Back in Business

Last week I finally had the energy to debug the Beamer. It turned out there was a cap on the the Treble control that was only conected at one end. Doh!

So now I’m making noise again, and ready for some tuning. The first order of business is to try a little negative feedback from the output transformer. As the master volume goes up the low end gets a litttle too rough for what I want from the Nice channel. I might also need to reduce the output from the preamp as I suspect it gets too hot for the phase splitter at high Preamp volumes.

Next I plan to experiment with R19 on the preamp schematic, which sets the knee frequencies for the Treble and Bass controls.

THEN I’ll start playing with the Nasty channel, with the goal of getting usable tone over the full range of the Drive and Tone controls.

Back to work…

What a year

Sheesh! Three weeks after that last post I started on a new chemo regimen and it’s been all downhill ever since. Not just the expected fatigue and G.I. issues, but getting cumulatively worse every 3-week cycle.

The nadir was just over 6 weeks ago, when an attack of vertigo coincided with a chemo infusion. Couldn’t keep *anything* down for two days. The vertigo is pretty manageable now that I’m used to it, so Thursday I went back for another infusion (at 75% strength).

The Beamer is pretty much re-assembled (minus indicator tube), but I have some debugging to do. My test signal isn’t even getting out of the first triode. I should be able to figure it out if I can just manage a couple of hours of concentration…


Deconstructing Beamer

I’ve obviously been taking my time with this project, but I never intended to build half of it twice!

I was getting occasional, unexplained changes in B+ voltage readings since the first power-up, but the preamp behaved pretty consistently, so I let it slide. When I started looking at the power amp it was obvious that the signal wasn’t balanced, and I eventually determined that something fried one of my 6BM8 pentodes. After a few fried tubes and much inspection & general poking around, I realized that there must be an intermittent connection to the tube and that the connection was in one of the sockets.

Back in the day, when I was buying tubes & parts that might be useful some day, I found a guy in Lithuania on eBay who had acquired lots of Soviet parts and equipment when it fell off trucks as the Russians left for home (or something like that). I got lots of good deals on parts & tubes from him, but these ceramic sockets are a bust. They might work OK most of the time, but can’t be re-tensioned when the fit gets loose. So, after just a little wiggling (like inserting & removing a tube a few times) the socket holes can — and do! — get loose & intermittent.

You can see here that once the contacts on the left get loose, you have no way to get somethng in there to re-tension (smallify?) them.

So now I’ve replaced all the ceramic sockets & re-wired the heaters, but I need at least a sketch for a new layout of the rest before I finish rebuilding. Fortunately, the replacement sockets fit in the existing chassis holes, but the the orientation of the pins is rotated 90 degress relative to the screw holes so all the point-to-point work around the sockets has to be re-done from scratch.


Health/Life update

I just realized it’s been a year since I’ve said anything about my health status.

I started chemo in January and had a bad reaction to it (interstitial pneumonia) in May, putting me in the ER on June 1 with my O2 level at 60%(!). Got tested for covid first, of course, and then a hefty dose of steroids and spent most of the day with a CPAP mask on. By evening I was off the machine and getting my supplemental O2 through one of those nasal rigs. They kept me there for 2 nights and sent me home with an O2 tank, using the lowest possible flow setting because the steroids really did the trick.

At home I used an O2 “concentrator” with a 50 foot hose for about 6 weeks but barely needed it after the first 2. I also had to do a long taper from the steroids (2 months), which made for some manic high-energy weeks. Most of that energy went into music-related projects, often at 5am (and mostly still unfinished).

The best part was that all this meant I was off chemo at least until I was fully recovered. Then my August CT scan showed that my nodules had actually shrunk a little bit so we decided to wait & see before ending the chemo vacation.

I got another 6 weeks to enjoy without chemo, but unfortunately that coincided with the heat & smoke waves of this California summer/fall. The Beamer has been slowly progressing in all that inside time (update coming soon).

But my latest CT shows the nodules growing again, so I’ll be going back on chemo right after Thanksgiving. This time I get to choose between 2 new chemo regimens and a clinical trial. I’m gonna stick with a chemo for now, but the number of options is encouraging. If the chemo I choose doesn’t work (i.e., continued growth) I can try something else.

I’m prepared to play Whack-a-mole (as a friend calls it) for as long as I still have options. That could be several years, yet…

Almost time to start soldering

Here’s the layout plan (for everything except from the OT secondary to the outputs, which are trivial to do):

Beamer Layout

It’s easier to read when printed, but the different sections of wiring are on different layers, so on-screen I can choose layer colors that emphasize the section I’m working on. I’ll post the LibreCAD file when I have time to work around WordPress (it won’t upload .DXF files).

Finally getting serious about layout

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:

This is the layout I generated in LibreCAD for the IN-13 circuit at the left side of the power amp schematic page:

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.

I’m getting pretty good at LibreCAD, btw…

Beamer X21

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. shows 10 of them used on a spectrum analyzer.

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.

Schematics on the Beamer page…

Wind Sculpture Field Recording

Recording the sculpture

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:

Dave Ayer’s Wind Sculpture
June 17, 2020
Seaport Blvd.

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.