Scratch building a version of a Ceriatone Plexi 51 All Access

Finished a few other tasks today. Decided that I didn't like the Presence caps so I reworked those. Added V2 10K dropping resistor, and the output jacks.

The thing with building from scratch is getting everything to fit, footprint wise. I knew when I drilled out all the holes that everything would fit, as I did several mockups to ensure fit. Then today when I mounted the output jacks, the switch for the NFB wouldn't fit, until I remembered that the jacks needed to be flipped over 180 degrees to fit properly. Duh !

I'm about at the point where I need to finish up the bias circuit, trim pot, and meter jacks or order the back plate and wait.



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I have slowed way down on the Plexi 51 build since the last update due to needing to have the face/rear plates made before continuing on to finish up the remote bias. I'm not ready to place the order yet to Sandy at Precision Design to make the plates, as I have another previous build that also needs plates, and I'm in the chassis drilling stages for another new build that I have not tried before that will need plates too. I'd rather pay her one art/layout fee to design the 6 plates needed, and that adds up a bit and I'm short on coin at the moment. I have however finished mounting/wiring the Granger FX loop board and the imp. / selector switch on the 51.

I won't mention all of the details yet on the new build, not in this thread, other than the new amp design will be built off of a PCB (that is a first time for me), and it will be a joint - built amp when finished, built in co-ordination with another well known builder. I'll build the base amp complete and playable, then will ship the amp to the other builder who will apply his high gain screaming mods. This is a one off design and I'm only working on the new build because I have almost all of the components here for the 14 watt amp. Hope I didn't reveal too much.
 
So this build has been side lined on the shelf for over 6 months and I'm about ready to fire it up. After thinking about what I had originally started, I decided to change horses in the middle of the stream, so out came the original board and I removed a lot, well most everything an started over, so here is the new turretboard.







 
I decided this version would be a fair likeness to the JTM45, the JTM Black Flag, the 1967 Plexi, and the 1968 Plexi. And with tube changes and rebiasing I think it will do a fair like ness of a 1959 Fender Tweed Bassman. Since there is no practical way to include all of those years in one amp because of the differences in iron and filtering I decided to go with tube rectification, which isn't correct for the plexis, and I am going with EL34 tubes, and have 6L6's to try in it too for the JTM45. Filtering is the Black Flag version which is close to the JTM45 except the preamp cap.

This amp features correct preamp, tonestack, and mixing resistors for each period. All are switchable. I stayed with the PI coupling cap values of the JTM period, the .1uF's.

So to sum it up:

it does the JTM45 period correct without the KT66's with EL34's instead.
it does the Black Flag correct with the EL34's.
It does a 1967 version correct but with tube rectification and the filtering slightly off
and it does the 1968 version correct but with tube rectification and the filtering slightly off
 
Not sure where it goes, all I know is two times building from scratch is "enough". It's a Bitch trying to figure out what to keep in and what has to go. And that is a lot of layering to build, then tear out and rebuild better. The jumpers connecting the bypass switch to the FX board alone took 3 hours to bend and hold in place to solder.

But I really like this version, and so far I think it turned out exactly as planned.
 
syscokid said:
Is that preamp filter cap zip-tied to the board?
Click to expand...


Yes. I didn't want the cap to wiggle. I used the normally unused portion of the second can cap for the CF, which allowed me to only need one more filter reservoir cap for the preamp. I guess I could goop it, but am not much on that except when I absolutely have to
 
Mini switch functions:

Split /shared V1 cathode

Tone Stack swap from JTM values 56K slope +250pF Treble to Plexi values 33K slope +500pF values

Bright channel Bright cap selection switch 100pF or 500pF

V1B Plexi mode cap selection from .022uF to .0022uF

V2A Plexi mode "Fat Switch" / cathode .68uF bypass

ERA switch for swapping mixing resistors from 270K to 470K

NFB switch to change the NFB resistor from JTM 27K to Plexi 47K



No PPIMV, No Half Power Pentode to Triode, and no Rectifier Selection between S.S. or Tube, Tube only

A JH attenuator will be built and included for sole use on this amp instead of the PPIMV and Half Power
 
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