Another Combo To Head Conversion Thread

[El Marin]

Hi there

I got time ago a JCM900 MKIII Master Volume, model 2101. I love it. The 2101 is 1x12" combo and I have it paired with a 1912 cabinet.

Te amp for me is a keeper. We gig from time to time, and most of the time we share the stage. I come from gigging a with Twin Reverb, really heavy load. The 2101 is smaller but quite heavy as well. As I said, most of the gigs we share the stage and amps. The idea is just carrying the head and connect it to any cabinet.

This is my rig now. Forget about the tweed head...

I was thinking on that question when I saw an empty head cabinet for 40€ in a Spanish forum... just too cheap to say no... So I got it and there we go!!

My idea is pulling out the chassis from the combo, installing it in the head cabinet and close the holes in the combo. Everything must be able to be dismounted and fitted back just in case. I got some plywood blanks and a real thin leather sheet and that part of the job is quite easy.

I am relative new to Marshalls, only one year with this amp, and would need some help if you are so kind...

I have been reading some threads about the amp and conversions like mine...

My amp has the impedance selector labelled like 4 (16) Omhs and 8 Ohms. I suppose combos really are 4 and 8 Ohms. I would like to be able of switching to 16. It would be as simple as installing a new speaker jack using the unused transformer cable, isn't it? Just a new hole

I will need to make a new faceplate as the old one will be flipped down 180º. I live in Spain and found Modullus in Scotland, still EU so far so no taxes. He will make me a new updown faceplate. Maybe with some cosmetic changes. Spinal Tap numbers, you know, these goes to eleven. Maybe change JCM900 to JCM666... well, my question related to the faceplate is: Do they just come out when pulling pots rods or are they glued? How do I pull it out safely. I have to send it to Scotland so he can exactly mimic the holes.

The back faceplate will be just updown as I will look at it mostly over the head

Your help will be much apreciated.

Just another pic of the amp and my 71 LP Deluxe

 

[El Marin]

I would like to make another question. What would you do? The head cab is the normal length of a Marshall head but my combo and 1912 are narrower. I already have a matching "Marshall" logo same size the combo and the 1912

Would you chop the head to fit the cabs or just order a longer faceplate to cover all the hole?

These are the photos of the empty head:

 

[Ghostman]

I would just make a new faceplate and backplate for the head. No need to cut the head down, or make a longer faceplate for your amp.

 

[Kinkless Tetrode]

If it was a plexi or a JMP style head box it would be real easy, because the front panel can be cut to fit the control panel of the chassis.

You might be able to do that using that head box, anyway.

Option 1) Remove the JCM800 style front panel and fabricate a JMP style front panel to just fit inside the front opening. You would install mounting blocks on the four corners inside. You could cover the new front panel with either grill cloth or tolex. You could also install the chassis up side down on the bottom, or right side up on the top.

Option 2) Fill in the remaining opening with matching gold colored inserts. The chassis would be installed upside down on the bottom.

Option 3) Trade the 800 style head box for a small box plexi head box. The 1987 (50 watt plexi) and JTM45 chassis are 17" wide and the control panels of the 1x12" combo chassis of the 900 era are also Approx. 17" wide. The Chassis can be installed top or bottom.

Make sure you get a thin piece of tin or aluminum to place on the inside of the head box under the or above the chassis as a shield. You will see this inside the stock combo cabinet once you remove the chassis.

 

[El Marin]

1) Remove the JCM800 style front panel and fabricate a JMP style front panel to just fit inside the front opening.

Yes, I think this is the best idea

Make sure you get a thin piece of tin or aluminum to place on the inside of the head box under the or above the chassis as a shield. You will see this inside the stock combo cabinet once you remove the chassis.

Thanks, I was aware of that. In other amps I have built I used glued Aluminium paper (yes, from the kitchen) with really good results.

Albeit the 2101 is with the valves pointing downwards, my intention is putting them pointing upwards. Let the heat fly away instead of cooking the circuit like now is doing

 

[El Marin]

Well... I made some testing and I don't like the look of a Big head on a small cabinet, so I am going to take the hard path and chop the cabinet, retolex with matching elephant tolex and keep all the mini-stack in a little size harmony

This photo shows what I mean... not nice. And I will have two 1x12" cabinets. I could sit the head over the two cabinets but most of the time I will carry only one or just the head. So, space wise talking... let's chop off!!!!!

 

[Kinkless Tetrode]

I know what what you mean. I hate it when a head overhangs the cab.

 

[El Marin]

I am working on it

Amp is out

Let's make a cabinet with this and some wood blanks



Used a Les Paul jackplate and covered with leather the back

Used some corners, covered everything with duct tape just to avoid rattles

Looks nice

Used some white piping just because it was there. Didn't had anymore so, this is what it is

The head cabinet is almost done. Tomorrow I will cover it in black tolex...

 

[El Marin]

OK
Let´s start with the head...

The amp swims inside this pool... No worries, let's chop

First strip the tolex out, with a hair dresser and some help

Measure where to start cutting

 

[El Marin]

First attempt... just cut the length... and I don't like it... too tall isn't it?

After measuring, got a more harmonious cab...

 

[El Marin]

Applying tolex...

Make the back cover...

And now, let's put everything together.... corners, feet, handles, amp, covers... and we have this...

 

[El Marin]

And, this is the final result...

And back to the rehearsal studio!!

Now, only need a new faceplate with letters I can read... next stage

 

[Kinkless Tetrode]

That looks great. And it packs 100 watts.

 

[El Marin]

That looks great. And it packs 100 watts.

Yes indeed.

Is a funny thing when I came to the gigs with the old combo people thought... look, he has a Valvestate ... until I plug it on

I have tested in the rehearsal studio with the amp and fin the close cabinet to sound better than the original combo. Tomorrow I will gig it but so far I am really happy with the change

 

[Wailing]

Hi El Marin

Sorry to go back to this thread, but I wondered if you had considered cutting the combo cabinet down to size rather than put the amp in another cabinet. I am guessing your desire to have the tubes on the top, rather than hanging down had made your mind up for you. I also imagine the side handles would have left a void that you would have had to fill. I have the same amp, and was considering selling, but now, thanks to your inspiration, think I will reduce the size and weight in the same way as you and keep it, however am tempted to use the existing cabinet.

Look forward to your reply... Wailing

 

[Dogs of Doom]

My idea is pulling out the chassis from the combo, installing it in the head cabinet and close the holes in the combo. Everything must be able to be dismounted and fitted back just in case. I got some plywood blanks and a real thin leather sheet and that part of the job is quite easy.

Hi El Marin

Sorry to go back to this thread, but I wondered if you had considered cutting the combo cabinet down to size rather than put the amp in another cabinet. I am guessing your desire to have the tubes on the top, rather than hanging down had made your mind up for you. I also imagine the side handles would have left a void that you would have had to fill. I have the same amp, and was considering selling, but now, thanks to your inspiration, think I will reduce the size and weight in the same way as you and keep it, however am tempted to use the existing cabinet.

Look forward to your reply... Wailing

His thought was to make it reversible...

Also, to be able to use the speaker. If you cut the cab down, you won't have a speaker cab.

If you ever plan on selling the amp, best bet is to have the cabinet untouched. Depending on your reasoning, if it's lugging around weight, & there's a good cab already there to plug into, you might simply remove the speaker, as that's a lot of the excess weight. The extra few inches of wood don't count for much. Your weight is all in metal (transformers & speaker magnets).

That's why, even if you just want to customize the cab, it's best to get a new cab & leave the original untouched. That way you can always sell it as original, or custom, or, add in the extra box. Once you butcher it, you ruin the value...