Going off Grid - Taking a schematic and adding to it

Anyway, due to my inability to realise where a fuse goes, I found myuself with a power transformer (100w) for a mrshall-esqiue style build. I also have had a jtm45 chassis lying around I'd meant to do a boring jtm45 in as a "intrroduction to turret builds" project. However, the jtm45 is a grandpa amp, for people who like blues, strats and ignore massive racism whilst extolling how great Eric Clapton is...
So, it's about time I took something I want to build and add some stuff to it. Going a bit off the beaten path, going off grid, and just using that as a way to learn a bit more.

One thing led to another, and after finding out that I could remove one of the bellhousing side from the transformer, and that that it by some freak coincidence just perfectly fit in the transformer cut out of the JTM45 chassis.

OK, but at this stage, I still didn't know if the transformer was still good. I mean, I thought it was, but you never know. So I bolted transformer in, did a rudimentary connection to the mains, and then measured the HT windings and some others. Success! Not dead! And thus, a project was born!

I'd been toying with the idea of making a clone of the Fortin Meshuggah amp (yet another modded Marshall(tm) if you look at the schematic) so I kind of decided that I'd go down that path, and just use things I had, like the power transformer, and the chassis which fit together so nicely.

So, that was phase 1. I was going to build a clone of it. Awesome.

And I was going to do my own turret board as, well, why not...

But then, then things started happening...

I had this thought, which kind of came from really liking the forin 33 boost clone I'd built last year. I had a spare board. I could, you know, add that in. And I could make it switchable, via a front panel toggle. That would be cool I figured. 

Then I started thinking, i mean, what if I made it footswitchable? Wouldn't that be cool? 

This kind of opened the gates to feature creep somewhat. If you've ever worked in software, you'll know "feature creep" is where you get asked to build the program equivalent of a shoe. And then little things keep getting added, and before you know it, you're now making a shoe with jet engines, wheels, little wings, a satellite dish, miniature kettle and an anchor instead of brakes. So yeah, more things got added to the list.

So, boost board, cool, we can do that. But maybe I'd like to footswitch the 2 "channels" instead of swapping the input jacks to get the effect. OK, I reckon I can do that. Looks like it'll be a doubnle relay as channel 2 has a capacitor to ground. OK, I can do that...

So now we're up to 3 relays.

Then, then the next idea happened about 47 seconds after watching a lee jackson marshall mod video.

My brain tickled, and I asked "the" question. What if I wanted even more gain (because the meshuggah amp definitely does not have way more than enough gain already. And the boost won't have added any gain either at all... *cough cough*). That'd be a great idea. I can also make that switchable.

So there it happened. 4 relays.

And to make sure I didn't chicken out, 15 minutes later I'd drilled out a new tube socket hole in the chassis (first time for everything, it's a little off, but I can live with it, like 1-2mm closer to one tube than the other)

 No matter though, it's all about the intent. 

And to make the intent more intentfull, i went of and wired all the heaters to the sockets. And thus, mistake 1. I forgot the power tube sockets are bolted in 45 degrees off to what I am used to. Cue me wiring the heaters to pins 1+6 instead of 2+7. Stupid. Easy fix having spotted it now, but still stupid. Stupid as in if I hadn't of seen it now, it may well have caused some kind of fun tube or amp death and maybe magic smoke at some point. However, I'll never know as I caught it before it was too late. Phew!
 

 

 

Next bit, seeing as I was there, was fitting the cap cans. Here it turned out that the chassis was drilled thinking you'd be using a small little 45 or 50w power transformer, not a retarded big 100W one. Plus, the clamps I had, wouldn't fit, so I needed to redrill new holes. Eventually after enough procrastination, drilled them, just about fit, and m,ounted the cap cans. unfortunately, the clamps aren't dead centre around the hole, so the terminals on the cap cans look a little close to the chassis. I'll revisit when i wire them, and then maybe heatshrink, electrical tape, or most likely as it's the most fun, a hot glue gun, because, hot glue guns are awesome!

So there we have it. I've got ferrite beads on order, magical mustard caps, some sick as hell R


ussian radiation pilot lights, a 50w slo output transformer, 5H choke, and many other bits (actually, this is a lie, I have them already, but i wanted to build up suspense for next post)

I'm going to taking my time with this one, seeing as I'm doing a few things for the first time here, and this one might take a bit longer, but that's ok, as I'll hopefully learn a ton as I go along.

 

Defeat snatched from the jaws of victory... And rescuing it back (a tale of idiocy and woe)

So I totally forgot to write anything for a while. Not because i'd stopped doing anything, but more because good intentions, and then just forgetting to, and, well, a slight mishap...

Anyway I finished the build beginning of June? Or something like that. Bit more wires than the sloclone, but got there in the end, even drew some skull on cross bones ontop of some caps to remind myself not to be stupid and lick them.

It all mostly went well, apart from that just like on the slo, the OT anode wires were the wrong way round again, and I found a mistake on the layout vs the schematic that meant i had no signal to the power amp. Important lesson here, trust the schematic, double check against the layout.

I'd done pretty well with neat wiring up to that point, but then had to concede and do a bit of rewiring and de soldering, but eventually, it all worked. Big thanks to the oracle for not getting sick of me, as I asked a lot of questions in the depths of despair...

So yeah, it came out really cool. I had some preconceptions about it maybe being too nice, but i think having the option of 20v zeners as well as stock Friedman values nicely added a bit of aggression to the amp, and it was brilliant! All was well with the world, apart from total inability to do woodwork (you should see the ghetto chicken door i made, and even did it without losing fingers, but it's definitely not an oil painting...)

But then, yeah, I killed it. Wondering why it stopped working, i was poking around in the amp, and here, dear reader, follows a tale of caution, entitled "don't be this stupid, and put dowen the screwdriver"

So, i decided, in infinite wisdom, to go tapping power tube pins with the screwdriver. The input jack I figured was iffy as it had been loose, but after tightening, and poking the wires, it was still not responding. Patient was braindead, but still had a pulse (ie, pilot light came on, transformers humming, valve heaters working).

All good. But does it make sound from the power amp? How shall I test this? I know, lets tap a pin with the screwdriver to make it go "pop", that way I'll be able to know it's the preamp.

What happened next was a moment of idiocy. The idiocy being that I thought this was a good idea. There was no voice of common sense sitting on my shoulder screamning "noooooo" (he'd gone on holiday to a day spa or something) so I did it. In went the screwdriver, and then, slip went the hand....

Now, we all like firreworks, they are cool, we like bangs too. Just not in an amp you've just built. The screwdriver (i think) shorted the pins between high tension supply and heaters. One big blue flas, and small bang, and now, nothing. All dead. No pilot light. No hum of transformers.

Dead.

Really Dead.

Really really dead.

Having taken stock, and after a fairly long period of silence staring at the amp, I checked the fuse. OK, so that's gone, maybe that's it.

I replaced the fuse. Still nothing. Measured voltages, nothing coming in at all. 

I looked, and looked, stared, consulted the (by now probably fed up) Oracle, but all to no avail. My diagnosis? Fried Power Transformer.

And thus, I left it. It had lived, briefly, and then died. Life happened. I did things, worked, summer went, the days grew shorter and it lay there forgotten. To repair it, I needed a new Power Transformer, and there was other stuff to do.

Then when i tried to order, the guy who makes them was unavailable. So again, the wait. 

Finally, beginning this year, i put a large order in. Not only was I going to fix it, but i was going to finish the second BE100 build I'd started, one that was using the Russian PCB I'd got (don't worry, I'll do a quick post on this one, as it's much the same as the BE100 build, unless, of course, it goes hilariously wrong, in which case the story might be longer).

So, got the transformers, and then one evening, not too long ago now, set about replacing the fried power transformer.

I even got some xt60 connectors so i could just plug it in, instead of desoldering from the board. These are cool by the way, used in RC cars, and can handle stupid amounts of current.  

So, I then, having rewired it, turned the amp on. Nothing. Nothing again. At this point my heart sank. Have i screwed it that badly that it's silently taken out the new PT? So I checked the fuse. All fine. Really, what is happening here?

 

Then, the penny, it dropped. The penny that read "Hey Stupid" on it. I checked the fuse holder. Now, it has two places the fuse can go. One is difficult to put it in, one is not. So i took the fuse from the difficult place, and put it in the easy to put place. 

 

Then, turned it back on. It works! Lights on, yes!!!! Still no sound, but, closer!   

So, time to have a look, and there it was, the culprit. A strand of shielded wire grounding the input to the chassis. That's what the problem was that caused all this mess.

So, as a result, I am now (after watching a lee jackson amp mod video) putting heat shrink on all the ends of shielded cables now, to avoid that happening. A rather long winded lesson I must say...

So, you may ask, does that mean the other Power tranny was fried? Well, not to spoil too much, but the answer to that question may very well involve subject matter for some future (not too far in the future) blog posts!

Meanwhile, here's some pics of incorrect, followed by correct places to put a fuse in an integrated mains IEC plug. Enjoy, and remember, I've been dumb so you don't have to be...

Anyway, until next time, when I'll be introducing a new project, and explaining how I will be torturing myself with this one.