis are rated at 25watts peak each, then Vox UK's 60 watts per column (LS60) seems reasonable.

 

The speaker frames are gold under a layer of white corrosion and have some rubbing coils and a torn cone. Even so, the sound is encouraging and they're worth bringing back to life.

Pictures above show one of the loudspeakers before and after cleaning. The remains of the gold lacquer can be just be seen.

4. What's left?

The condition leaves a bit ( no, let's face it, everything ) to be desired. The cabinets are made of 22mm chipboard ( particleboard ) with an 18mm back panel and have absorbed a large amount of water. One column was stripped a long time back and comes as a kit.

 

Unfortunately, at the moment, they're at the back of the queue so progress may be a bit slow.

The cone damage is possibly repairable but the spider will have to go.

5. Oh no...not again!

If you look at the Gibson Mercury page, you'll see what happens if a plywood cabinet gets to stand in water. If you look below you'll see what happens to a chipboard one.

Picture on the left shows two new speaker protection strips glued in and ready for sanding. One was missing and the other collapsed from old age.

22mm chipboard is a bit hard to come by, but you can buy it as P5 flooring in 2400mm x 600mm sheets for about £12.

 

That's a lot of board but it can be rebated with a router around the edges and used for the back panel as well.

 

Left to right below (as if you didn't know):

The cabinet trimmed back:  The new bottom panel trial fitted (oversize):  Glued, shaped and filled ready for the stringing slots to be cut.

Far left is the new back panel rebated around the inside edge to compensate for the extra chipboard thickness.

It also needs room for slightly over two layers of material around each edge or it won't fit when it's covered. The old Thomas material is very thin so anything much heavier will bring the screw holes very close to the edge.

Quick update. Managed to salvage the original back panel so that was a waste of time. Nice to be out in the sun though.

Below left: the quick way of marking out the stringing slots with a chalked line (many thanks to my lovely assistant - you'll need one unless you've got three arms). Centre: both slots cut. Right: original batten and T-nuts glued and clamped.

6. Progress so far

 

The 1960s vinyl (removed and stored over a decade ago) had shrunk in all directions and part of it was missing. You can still buy similar material from North Coast Music, but a) it would cost an arm and a leg to import it and b) you'd never get your money back.

Vox Grenadier XII column

The back panel covering was toast, so it's been replaced with a fairly close Fender pattern and used to patch in the shrunk material. That's actually the original chipboard panel underneath (the XLR was off centre from new).

You can see the outlet for the add-on horn unit towards the top. Once again, it can't be used as an input.

Vox Grenadier XII column

The speaker coils have been persuaded to stop rubbing and the split cone has been patched with tissue and thinned PVA.

As far as I know, new cones and voice coils aren't available.

The extra holes around the second speaker down appear to have been done at the factory after one hole broke through at the edge

With a music signal from a CD the column sounds quite good, although there's a very obvious lack of bass response. That said, it was designed to project vocals over the rest of the band and the examples I've heard live did that very well.

Vox Grenadier XII column

You can see one of the patches about 12" above the locking ring. It had to be fitted to line up the existing screw holes. There are several more around the cabinet.

The covering all around the front, to the right of the string line, is made up of strips cut from the original back panel material.

Still needs gold string, single pin corners, new front cloth and repairs to the stand.

Still looks a mess, but it works and things can only get better. Mind you, isn't that what the Labour Party used to say?

7. Tilt -back legs

 

Looks like the legs on this one have been around the block a few times. They were originally brazed together with brass (or bronze) filler wire. One end just needs re-brazing but Conan The Welder's been at the other one. It's perfectly possible to weld thin wall steel tube, but it's very easy to just blow away the material with too much current.

Vox Grenadier XII Tilt Back Leg

Don't forget to fish out the remains of the old rubber feet before setting fire to them.

Time for some metal bashing (nice to be working in inches again).

Vox Grenadier XII Tilt Back Leg
Vox Grenadier XII Tilt Back Leg
Vox Grenadier XII Tilt Back Legs
Vox Grenadier stand repair

The crossbar is beyond repair, but where do you find imperial sized 3/4" x 1/16" chromed steel tube?

Well it helps if your lovely assistant is an inveterate skip diver. She just happened to bring home the very thing a few years ago.

LEFT: Old weld cleaned off and new section ready for brazing.

Back soon.