New Plexi 50 build

[bluestone]

So onto the next build.... I am going to gut one of my 5f6a amps and do a totally new build. I have the required Bassman and AB763 amps so the Fender sounds are covered. I have never owned or played through any  Marshall amps extensively but I would like to cover that sound.

Build limitations: I will be using a 5f6a chassis, Kendrick 2410P PT, choke and Bassman OT, 2-Weber California 12" speakers in a 5E8 tweed cabinet. The filter caps must be put on the inside of the chassis as there will not be clearance for the speaker if they are located in a doghouse type of arrangement.

My thought is to build an extended Plexi 50 Hoffman board, I have one of Doug's aluminum drilling guides, and mount the caps on thePT end. I will be using the SS rectification as on the board layout. My thought is to build a standard board with jumpered inputs through V1 and eliminate 2 inputs. I would probable like to add reverb with the MV shown.

Thoughts??? Ideas??? Layouts!!!

[phsyconoodler]

It will likely sound like a Fender with all that Fender iron and those speakers.
Part of the Marshall sound is the output transformer and the speakers.Weber California's are not going to sound very Marshally at all.
  Nothing beats Celestions when it comes to Marshall sounds.
If you want some Marshall sounds I suggest losing the bassman OT and get some Celestion speakers.
  I proved that with my recent Overdrive Rocket build.I used 6CA7's and a JCM800 OT.It really sounds very Marshally.And a 4-12 cab with greenbacks seal the deal.
  I've built a few of these amps with Fender OT's and even with EL34's they never leave the Fender tone camp by much.
The California Webers are great speakers,but the breakup is out of sync with Marshall. IMHO.

[bluestone]

Good points and not too bad a deal I can get a couple of Greenbacks and a new OT.....

[bluestone]

I am planning out the "Add reverb to a western electric circuit". My thoughts are to use the existing valve chassis holes. Since I will using SS rectification, my plan is to move the power tubes over 1 spot and use a reducer plate for the PI tube giving me the 4 preamp tubes. Good idea????

[tubenit]

The "add reverb to a western circuit" works and sounds good. There are also other "one tube reverbs" out there also. There is some information on those here:

http://www.el34world.com/Forum/index.php?topic=7957.0

This will also work on the Plexi 50w. You can see an example of how to insert it on the Plexi 25w reverb that I built here:

http://s28.photobucket.com/albums/c216/tubenit/?action=view&current=Plexi25RMTS.gif

With respect, Tubenit

[Fresh_Start]

+1 on ditching the Weber California speakers.  I put one in a Blues Jr. and it moved that amp away from whatever shred of Marshall sound it had.

As far as the filter caps go, somewhere in the Library Doug talked about and showed a build with the preamp caps between the board and the pots/ground bus.  I liked that idea and have built two amps (both Blackface Fenders) with the power amp caps at one end of the board and the preamp filter caps on the edge of the board close to their respective circuits.  The preamp ground bus is attached to the board instead of the pots (orange line below).  There is a very short poweramp ground bus too, but otherwise this is darn close to Hoffman's layout style:



On the earlier build, I used radial filter caps for the preamp and that actually worked out better IMHO.

Don't know if that helps at all.

Cheers,

Chip

[bluestone]

Thanks for the replies....That is exactly what I needed...I like the idea of putting the caps in the space between the pots and the board.... Greenbacks and OT will be ordered....Thanks again!!
Tom

[bigdaddy]

2 greenbacks will not handle that amp if you crank it. I agree 100% about the OT and speakers but greenbacks are basically 25 watt speakers at most. I would think that maybe the Eminence versions would be better and cheaper. They have a very similar sound but will take a lot more wattage. Will they sound like greenbacks, not exactly but close, those greenbacks will last a very short time if you crank that amp, especially if you use a lot of lows.

Also adding verb will loose that sound. The true Plexi sound is dry and it sizzles like you just lighted a fuse for a bomb and the sound explodes. People over the years have lost the original sound to the Marshall by adding master volumes and extra gain stages, verb, tremolo and attenuators.

The original Marshall sounds were raw and explosive. Listen to live Cream....that's what a cranked Marshall sounds like.

[bluestone]

I have a barely used pair of Fane Axiom 10" which will handle the wattage but I don't know how they would sound in this circuit...Any thoughts on using them?

[Fresh_Start]

Newbie question here:  if you put two 25 watt speakers in series, do you get 50 watts of capability?

Just wondering if it works like resistors.

Chip

[simonallaway]

As far as I know the power handling of multiple speakers, regardless of series/parallel wiring, is cumulative. So, yes.