Fiberboard in Plexi build - But,

[pjd3]

Good lord what have I done.

OK. So planning Sluckys's Plexi build. I get a Fiberboard from Amplified parts because I also want to make an eyelet board from scratch, seems like a fun and industrious thing to do. I marked out all the places where the eyelets will be. Meanwhile, I come across an interesting thread somewhere from some fella reading .4 volts on and eyelet that is connected to nothing (but in close proximity to the V1 plate B+) . While reading through this interesting post on historical issues with Fiberboards and stray conductance, it occurs to me that I created the markings on the fiberboard by drawing out a grid on the board using a .5mm Pentel lead pencil. I grabbed my old Radio Shack VOM and measured the resistance between an 1/8" or so of pencil lead (graphite?). I was getting readings between 1.6 and 16 ohms.

Have I just inadvertantly impregnated my fiberboard with eyelet to eyelet conductors? I've been frantically erasing the grid that ultimately connects all eyelets to every other eyelet on the board. Ha, I don't know what to do. Will erasing hard enough remove enough of that conductive pencil? Is there a cleaner solution that can non-conductively remove this from the board? I just don't know know. What a tragedy it would be to finally come to the end of this and find out my fiberboard is a hyper matrix of conductive highways that leave and arrive everywhere.

I need to go to bed. Wish I had thought of this a little earlier on. Damn green newbies.

Thanks guys, perspectives welcome.

Phil D.

[pjd3]

I just watched a you tube video where a guy was testing if a 2 inch section of a standard "lead" pencil will conduct electricity. He had a 9 volt battery and some kind of LED belt. He snagged the section of lead pencil with the alligator clip, placed the lead section in series with the circuit and the LED belt lit up like 12 midnight on Christmas eve. I believe if I were to go forward with using that board, my amp would detonate like a pipe bomb upon the flip of the switch. I will however drill tiny holes in all the marked positions, clean the sh** out of the board and use it as a template. It was all a good practice in eyelet layout at least from a graphic standpoint, and I practiced doing a small handful of staking eyelets. I did get something out of it all.

anyone want to buy a Plexi board.? kee hee.

Phil D.

[sluckey]

Throw that board away! There is no need to write/draw anything on the board when you use one of my layouts. Just print the drill guide and tape it to the board. Instructions are on the drill guide page. I don't care for that thin fiberboard either. I use only 1/8" G10 fiberglass board.

[pompeiisneaks]

agreed, I tried drilling the fiberboard once and hated the experience so much I just switched to the G10/FR4 garolite and have been happy. Just make sure to wear breathing protection when drilling as the glass fibers go airborne and will ruin your lungs.

~Phil

[pjd3]

Thanks guys, I'm tossing the board overboard.

I don't mind at all using fiberboard, and being laid off from work last week inspired a less expensive approach. ( I got another job already).
Since this is a Bogner Alchemist gut/overhaul I used your layout but stretched the width to 9" vs 6 7/8" to match the pot holes and to allow a tad more space on the board. That's why I used a graphical technique on the board. Forgot I was dealing with high voltages and conductive pencils for the 2 hours it took me to do it. shucks.

Maybe I'll consider going the garolite/turret method for Marshall builds since I'm back to work. We'll see.

thanks for your feedback guys!

Phil D

[Tony Bones]

Using fiberboard instead of FR4 or garolite to build a board is like using leather brake pads in your car. It makes sense only if you have a really good reason to be historically accurate.

[pjd3]

"and being laid off from work last week inspired a less expensive approach."

Being the sole income with 5 dependants at home was really the reason for a $1.97 fiberboard and $8 staking tool. If gigging wasn't a source of income for us I wouldn't have had any reason to get anything but I am very interested in the turret/garolite method. It does appear to be better in many ways and it even looks nice. I have no choice but to seriously consider gathering tools and material for this build.

Phil D. (the king of fiberboard failure - 2019)

[pompeiisneaks]

Perfectly understandable, most of us here are just agreeing that if feasible, the garolite approach is superior. You have to work within your specific allowances.

It will still work.

~Phil

[pjd3]

Thank you Pomp, and as a matter of fact I did grab another blank fiberboard I had and go for a layout. It actually came out pretty good for a first homemade eyelet board. Just hopefully it won't be one of those problematic ones. And I'll keep it dry. No moist hot basements or attics for this "Plexi".

Hey Pomp (or Sluckey, since I'm doing your cool Plexi), I'm having trouble identifying a source for the choke used in Sluckeys Plexi schematic. I even have searched by specs and I'm not coming up with anything I can confidently put on the order list.
Its calling out 14H with a DCR of 487 ohms. Just ain't finding it. If you could suggest a range of feasible chokes for this circuit that would be very helpful.

Thanks guys!

Phil D.

[pompeiisneaks]

Mine was whatever came in the vox. If you're trying for that exact value, you may need to call someone like hammond and ask if they can wind a custom one for you, but that gets costly.

I don't see why something like this won't work just fine:
https://www.tubesandmore.com/products/f ... ent-jcm800

~Phil

[sluckey]

I used a Hammond AO-43 amp as a donor for my Plexi6V6. The choke I used came out if that. I would not focus on the parameters of that particular choke. If I had to buy one I'd just get the common small Fender choke.

https://www.tubesandmore.com/products/f ... e-vibrolux

[pdf64]

Here’s a thread over on TGP where black fibreboard from a reputable USA vendor (Marsh) was so conductive that the mains fuse was blowing. To top it off, Marsh refused to replace / refund
https://www.thegearpage.net/board/index ... t-26345438

[pjd3]

The info I have on the choke that is on the Alchemist chassis is:

5 Henry's @ 1KHz 1v 0mA - thats what is on the BOM

And I measured 46 ohms as the dc resistance.

is there any reason to think this one wont work with the power supply in Sluckeys 6V6 Plexi amp?

I haven't as yet got back to the place where I have a good intuition on what choke specs will work with a certain circuit. I'm only under the assumption that the choke is to filter out high frequency stuff that would otherwise get to the tube plates.

Thanks!
Phil D.

[sluckey]

The BOM specs on your Alchemist choke don't make sense. Post a schematic and we will be in a better position to say if the choke is usable in the 6V6plexi.

[pjd3]

I've actually been looking at the "schematic" for 20 minutes and can't find the choke.

The schematic is broken up into about 12 pages in the service manual. I dont believe anyone has ever had a unified schematic of that amp. There are about 6 boards that are interconnected with many molex connectors and cables. I'm still looking.

Thanks,
Phil d