I make a point of getting out in nature for a stroll at least a few times a week, but this &^%$ pandemic and my chemo vacation have given me the time & mental energy to finally get serious about the Beamer layout.
I’ve “finished” a chassis drilling drawing (maybe 2 more holes…) to give to my son & his milling machine, and I’ve been making progress on the electrical layout and one part is done. Knowing that maximizing the IN-13 performance would require some experimentation, I wanted to lay out the circuit on a small prototyping board (and use trim pots in a couple of extra places). This Adafruit board is only 2 x 1.7 inches and looks like it will do the trick nicely:
Note that the B+IN13 supply rail goes directly to the tube. Did you spot the change from the schematic?
The full chassis layout looks a little different, but uses similar shorthand. Components are just sketched in with rough sizes & only enough detail to identify the part; parts overlap without any indication of final 3-dimensional status. The emphasis is on connections while ensuring enough space.
First: I give up — The Beamer is gonna be the name.
Second: In addition to the Nasty/Nice channel switch & LED, the new schematics include circuitry for this IN-13 linear indicator tube I’ve always wanted to use:
The active length (between the two red lines) is 4 inches, so it should look great if I can come up with a good way to mount it (horizontally). The schematic currently has it getting the signal after the Master volume, but I’m thinking it’ll probably end up tapping the signal just before that pot, so it’s not boring at low volumes.
The spec for the IN-13 has me thinking a standby switch is probabaly the simplest way to (mostly) adhere to the startup recommendations, so that’s back in.
I haven’t done any detailed layout yet, but I have decided that – for both electrical layout and control clarity reasons – it will be best to place the input jack between the Nasty & Nice volume controls. I’m also planning on using different/larger knobs for the Nasty, Nice and Master volumes:
Drive Tone NASTY jack NICE Bass Treble MASTER lamp
The red LED will go above the Nasty knob, and the channel switch will go above the input jack.
Tuesday (6/17/2020) I spent the afternoon by the bay, recording this wind sculpture by Dave Ayer. He was hoping for high wind speeds and I wanted to test my fuzzy blimp windscreen on my shotgun mic.
There was wind, probably even up to 15 mph, but most of the time it was probably only 5 mph or so. It meant some long stretches of soundless sculpture, but sometimes I’d also catch several minutes of reasonably frequent and varied excitation.
Here are a few excerpts:
The shotgun picked up the sounds of the sculpture well enough, but was disappointingly non-directional. Those crackling noises are very dry leaves blowing along the path.
While avoiding the layout of the next version of the prototype, it ocurred to me that I haven’t even shared that schematic yet.
So I’ve started a Beamer page [<– over there] with PDFs of the three pages of the current schematic. This is essentially the current prototype as it will be built into a fresh box, with something close to a final layout. Be aure to read the notes…
Then I’ll play with a few Rs and Cs to perfect the sound!
Re-entering amp design mode has meant having to generate schematics, which has never been something I could do well in freehand. When I was still at Logitech, I could use my OrCAD license for tube projects as long as I could provide the vacuum tube (valve) library, but those days are gone and I’ve had to look for an alternative.
A little searching led me to KiCad — a totally free EDA tool suite (from folks at CERN!) that even has library parts for a few common tubes/valves. It’s easy to use, and has library parts for most anything you’d need in a tube amp. The weakest library (for tube stuff) is the transformers, but there are reasonable ways to get around that (see my next Beamer schematic).
Now I’m trying to make myself plan a proper layout, but since I don’t use PCBs that’ll be in a 2D mechanical CAD program. I’ve just started to get serious about it, but LibreCAD looks promising…
I’m not crazy about “Beamer” as an amp name (derived from the push-pull 6BM8 design), but that’s all I’ve got. Suggestions are welcome!
The more I look through my schematics & notes from 15 years ago, the more I realize that my Beamer project really wants to be a stripped-down Verberator II: no reverb or tremolo (we have boxes & software for that these days), just a wide tonal range, from clean to dirty.
Today I dug out my old Verberator II prototype (grrrr: link not working) chassis and immediately realized that I’d already done much of the work toward a Beamer. I suspect I gave up on it (and amp building) because the tremolo was more than I could master. With all the crazy shit you can do with software these days, it makes sense to leave that to post-production and concentrate on the core function (TONE) with electric guitars. So we’re talking about a gain pot, a foot-switchable ‘boost’ stage, and a master volume, with one or two tone stacks (or single-pot controls).
Fifteen years ago(!) I built the Highway 86, my last tube amp project that made it all the way to finished. I put in a little time on prototyping Verberator II / Murgatroid ideas after that, and ended up bailing when the amp ideas and life both got too complicated.
The point is, the Highway 86 is good enough that a friend offered me $700 for it! I couldn’t let it go, but it sold me on simple amp designs. We’ve got plenty of great hardware & software available for reverbs & effects, but the sound & response of real tubes are what keep me playing guitars.
I may someday get back to the Verberator II or the Murgatroid concepts (or combine them), but recent garage cleaning uncovered a trove of old tube amps I had acquired for parts on eBay over 10 years ago, which required me to think about which parts are worth keeping.
Two of the old amps are stand-alone hi-fi stereo jobs from the 60s with push-pull 6BM8 output stages, which means I have 4 output transformers that should be pretty similar. So naturally I’ve got this crazy idea of building a short run of 4 amps with the same design. I’m thinking maybe a preamp like the Decimator and a power amp along the lines of the Highway 86.
But first … I have to clean up my man cave enough to make space for tube stuff again!