1959/2204/SIR #39 three in one

[romberg]

Here is a little 50 watter I built that has a preamp that is configuable as either a 1959, 2204 or SIR #39. The 1959 setup has a bright and dark channel that are internally jumpered. The 2204 and SIR share a seperate gain control. Switching is done via either a panel mounted rotary switch or a foot switch.

Sound clips: https://www.youtube.com/watch?v=JxbR919Bn-4

Build PICS: http://home.comcast.net/~mike.romberg/amps/cerberus/

[Thiez]

Nice build, i've got something planned like this for my own build. At the moment it's a superlead with PPIMV, but the mods for 2204 is lying around waiting to get build in. Since i have a gainstage spare, i had plans to mod in a SIR stage.

You did any mods or changes to the circuits? What brightcap etc are you using?

[romberg]

Thanks! It was fun to build. I've always been meaning to build a Marshall. Just couldn't decide on which one. When I saw this idea in the SIR thread, the decision was made.

You did any mods or changes to the circuits? What brightcap etc are you using?

There are schematics and a layout linked on the pictures page. Here they are:

preamp: http://home.comcast.net/~mike.romberg/a ... preamp.pdf

power supply/amp: http://home.comcast.net/~mike.romberg/a ... /power.pdf

layout: http://home.comcast.net/~mike.romberg/a ... layout.pdf

I did sit down and compare the preamp component values to a 1959 and 2204 schematic. And they matched. The power supply is 2204. I'm not a Marshall historian. So, I don't really know which exact versions of these circuits I recreated. The voltages are a bit high as I think the transformer I used is an accurate copy and is wound for 110V mains. For the SIR stage, I made an educated guess based on information around the net.

No real signal related mods other than a PPIVMV. I did add Merlin's arc protection to the cathode follower and a couple of bleeder resistors to the power supply. The bias supply is powered when the mains switch engages and I added 1 ohm resistors to the power tubes with external test points. Finally there is a 4.7M grid leak on the gain stage before the cathode follower to prevent pops when the relay switches.

Mike

[neikeel]

That's really neat Mike.

thank you for sharing, I made similar 100w but used ABY to switch between modes and a push pull switch for boost, yours is much neater and well executed.

[Thiez]

Verry nice schematics mike! And with that said, i also complimented myself haha Our schematics are very much alike, only mine is a plexi based with 4 holes still. Also added jose master (still not sure if it will stay) and a resonance mod.


I planned my build in seperate parts, first the superlead with PPIMV (where it is now) and then mod in the other things. Only i have to find the time for it..... Here's my schem: https://db.tt/asIh1wTi

[dnkhoward2]

Here is a little 50 watter I built that has a preamp that is configuable as either a 1959, 2204 or SIR #39. The 1959 setup has a bright and dark channel that are internally jumpered. The 2204 and SIR share a seperate gain control. Switching is done via either a panel mounted rotary switch or a foot switch.

Sound clips: https://www.youtube.com/watch?v=JxbR919Bn-4

Build PICS: http://home.comcast.net/~mike.romberg/amps/cerberus/

Nice tone and versatility romberg. Thanks for sharing!

[jasonvilla]

Does anyone know if romberg's schematics are still hosted somewhere? Those links don't work for me.
Thanks!

[romberg]

Does anyone know if romberg's schematics are still hosted somewhere? Those links don't work for me.

Yea. My "beloved" comcast, in it's race to the bottom, decided to remove personal web pages. The drawing can be found on the ampgarage. But since that site is using some ancient version of php that has apparently been infected with malware you may only wanna go here if you use something sane like linux/bsd:

http://ampgarage.com/forum/viewtopic.php?t=25084

I've created a github repository that holds the schematics and layout (I've included the kicad and librecad files along with the pdfs). You can find them on github here:

https://github.com/mromberg/cerberus

Mike