Scratch building a version of a Ceriatone Plexi 51 All Access

T-Rex

T-Rex

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I had interest in building a 50watt Plexi project, and like the "swiss army knife" appeal of the Ceriatone Plexi 51 All Access, so I decided to build my own version. For those who haven't looked into the Plexi 51, it is very well built, and for those who want one, the lead time is really long, usually more than 3 months or more. I downloaded the available photos and user manual to better understand all of the available functions.

I decided to toss a couple of functions, add some others, an started rounding up materials. This will not be a quick build, it's as time permits. I need to start off by saying the quality of the Plexi 51 is vastly better than what Nik built a few years ago, and to all the current owners of one, you have a nice amp. With that said, I won't be skimping on any components either, and am using American iron, ClassicTone and Heyboer.

I bought a steel chassis with a slightly bigger footprint than what I normally use, got most all of the components in and started the thinking process
 
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T-Rex said:
I had interest in building a 50watt Plexi project, and like the "swiss army knife" appeal of the Ceriatone Plexi 51 All Access, so I decided to build my own version. For those who haven't looked into the Plexi 51, it is very well built, and for those who want one, the lead time is really long, usually more than 3 months or more. I downloaded the available photos and user manual to better understand all of the available functions.

I decided to toss a couple of functions, add some others, an started rounding up materials. This will not be a quick build, it's as time permits. I need to start off by saying the quality of the Plexi 51 is vastly better than what Nik built a few years ago, and to all the current owners of one, you have a nice amp. With that said, I won't be skimping on any components either, and am using American iron, ClassicTone and Heyboer.

I bought a steel chassis with a slightly bigger footprint than what I normally use, got most all of the components in and started the thinking process
Click to expand...
I am quite impressed that you are using a steel chassis...
The first thing I do is solder all the ground lugs to the chassis (nut bolt and soldered).
It take about 1000 degrees to really solder it to the steel....
(I preheat the chassis with a heat gun 1000 degrees) then use a soldering iron at 450C.
and so that must be done before mounting the transformers or anything else on the chassis.

That's basically the way Fender does it. The ground lugs are soldered to the chassis first.
Then the parts are loaded on.

If it was aluminum, the ground lugs would be heli arced to the chassis first, before mounting the transformers.
Of course there is no way to solder to aluminum.
Aluminum is usable still, if the grounding lugs are welded to the chassis.
But also don't forget how soft aluminum is...

There is a new aluminum alloy, which is 80% less prone to oxidization....
This may be promising for aluminum chassis.
 
I've worked the last couple of weeks on the schematic, and transposed ideas to the layout. Here's what I've come up with for options that cover from a JTM45 to a 2203/04 (inlcuding if I swap some tubes, and rebias, also a 59 Tweed Bassman).

If I list, (same as), then the option on the Ceriatone model stayed as is. The options I intend are:

.Tube Rectifier or S.S. switchable (same as)
. 4 hole input (same as)
. Internal jumpered on a switch instead of push pull--Jumper mode (relatively the same)
. 3 way Bright Cap Switch (same as )
. V1B Cap Switch to .0022uF (same idea, more accurate than the layout shows)
. V2A Cap Bypass switched to only .68uF option (same switch idea, 330uF dropped)
. Tonestack Lift Bypass switch/function gone
. Presence Cap selection switch (same as)
. Split Shared V1 Cathode (same as )
. NFB 3 Way switch , values changed to be more accuarate
. FX loop swapped for a Metro FX Loop
. Plate Voltage test point added to the external bias points
. Tonestack Value Swap switch (same as)
. 1/2 Power Switch gone, in favor of JH style permanent mounted attenuator
. PPIMV gone, Pre PI Marshall Master instead
. V1A Normal Channel Bypass cap now selectable either 3uF or 220uF, ability to cut mud
. ERA switch added to switch blended resistors to 270K from 470K, closer to JTM45 spec
. ERA/PI switch added to switch between .022uf coupling caps to .1uf coupling caps, more JTM45-ish
. Cascade switch added to flip from a Plexi to a 2203/04 preamp spec.

ClassicTone Power PT is a 150mA rated, Heyboer OT is 3.9K rated enabling more possible power tube swaps.
 
More steel drilling of the chassis in the next couple of days for mini switches and mounting the OT and choke.

Then maybe start laying out the final turret locations for the board so I can start drilling the blank board out. With adding the JTM45 to the original options, and adding a true 2203/04 preamp adds a lot of more ideas to the soup.
 
Excellent. My Ceriatone OTS 20 is a great Amp, but I had to have it built for me! Looking forward to the build!
 
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