Mojotone Princeton Reverb Kit Using Hoffman Board

[sec1rlr]

Newbie here and my first post. I'm learning.
I just purchased a Mojotone Princeton Reverb Kit (haven't even received it yet). I want to use a Hoffman Style Turret Board - looks better, cleaner, stronger, just personal taste, etcetera.
I studied how to use the DIYLC app to lay them out and have them built. I saw Rob Robinettes files and I understand if I had the DIYLC files I could import them and have it created. I've also read where others like me have had a similar interest in using a Hoffman Terret board with the mojotone kit. Trouble is,.. I can't seem to find any existing DIYLC file layouts that are specifically labeled for the Mojotone Princeton Reverb Build and I can't alter any existing one or create a new one since I haven't received the eyelet board one in the kit yet. I'm thinking there are some slight differences between the Princeton Boards I've seen on the site vs the actual one included in the kit in terms of component dimensions. Hope this all makes sense.
Any suggestions or comments? Any place to find DIYLC files specific to the Mojotone Princeton Reverb? Does one of the existing layouts work without any modification? I appreciate you sharing your comments and suggestions.

[EL34]

Posted in the wrong board, moving....................

[SEL49]

Mojotone and Robinette both used the original Fender layout so their boards are almost identical. Mojo's board will not require any drilling to fit Mojo's chassis. Rob's board will work just fine in the Mojo chassis but you will likely need to drill new mounting holes.  Rob's DIYLC full layout is on his website and Hoffman already has Rob's DIYLC board only layout, so Hoffman can easily make Rob's board for you. All of Hoffman's boards are 3-1/8" wide so you will have to drill new mounting holes.

Also consider... Hoffman has a completely different board layout (and documentation) that will work in the Mojo chassis. Hoffman's documentation is not a simple "paint by numbers" scheme so you will need some basic electronics skills. Hoffman's board is my preference. It also includes an onboard bias pot.

If you decide on Mojo's layout then use Mojo's documentation ONLY. If you decide to use Hoffman's board then use Hoffman's documentation ONLY.   

***DO NOT MIX AND MATCH THE TWO DIFFERENT DOCUMENTATIONS***

One more thing... The boards that come with Mojo's kit are thin flypaper material. Any board made by Hoffman will be 1/8" thick fiberglass material.

[sec1rlr]

Thank you for the detailed reply. I compared the "small parts" kit items from Mojotone with Hoffman's partslist and there were only a few differences in terms of needed capacitors and resistors, etcetera. The point being I could use a majority of the Mojotone kit stuff to complete the Hoffman build.
I'm curious, you said you would complete the Hoffman build over the Mojotone build. Can you elaborate? Why would you choose one over the other given a turret board could be used with both builds. I do realized Hoffman's build included the pot bias functionality but this could be added to the Mojotone build. Was there something specific that made you prefer the Hoffman build?
As always, thank you for your comments. I do learn from them.

[mresistor]

Consider that the Hoffman board component spacing is smaller than fender/mojo/rob spacing.  I have used several Hoffman PR turret boards and I almost always use the smaller sized xicon polypropylene radial capacitors (or similar) or orange drop radials.  If you are wanting to use jupiters/mallorys/sozo axial capacitors the traditional Fender layout will be much easier for you to mount the caps.


Hoffmans layouts can be modified to adjust distances in component spacing but maybe that is a bit much for someont to do that hasn't done much turret board building and laying out varying from the instructions and examples. I don't think its something you want to do just starting out in amp building.


The mounting thing is really not a big deal. If you want to used the standard fender layout then the holes are probably predrilled for you in the Mojo chassis. If you decide to use a Hoffman PR board then like SEL mentioned you will have to drill a couple of mounting holes.


If I were you I'd build the MOJO kit with their eyelet board. If you want to use a 1/8" thick FR4/G10 board with a traditional Fender layout then just wait for your eyelet board to come and then use it as a mask to locate all the turret holes on the new board. You will have to oder board from some other vender if you want it wider than 3 1/8".  I sourced a bunch of FR4/G10 on ebay that was much wider. Many people order whole sheets of the stuff. Be advised it is a pia to cut and makes a lot of sticky dust and you need a table saw usually. You will need the Keystone turrets and I suggest use Hoffman's, and you will need to tools to stake them on the board. I use a drill press for that. 


I wouldn't think eyelet boards with the insulating backing board aren't nice to use.  Thousands of them are still working fine in Fender amps from the 50s 60s 70s.


You can order a Hoffman PR board here with the turrets already mounted.

[mresistor]

Amending what I said.  I just looked at the MOJO AA1164 PR vulcanized eyelet board. It has all the underboard holes drilled on it.  If you use it as a mask to layout a turet board you will have to identify which holes are under board wire routing holes and if you want them or not. Those under board holes and board mounting holes are larger so not so hard to determing which holes are which.  Use a fender AA1164 layout diagram too. On the AA1164 Fender original layout there are quite a few under board wires. IMO many are not necessary, especially with a turrent board. However aesthetics come into play with wiring and a board will look prettier with underboard wiring employed. With turrets when a lead comes to a turret from under the board you will want to bring it up from underneath and then make a hook over the top of the turret to make sure that that underboard wire never falls out of the turret underneath the board.

[mresistor]

Also I'd wait for the entire kit to arrive before proceeding and see what ya got before making any decisions. Although I understand planning is good it might have been better to ask some questions before ordering an entire kit. There are other options for PR chassis and iron available, maybe you were aware.

But now you have a kit coming. 

[TitaniumValhalla]

I don't necessarily have a definitive answer but here are a few observations. Comparing the Hoffman layout and Mojotone, if you are expecting to use components that came with the Mojotone kit and have them fit directly onto the Hoffman board, you may have issues - the Hoffman board is more compact in some areas, and some larger components may either not fit or may interfere with other components due to their size. When Mojotone designed their kit they worked all that out for their board. It's not an insurmountable issue but just bear it in mind, you might find yourself ordering some additional parts here or there as a result before you are finished if you decide to use the Hoffman layout using the Mojotone supplied components.

The Hoffman layout incorporates some common-sense improvements to the circuit - 1 ohm bias measuring resistors and bias adjustment pot, shielded input wire, screen resistors, etc. whereas the Mojotone layout is pretty true to the original. Unless you want to mimic the original layout for appearance's sake, Hoffman's is "better".

I would reiterate the earlier caution that whichever you choose, STICK TO IT and don't mix them. If you are not an experienced builder, stick to the known layout exactly and you should have good results. You can always mod after the fact, but that is much easier as a newbie if you are starting from a known working amp rather than trying to troubleshoot a new build that isn't working when you made changes to the layout in the process. Just check out the many pages of threads from others trying to solve issues with their new builds when they mixed/matched ideas from different layouts, adding mods sometimes incorrectly in the process, while still trying to learn best practices for soldering, lead dress, grounding, etc. Best thing you can do is make the decision on the known layout you are going to use and then follow it religiously. Neither Hoffman nor Mojotone will steer you wrong if you do. Good luck.

[Willabe]

One more thing... The boards that come with Mojo's kit are thin flypaper material. Any board made by Hoffman will be 1/8" thick fiberglass material.

That above is a big thing, it's a deal breaker for me. ^^^^^^

No way would I use a thin vulcanized fiber board. I wouldn't even use vulcanized fiber board even if it was thick. They lead to problems down the line.

We have wonderful dependable fiberglass boards now.

The spacing with Hoffman boards, I would figure out what coupling caps I was going to use, buy them, measure them, then use Doug's board design and lay it out myself. Then have Doug make it.

Some guys love the sound of them and their small size, but I don't like those Xicon polypropylene capacitor for the coupling caps, too clean sounding.

[mresistor]

Willabe  In my experience servicing many old Fender amps I have not run into any fibreboard that has had a conductive problem. And they have been 40-60 years old.  I have run into several thinner fiberglass/epoxy boards that were conductive.  Vox and Marshall, granted they were MIC.  have read that there were some CBS boards that became conductive and one theory was it was because of the wax like coating the put on them.  Of course the fiberboard could be more suseptive to moisture intrusion but who knows for sure. Ive had amps here that were underwater for a time and the boards were just fine. A Super Reverb from Texas Comes to mind, guess you could call that one the Texas Flood amp. It's still going strong today, with a new cabinet, speakers, reverb tank and cables. Just my experience  and of course everones mileage and experience is different. Are there any scientific studies that have been made on the durability of vulcanized fiberboard, because there are many other places where they are used as insulators not just guitar amps?


IMHO the newly manfactured vulcanized fiberboard is going to remain serviceable for a good long time, decades.  However it comes to mind you might be talking about some other problem with fiberboard eyelet boards.


Of course modern FR4/G10 is a very good insulator and material to use. No one can debate that.

[Willabe]

In my experience servicing many old Fender amps I have not run into any fibreboard that has had a conductive problem.

We have seen it  many  times here. It was already known back in the 90's when the vintage amp thing happened it was a well known and documented thing. I've been here for ~15 years, have read almost every post since then, I read all of Kevin O'Connor's web forum when it was around, many tube books. They all confirm the same thing, that many/most of those Fender boards go wonkey sooner or latter.

My BF SR, I had taken the boards screws out, was playing through the amp, and with a plastic screw driver I would push down on the board to get it to make solid contact with the chassis. The sound got way thinner, less fullness, with a little less volume. But I was used to my amp sounding like that. I had very little tube amp experience then, so I left it. Now I'd change that board out in a heart beat. 

So it can be, often is, effecting the amps sound, but the amp still seems to be working fine.   

I think that happens to lots of Fender amps, but you don't hear it because it happens slowly. But it's there. With a fiberglass boards that won't happen.

I have run into several thinner fiberglass/epoxy boards that were conductive. Vox and Marshall, granted they were MIC.

I've only heard of this 1 time. Silvergun had a new black fiberglass board that was conductive.

They do make conductive fiberglass boards, not sure why, but they do make them.   

have read that there were some CBS boards that became conductive and one theory was it was because of the wax like coating the put on them.

Well, the boards before they waxed them were having problems with moisture and becoming conductive.

The theory was that it was proof the Fender was aware that the boards went conductive over time and that's why later boards were dipped in wax to stop them from absorbing moisture and going conductive. Fender would not take the time and spend the money to do that if they didn't need to fix a problem. 

Of course the fiberboard could be more suseptive to moisture intrusion but who knows for sure.

See above.

We do know for sure, we have empirical evidence, from many examples, that some/many of those boards do/did absorb moisture.

Ive had amps here that were underwater for a time and the boards were just fine.

Sometimes the board can be dried out and will work fine, sometimes goes wonky again. Some guys take out the board and bake it in an oven or small toaster oven at a very low temp to dry it out. Sometimes it works, sometimes, like above, it just gets bad over time again, few months to a year or so. 

Are there any scientific studies that have been made on the durability of vulcanized fiberboard, because there are many other places where they are used as insulators not just guitar amps?

I have no idea, but like I said above we have a lot of case study examples, empirical evidence, that proves without doubt that it has and still does happen.

IMHO the newly manfactured vulcanized fiberboard is going to remain serviceable for a good long time, decades.  However it comes to mind you might be talking about some other problem with fiberboard eyelet boards.

I'm not talking about some other problem.

Do what ever you want, but we've seen way too many examples that many vulcanized fiberboards most likely will develop problems.   

Yes it takes time, but if I have a reasonably priced option, I'm gonna use it. I wont touch it, if I don't have to.

[mresistor]

Consider   not knowing the exact history of many of these Fender amps that there could be other reasons for the conductivity. And that's not true it can happen with fiberglass boards as I've seen it right here on my bench and just ask the folks at Marshall. 


I won't debate you anymore, it's pointless.

[Willabe]

Consider not knowing the exact history of many of these Fender amps that there could be other reasons for the conductivity.   

I won't debate you anymore, it's pointless.

I'm not debating.

What has "not knowing the exact history of many of these Fender amps" got to do with it? That doesn't change anything. 

Over many years now, it's become very clear by the many examples that vulcanized fiberboard IS problematic in tube amps.

And that's not true it can happen with fiberglass boards as I've seen it right here on my bench and just ask the folks at Marshall.

All I said was I've only heard of it happening 1 time.

And to me all bets are off with anything made in China, which you eluded to also. Who knows how they make things?

25 years back or so China sent over what was supposed to be dry wall and it all had to be taken out because it was bad. It was what they put in the dry wall paste they made the board out of.

Edit; I'm talking 100's of thousands of sheets, whole subdivisions needed to have all the drywall torn out after a year or so with people living in the houses.

[pdf64]

there are many other places where they are used as insulators not just guitar amps

Such as?

[mresistor]

power control and distrubution panels in machinery and electrical equuipment  and isn't it used in pickup bobbins.


PDF64   here is a MIL Specification MIL-I-695A  and this is probably the same or similar to the stuff used in US Military and US Gov systems.  Antique Electronic Supply carries something similar as well. These are grey and some commercially available similar materials are blue or even green. I would like to know who the manufacturer is that is making the current black fiber board and if it still contains cellulose. The one above is using cotton fiber.

[Willabe]

I have run into several thinner fiberglass/epoxy boards that were conductive.  Vox and Marshall, granted they were MIC.

I wonder if it's not the board itself, but left over residue from etching off the copper and then cleaning the board afterwards when they make the pcb traces?

[Willabe]

I have run into several thinner fiberglass/epoxy boards that were conductive.  Vox and Marshall, granted they were MIC.

I wonder if it's not the board itself, but left over residue from etching off the copper and then cleaning the board afterwards when they make the pcb traces?

I asked Doug and he said he's probable sold like some 10,000 fiberglass boards over the last 30 years and has never had 1 complaint that the board went conductive.

[Willabe]

Here's a guy who bought some fiber board from Mojo, said it was conductive from the 1st day.

As some may remember, I had my heart broken several years ago on a DRRI tear down and rebuild when I used Mojotone black fiber board, and had to rip it all out because it was conductive from day one. I said I would never use it again, but I had heard the grey board Traynor used wasn't a problem, and maybe it was the carbon black that was the issue

Gerald Weber also thought it was the carbon black dye that made the Fender boards go conductive. 

On page 2 they discus how to clean a Fender board and if cleaning and/or heat/drying it out will even work. They say it wont. Once it goes conductive it's toast.

Link to thread;

https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/948165-fiber-board-bites-me-in-the-ass-for-the-last-time

[mresistor]

If anyone wants to know the Mojo boards contain cellulose and can absorb moisture over time are manufactured by this company.

[sec1rlr]

Update:
First of all I again want to thank everyone for their comments and insight. I thought I would add an update to my original post to let everyone know my progress and share my thoughts on the build.

I completed the build of my Princeton Reverb clone. I choose to go with the Hoffman build and ordered basically all of the circuit parts from the Hoffman website including the turret board. I also ordered the complete Princeton Reverb Kit from mojotone and thus had access to all of the "hard" parts to use in the build. Why did I go with the Hoffman layout and spend the extra money to insure I had the correct parts for his build layout? Simple really, I wanted what many members on this board viewed as being the "best". My consideration also included the fact that I'm 64 and probably only going to do this once so why not build the "best" that I can build. The added cost was in the range of 175.00 and now I have a lot of capacitors resistors to use in another build should I decide to make one. An extra part of the expense was using a Cap condensor like the one shown in his build pictures, 40, 20, 20 20 vs the one provided in the Mojotone kit at 20,20,20,20. Many commented that I probably wouldn't notice the difference but did add the larger condenser was in theory better.
Now my comments about the actual build. I have never built and amp before and had very little experience at this level of electronics. I've installed a few remote starters on cars so that was about the level of my electronics experience. Considering my lack of knowledge, I spent a lot of time on this forum and YouTube researching stuff to help me get a grasp of the project. Uncle Doug, Hoffman, Stewmac, Mojoton, Psionic and D-Lab Electronics are just a few of the sites and references that come to mind in my research. One thing I did that I think was paramount in helping me to get things right from start was taking all of Hoffman's materials and sending them to Staples for 11x17 color prints. With the schematics, I actually had them laminated so I could make checks and notes on them. Having them in front of me on 11x17 prints helped me to see how Doug had actually made up his Princeton Reverb build.
Another point for someone like me wanting to use the Mojotone kit but the Hoffman board that I want to make is this... Hoffman's board layout is clear if you understand the concepts, but as many has said it is not a "paint by numbers" diagram. For instance, he only shows one input jack, he refers to diagrams on a seperate schematic using terms such as board A, B, C, D if I remember right.  The point is, you are probably going to scratch your head a few times. Another point to keep in mind... while others warned me to stick to the build layout for the board I planned on building; ie, Hoffman Build,... stick to Hoffman schematic... Mojotone Build,... stick to Mojoton schematic, I did in fact reference the Mojotone and Robinette's schematics and written manuals by Mojotone and Stewmac just to get my arms around "how they did it". This helped me understand Hoffman's logic a little better. I was careful to no deviate from Hoffman's circuitry on layout schematic but it did help to see how others did it.
In the end, I'm super happy with the results. It took a lot of hours to do and I learned a tremendous amount. I have the utmost respect for those that understand the underlying logic and the why's of how this all works from an electronics level. I'll try to add a couple pics of my build. Oh... one last thing.. I followed Robinettes guide to initial startup of an amp and yes, I build a light bulb current limiter.
My numbers on the pin 5 of the power tubes where 34.6 and pin 8 bias set at 20ma
If anyone has any final comments or suggestions, in the words of Ross Perot, "I'm all ears". Thanks again everyone.

[sec1rlr]

My build for those that are curious