Marshall 2203 to Super Bass Conversion Question

[father of fires]

Hello everyone!

I am thinking about purchasing one if these:

DIY Marshall JCM800 2203A 100w Tube Amp Kit VERSION 2

And modding it to Super Bass specs.

I have built a tube amp before (Fender Deluxe Clone) but that one was built entirely to the specs (no mods).

This will be a little more challenging.

I found these Super Bass specs on the Marshall Forum:

-Shared Cathode V1
-no brightcap Vol 1
-22n coupling caps after first stage
-no bypass cap V2
-tonestack parts 56k/250pf
-100n coupling caps after phase inverter
-100 ohm NFB from 8 ohm tap

Most of these make sense to me.

I believe the layout for the 2203 kit is split cathode. I'm not to keen on the differences between split and shared cathode.

I'm just wandering if the difference between these 2 pics is the difference between split and shared cathode. Split being the Super Lead and shared being the Super Bass. For this comparison, I am using the layout for a super lead (not a 2203) because the layout for that specific kit is a PDF file and I don't know how to edit it.





The super bass looks the most like my Fender Deluxe which I believe was shared cathode.

Is there any other differences?

Is this a stupid idea to begin with?

Thanks for reading!

[father of fires]

I guess the tube gurus don't have wake up as early as I do!

[MAMMOTHvolume]

that kit is very different to a super bass, buy a weber super bass kit

[projectMalamute]

Schematics for both here:

Marshall Amps Info & Schematics

The biggest difference is the first gain stage right after the input, the channels in a 1992 JMP are in parallel wheras the JCM 800 cascades the two in series. Also, the JCM 800 has a master volume. Other than that I think it's just swapping a few component values in the tone stack and a couple other spots.

I'm actually thinking about modding my Traynor YBA-1 to make the input section like the JCM, the exact opposite of what you are trying to do.

[father of fires]

Originally Posted by projectMalamute

Schematics for both here:

Marshall Amps Info & Schematics

The biggest difference is the first gain stage right after the input, the channels in a 1992 JMP are in parallel wheras the JCM 800 cascades the two in series. Also, the JCM 800 has a master volume. Other than that I think it's just swapping a few component values in the tone stack and a couple other spots.

I'm actually thinking about modding my Traynor YBA-1 to make the input section like the JCM, the exact opposite of what you are trying to do.

So split equals cascaded and shared equals parallel?

[projectMalamute]

Originally Posted by father of fires

So split equals cascaded and shared equals parallel?

No, split means that each side of the tube has it's own cathode resistor and bypass cap, while shared means that both sides of the tube have the cathodes tied together, using a single resistor and bypass cap.

The old Marshalls/Traynors/Bassmans(Bassmen?) have two channels, each of which uses half of the first 12AX7. The two are combined in parallel.

In the 2203/2204 circuit the low gain input is like the input on a JTM/JMP. Input->gain stage->volume->on to the cathode follower and tone stack. The high gain input goes in to it's own gain stage and then in to the other gain stage (the one used by the low gain input) in series.

Look at the schematics I linked to.

[MAMMOTHvolume]

https://taweber.powweb.com/store/kits_60b.htm#8cm100 6m100 is the one you want!

[projectMalamute]

Originally Posted by MAMMOTHvolume

https://taweber.powweb.com/store/kits_60b.htm#8cm100 6m100 is the one you want!

Yeah, that looks like the regular Marshall.

to the OP: I just re-read your first post, are you thinking that the JCM 800 is the same thing as the Super Lead? They are different amps.

[father of fires]

Originally Posted by projectMalamute

Yeah, that looks like the regular Marshall.

to the OP: I just re-read your first post, are you thinking that the JCM 800 is the same thing as the Super Lead? They are different amps.

I know they are different amps. I wanted to know the difference between split cathode and shared cathode. I know that a Super Lead is split and a Super Bass is shared but I didn't know what that meant.

I was going to use the 2203 kit because it would have most of the components that I need. I assumed that the 2203 would be split cathode like the Super Lead because they are both guitar amps. I figured that if the difference between split and shared was the different wiring in the V1 position between the two picks I posted, then I could just wire the v1 of the 2203 like the Super Bass. Then make the other cap and resistor changes like I mentioned in my 1st post.

I didn't want to buy a Weber kit because of the lower quality of the components.

[projectMalamute]

Originally Posted by father of fires

I know they are different amps. I wanted to know the difference between split cathode and shared cathode. I know that a Super Lead is split and a Super Bass is shared but I didn't know what that meant.

I was going to use the 2203 kit because it would have most of the components that I need. I assumed that the 2203 would be split cathode like the Super Lead because they are both guitar amps. I figured that if the difference between split and shared was the different wiring in the V1 position between the two picks I posted, then I could just wire the v1 of the 2203 like the Super Bass. Then make the other cap and resistor changes like I mentioned in my 1st post.

I didn't want to buy a Weber kit because of the lower quality of the components.

The reason I ask is because the list you have up there is the changes between a Super Lead (circuit 1959) and a Super Bass (circuit 1992). The differences between the JCM 800 (circuit 2203) and Super Bass (1992) are more substantial, including the entirely different input section and the master volume.

[father of fires]

Originally Posted by projectMalamute

The reason I ask is because the list you have up there is the changes between a Super Lead (circuit 1959) and a Super Bass (circuit 1992). The differences between the JCM 800 (circuit 2203) and Super Bass (1992) are more substantial, including the entirely different input section and the master volume.

Thanks for your help so far.

OK, let me start over.

I want to build a Super Bass.

I plan to use a Super Bass schematic.

The JCM800 kit seems like will have most of the parts I need. Transformers, sockets, tag board, pots, some of the caps and resistors, etc. For under $500.00.

I can get a chassis from MOJOTONE for around $70.00 and I plan to build a headcase (or buy a cheap one somewhere).

While doing my research I came across an unfamiliar term (split/shared cathode) and I was looking for some clarification.

Thanks!

[KramerBassFan]

If you want a Superlead/Bass, built a Weber 6M100.

It will cost about as much as that Triode Electronics kit.

I always reckoned... if your gonna do it, do it right, from the beginning.

I built a 6M100, and it works quite well.

I also used Digikey caps, and resistors. Everything else from them is decent.

[father of fires]

Originally Posted by KramerBassFan

If you want a Superlead/Bass, built a Weber 6M100.

It will cost about as much as that Triode Electronics kit.

I always reckoned... if your gonna do it, do it right, from the beginning.

I built a 6M100, and it works quite well.

I also used Digikey caps, and resistors. Everything else from them is decent.

I was all interested in Weber kits for a while but then I started reading reviews and they all said the parts were junk. It kind of scared me off so I have been looking for a kit with better parts that didn't cost as much as a real Super Bass. I know you followed the schematic but even you bought most of your own parts. Would you say that you came in under $500?

[KramerBassFan]

Yes.

I bought my own caps, resistors, and other stuff like that from digikey.

I got a full sheet of baltic birch marine ply

Enough tolex/piping to cover it

The biggest chassis Hammond MFG makes

And a full set of shaugang tubes.

All in all, cost me roughly $500, give or take $50, and 40 hours of work.

I too would avoid Weber caps and stuff like that, but their other stuff - tube sockets, neutrik jacks, carling switches, all are decent grade stuff.

[Bassmec]

Originally Posted by KramerBassFan

Yes.

I bought my own caps, resistors, and other stuff like that from digikey.

I got a full sheet of baltic birch marine ply

Enough tolex/piping to cover it

The biggest chassis Hammond MFG makes

And a full set of shaugang tubes.

All in all, cost me roughly $500, give or take $50, and 40 hours of work.

I too would avoid Weber caps and stuff like that, but their other stuff - tube sockets, neutrik jacks, carling switches, all are decent grade stuff.

I too would just buy the right transformers and lace it up like a good'n out of a parts list of values. leaving quality up to my
control.
I don't like kits that use the wrong transformers, the new drakes and partridge are out of metric laminates which are of a different material and sized thicker than the original imperial sized marconi stock.
Sowters have stock of original imperial laminates and wind as per the original spec, or if your like me, want extra! they will make a custom output transformer that makes a mercury fatstack look rather puny.

Its all in the transformers!

[father of fires]

Originally Posted by Bassmec

I too would just buy the right transformers and lace it up like a good'n out of a parts list of values. leaving quality up to my
control.
I don't like kits that use the wrong transformers, the new drakes and partridge are out of metric laminates which are of a different material and sized thicker than the original imperial sized marconi stock.
Sowters have stock of original imperial laminates and wind as per the original spec, or if your like me, want extra! they will make a custom output transformer that makes a mercury fatstack look rather puny.

Its all in the transformers!

But can I buy the "right" set of trannys for price I could get decent ones in a kit?

[KramerBassFan]

The right set of trannys would cost as much as the kit.

I was looking for Marshall Major trannys, and they were only in europe, and would have cost me something like $1,000 usd.

This reminds me of the transformers on my Ampeg V4... they are EASILY twice the size of Weber 100w trannys.

[BassmanPaul]

Marshall amps did at one time use smaller iron than was really needed for the service. Proper sized and quality transformers are what a tube amp needs for bass. I too would roll my own as I have done many times. Hammond transformers you can rely on. They are built like tanks and I have yet to see a faulty one. Mercury Magnetics is another company who wind superior transformers.

If you do decide to go with a kit, build it as designed. Once you know everything is working properly you can amend it as you please. Trying to build one amp from a kit for another could lead you into stability problems.

[father of fires]

Originally Posted by BassmanPaul

Marshall amps did at one time use smaller iron than was really needed for the service. Proper sized and quality transformers are what a tube amp needs for bass. I too would roll my own as I have done many times. Hammond transformers you can rely on. They are built like tanks and I have yet to see a faulty one. Mercury Magnetics is another company who wind superior transformers.

If you do decide to go with a kit, build it as designed. Once you know everything is working properly you can amend it as you please. Trying to build one amp from a kit for another could lead you into stability problems.

I thought about this as well. I was on the fence as to whether I should build the kit and have a bitchin' JCM800 that I don't need or go right ahead and build what I want.

They don't really tell you who makes the transformers in the kit but since they are USA made I was hoping they would be better than Chinese ones (like Weber).

Outside of the mystery transformers, I don't believe I could buy all the other parts (Handmade in USA Turret Board, Mallory 150 series capacitors, JJ Power Supply Caps, High Quality Resistors, Alpha Potentiometers, etc.) for cheaper.

[father of fires]

I must admit that I've only ever played my buddy's JMP 2203 (pre JCM800 series). That was only for a few minutes a couple of years ago.

Before I invest all this time and money into an amp I've never heard, I think I should try to find a Super Bass locally that I can play through.

Anyone near Baltimore got a Super Bass I could try? Preferably JMP era?

If I got a chance to play my friends JMP 2203 again, how similar would the tone be?