PRRI + Mojotone small parts kit = ???

Gswearengin

Member
Messages
710
Hey y’all,

I am not even finished tweaking my 5E3 kit yet, but I have the amp building bug and want to do another one...

I have a PRRI that I am pretty happy with. Mojotone sells a small parts kit that could potentially be a cost-effective way to convert it to a handwired amp as my next project. I have seen people say it’s a direct fit, but then I found people saying it’s not so easy. Does anyone have any experience doing this?

Another idea would be to just sell the PRRI and get a Mojotone deluxe reverb kit. This way I get an amp upgrade, pine cabinet, and don’t have to sacrifice a perfectly fine amp and kill its resale value. I definitely don’t need the extra power, but find myself lusting over the deluxe anyway. I also like that it is a “purer” blackface AB763 circuit. I’m in Germany, and the prices of the US made Fender stuff are so ridiculous that I could probably do the whole thing cost neutral, even after crazy international shipping and possible customs fees...and also still cheaper than TAD.

I realize both of these projects are much more difficult than a 5E3, but last time I looked at the PRRI chassis it seemed massive...the 5E3 seemed like a ship in a bottle by comparison...

Anyway, anybody got any experiences, thoughts, or recommendations?

Thanks,

Gary
 

gtrbarbarian

Gold Supporting Member
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2,078
5E3 is a complexity of say 3 on a scale of 10.
A princeton reverb is -one channel- with verb and vibrato...complexity of maybe 6 out of 10.
A blackface deluxe reverb is two channels... about a 9 out of 10.

It's not the building that is the hard part for a beginner, it's the debugging when things go south. I built a signal probe for tracing signal that I used before owning an oscilloscope...but you need to know how to safely and accurately trace signal through a circuit. I think a deluxe reverb would be a bear for you if you're just starting...
Plus there is learning how to build a successful grounding scheme and also perform correct lead dress so you're not hearing gobs of 60 cycle hummmmm....also , soldering...it's going to be bad on your first couple of builds...

Just a learning curve...as weber says, accurately, 'these aren't lego sets'


I'd suggest getting the small kit from mojo, since you have everything else (trannies, cab, speaker, etc).

I'd save a 2 channel blackface for when you have built the 5e3 and princeton successfully...
 

ripple

With Kung Fu Grip and Lifelike Hair
Gold Supporting Member
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3,549
One thing to note is Mojotone kits only come with a layout drawing and a schematic... both in B&W. No real instructions per se, so you have to be able to build it from a (not so detailed) picture.

I'm not bagging on them, mind you: I built a Mojotone JTM-45 kit and LOVE it. I gig it regularly and it never disappoints. It was a lot of fun to build, but considerably easier to build than a Deluxe Reverb.
 

HotBluePlates

Member
Messages
13,903
... Another idea would be to just sell the PRRI and get a Mojotone deluxe reverb kit. This way I get an amp upgrade, pine cabinet, and don’t have to sacrifice a perfectly fine amp and kill its resale value. I definitely don’t need the extra power, but find myself lusting over the deluxe anyway. I also like that it is a “purer” blackface AB763 circuit. I’m in Germany, and the prices of the US made Fender stuff are so ridiculous that I could probably do the whole thing cost neutral, even after crazy international shipping and possible customs fees...and also still cheaper than TAD. ...

I would likely go this route. The Deluxe Reverb has a better phase inverter than the Princeton Reverb (even though I love both amps, for different things), so if you're ever able to crank the DR up to output tube distortion it will be much better.

Also, nothing is ever "easy, direct fit" in converting a pub amp into a handwired amp.

5E3 is a complexity of say 3 on a scale of 10.
A princeton reverb is -one channel- with verb and vibrato...complexity of maybe 6 out of 10.
A blackface deluxe reverb is two channels... about a 9 out of 10. ...

I disagree, in that the Deluxe Reverb is no more-complex to build than the Princeton Reverb; there's just an extra channel. And while there's "more stuff" in the "_____ Reverb" amps, there's a whole lot more chassis room so it's easier to get in there & wire things up without burning parts/wires.

If the 5E3 Deluxe is 3/10, a Deluxe Reverb is no worse than 5/10. There are way tougher things you could be assembling than a blackface Fender amp.
 

rumbletone

Silver Supporting Member
Messages
8,158
I built a Mojotone Princeton Reverb in January.

If i did it again, I’d likely do the Princeton chassis/cab but with BFDR PT and OT and build the circuit closer to a BFDR so I get breakup less like the stock Princeton and more like the BFDR. Though unless a tube is added I’d likely sacrifice the Princeton trem circuit to change it to a LTPPI rather than the stock Princeton cathodyne phase inverter.
 

fiveightandten

Silver Supporting Member
Messages
6,162
IMO, building an amp from scratch is easier than gutting a PCB amp to convert it to hand wired. That's a somewhat thankless task. It won't change the sound much, and if you're a beginner, it's not going to increase the reliability. It'll still have the same transformers, and those are what matters the most.

If you want that amp to sound better, replace the iron with something higher quality. If you want the satisfaction of building something, build something. I wouldn't gut an amp unless you're really on a budget and can't afford the parts for a full amp.
 

Bucksears

Gold Supporting Member
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9,299
One thing to note is Mojotone kits only come with a layout drawing and a schematic... both in B&W. No real instructions per se, so you have to be able to build it from a (not so detailed) picture.

https://www.stewmac.com/How-To/Onli...its/65_P-Reverb_15W_Amp_Kit_Instructions.html

I firmly believe (because StewMac already sells a few Mojotone items) that they're reselling Mojotone amp kits as well. BUT....I think StewMac is writing up actual step-by-step instructions for them, which is the real benefit.
If Mojotone had a walk-through like that for EVERY KIT, they'd sell a ton of them.
 

Gswearengin

Member
Messages
710
One thing to note is Mojotone kits only come with a layout drawing and a schematic... both in B&W. No real instructions per se, so you have to be able to build it from a (not so detailed) picture.

When I was looking for tweed kits, someone (@Bucksears?!?!) pointed out that the StewMac kits are probably repackaged Mojotone kits with full instructions.

There were some minor differences in the grounding schemes, but that’s not uncommon. I used the StewMac instructions for my 5E3 build and it was perfect...made the whole thing way less intimidating, and the process went well.

I’ve already saved the instructions for the StewMac Princeton Reverb and Deluxe Reverb kits, just in case they catch on and take them down. :)

Gary
 

Gswearengin

Member
Messages
710
Sounds like most people recommend building a deluxe kit from scratch, which would probably be my preference. At the end, I get an upgraded amp that I built from the ground up by myself. I would probably fit it with an Eminence Maverick to keep the volume reasonable.

I agree with @gtrbarbarian that there is a lot that can go wrong, and that as a novice troubleshooting is difficult. @HotBluePlates helped me quite a bit with my 5E3 build. I do think a deluxe build is probably not much more difficult than a princeton, there’s just a lot more of it.

Anyway, I realize that it probably won’t be perfect on the first attempt, but there’s no reason a handwired kit can’t be a lifelong tweaker project. The big stuff is good and hard to mess up, everything else is pretty cheap and fun to experiment with! I already from time to time think about totally rewiring my 5E3 to try to make it even better. Unfortunately I found better pictures of what it could look like after I finished the build. :)

Thanks,

Gary
 

gtrbarbarian

Gold Supporting Member
Messages
2,078
Yes..I'll still stick with a black face two channel being more complex than a Princeton...Princeton vibrato is bias modulating...a simpler circuit than the optoresistor type ...plus the different gain stages per channel..and the two channels being out of phase. Lots of stuff to go wrong for. A. Beginner. And if they don't know how to trace a signal or how amps in general work, they could very easily end up with a doorstop that many techs would be weary to try to get working...since by definition, the amp in question has never worked properly.

Guess how I know that? I built a Marshall successfully, then I built a Weber 6a20hp unsuccessfully....and it sat for a year while I learned my way around amps , an audio signal probe and then an oscilloscope...

But hey man that's just like my opinion man...OP can do whatever pleases them.

For the OP I suggest looking up Bill M audio on YouTube..he has a couple of videos on building an audio signal probe, and how to use it to trace signal. This will be invaluable if you don't own an oscilloscope. Good luck
 

Gswearengin

Member
Messages
710
I think it will be a good 6-8 months before I do anything (plan is to take advantage of Mojotone’s Black Friday sale, which is what I did with my 5E3 kit). In the meantime, I will continue to tweak my 5E3...

I put a lot of faith in StewMac’s instructions. They rate the 5E3 2 out of 5/8 hours, the Princeton 3/12 hours, and the Deluxe 4/16 hours. I probably spent more than 16 hours on my 5E3 kit. :) But I was scared of it, and it worked out...I went slowly, followed the instructions carefully, and built it stock first. Now I feel pretty comfortable working on it and have done a few minor mods. I would do the same with an AB763 kit, but I’m pretty confident that I could do it...with Stewart MacDonald holding my hand. They also have a little bit of testing and troubleshooting information.

Thanks,

Gary
 

billyguitar

Member
Messages
5,918
I had a electronically boogered old PR. Scratched off serial number and wrong transformer. I had a guy I know gut it out and rebuild it to a single channel Deluxe reverb circuit. Big improvement in tone. Big Fender sound in a small cabinet. Not what the thread is about exactly but if you could build a PR circuit you could do a DR circuit.
 

Webfoot

Silver Supporting Member
Messages
2,924
I am intrigued by their deluxe reverb kit. Much cheaper than Fenders hardwired 64 and the Mojotone may sound better. Plus you could plan in advance adding mods like switch for negative feedback and changing cap for bassman tone stack mod etc.
 

HotBluePlates

Member
Messages
13,903

The new caps may not easily fit in the space (or through the holes) used by the original caps.

And that kits does not include the filter caps (though does have a bias filter cap); those filter caps oughta be replaced if you're in there swapping parts.

Though audible differences would be small, some detective work shows Mojo would be selling you the large polypropylene orange drop caps, and I'd expect polyester caps (whether orange drops or some other type) to sound slightly warmer (again, if there is any tonal difference).

... Difficulty? ...

You're gonna have to get inside the amp and un-hook the main board from the pot board, so you can get at the underside to unsolder/replace the caps. So it will be a fair amount of hassle.
 
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Gswearengin

Member
Messages
710
The OD caps that came with my 5E3 kit were 715’s...so pretty standard, not the premium ones. I used Mallory 150’s for that build, but would stick with the Orange Drops for the AB763 build.

My memory from looking at the circuit board of my PRRI is that I would not want to have to work on it! The components are pretty small, I don’t think the Mojotone cap upgrade kit would be realistic. Could be wrong though!

Gary
 

HotBluePlates

Member
Messages
13,903
The OD caps that came with my 5E3 kit were 715’s...so pretty standard, not the premium ones. I used Mallory 150’s for that build, but would stick with the Orange Drops for the AB763 build. ...

715P are polypropylene orange drops. 716P are the same cap, but with tinned copper leads.

225P are polyester orange drops, and like all polyester dielectric caps are quite a bit smaller for the same capacitance/voltage.

The "PS" type orange drops ("2PS," "4PS," or "6PS") are polyester in ratings up to 1kV, and polypropylene from ratings above 1600v.

The primary advantage of "premium" copper lead units is if a circuit experienced problems due to magnetic fields inducing current in the caps' leads. The orange drop caps without copper leads use tinned steel leads. FWIW, I've never noticed any difference, so the benefit seems mostly psychological.
 

HotBluePlates

Member
Messages
13,903
... Seriously, I’ve only seen PS>225>716>715. I’ve never actually seen anyone explain what the differences are.

The PS series & 225 series are "all the same" to me. Ditto for the 715P & 716P series.

Sometimes, in some amps, I feel I hear a slightly warmer sound out of polyester dielectric and a slightly wider-range, pseudo-hi-fi sound from polypropylene. It hasn't been a consistent impression to me all the time, but on occasion I'll choose polyester dielectric caps for that reason. FWIW, when you see things like "the old blue molded Ajax caps in Fender amps are Mylar," know that "mylar" was the DuPont trademark for a polyester film.
  • So maybe 10-20% of the time I hear a sonic difference worth choosing one cap dielectric type over another.
  • 100% of the time polypropylene caps are bigger than polyester for the same capacitance/voltage.
  • 85-95% of the time, guys will swear one cap is so much better than another.
  • When I sold stuff I built, I offered a choice of cap types because of the buyer's existing bias (and not based on which type I felt would sound best and offer the best value) 100% of the time.
Most of the time when building something for myself, I'll build with a polyester dielectric cap because it sounds good, takes up less space, and very often costs less.
 




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