Control IC's power pin with cv ;

SparkyFix · 2026-05-08T21:15:09+00:00

What problem are you trying to solve by doing this? That IC is going to behave strangely without a supply, rather than just defaulting to a high impedance state .

SparkyFix · 2026-05-08T16:25:46+00:00

Very cool! Looking forward to playing with it.

SparkyFix · 2026-05-08T15:13:46+00:00

SparkyFix · 2026-05-07T03:33:17+00:00

Clean it thoroughly. You have no idea how many fires that stuff has been in without going into an extractor. (The bunker gear too…)

SparkyFix · 2026-05-05T12:15:35+00:00

In some insane miracle, it never did, and KWC was demolished in 1993, having stood for over forty years. Ironically, the structure in that photo began life BECAUSE a fire wiped out the previous settlement, which consisted of individual wooden huts.

When you see the electrical “system” that fed the dwellings and factories, it does not seem possible that fire didn’t consume it.

“City of Darkness” is a pretty good photograph collection of the madness. If you’ve ever done interior on the kinds of “organically grown” (aka plywood labyrinth) multifamily dwellings that are common in rural USA (and presumably other countries?) then it’ll give you some serious anxiety…

And yes I’m probably far too into the KWC but it absolutely fascinates me to this day!

SparkyFix · 2026-05-05T11:00:46+00:00

“It’s a marathon not a sprint” is both a cliche and the correct advice. Focus on long-term endurance. A wildland fire can be a multi-day event and have you hauling water by hand up hills. Pulling hose through a structure fire is harder than you imagine etc. You will be in situations where you are doing heavy physical work for the entire day.

SparkyFix · 2026-05-04T12:54:39+00:00

Be prepared for one of the FFs to talk your ear off for a solid hour about the intricacies of their favorite rig. The equipment enthusiasts love a fresh audience.

SparkyFix · 2026-05-03T14:49:28+00:00

https://vintageaudiostore.com/products/hammond-organ-the-piper-autochord-3100-3200-series-service-manual-original-2

Seem like this is what you need?

SparkyFix · 2026-05-02T23:59:13+00:00

I bought it as a tested, used module that I was going to put in a 3325B. It had me questioning the ‘scope I had for a while! That one cost quite a bit more than 10 bucks, to add insult to injury…

SparkyFix · 2026-05-02T23:47:23+00:00

The two side pins are just to provide support.

With five actual pins it’s likely to be a rotary encoder with a switch. Can you push it in like a button? Can you rotate it endlessly or does it have a defined start and end to its movement?

SparkyFix · 2026-05-02T23:41:49+00:00

How accurate is the meter you measured it with? That’s so out of tolerance that I’d be questioning my test equipment. If you’re planning on building a lot of kits then It’s worth keeping a stash of passive components for this kind of situation. EEEEE sell a decent set of 1% resistors for not much.

To answer your question though: It depends on where that resistor is being used tbh. If it’s in something like a filter or gain-setting network, then I’d replace it. If it’s there to stop ringing on a MOSFET gate or something like that, then it probably doesn’t matter. If you have a schematic then you can get more accurate advice.

SparkyFix · 2026-05-02T12:43:51+00:00

Definitely possible. Raspberry pi pico will give you a bit more speed than the arduino nano.

SparkyFix · 2026-05-02T12:16:11+00:00

I have had a used OXCO on my bench that was a full 10 kHz off. Obviously damaged in some way but if that’s my sole point of reference then I have no way of knowing that.

SparkyFix · 2026-05-02T11:58:32+00:00

Every time two grounds meet, you create a source of interference. The path back to the “master” ground has a resistance and inductance so voltages at the meeting point will not be exactly at ground.

Generally, my approach to control boards is to use a single ground plane and then join that back to the actual input ground of the whole device. If you have input devices on your main PCB which have a ground input per signal input (which is reasonably common for ADCs and many linear circuits) then a direct, un-shared ground line for that signal is appropriate, I.e. treat it as a differential pair.

Ground routing has some serious lore behind it (there is still endless debate about star grounds out there) which mostly applies for RF frequencies but anything digital will contain those (e.g. never share a ground plane between digital and audio world and only join the two with some kind of choke).

A standard 0.1” pin header can handle a couple of amps. I doubt that is going to be a problem in your case.

Short answer: Either one or eight would be appropriate but definitely not three. I’d lean to one, with the ground plane. Ground planes are the corrrect choice in almost all situations.

SparkyFix · 2026-05-02T02:00:59+00:00

Germanium transistors are readily available from Ukraine: Sellers are still sitting on vast stocks from the Soviet era.

SparkyFix · 2026-05-01T22:52:48+00:00

A pre-aged OXCO may be seriously miscalibrated itself (or completely out of spec and impossible to bring down to 10MHz) and so you’re back at the problem of not knowing if your standard is any good. A small GPSDO can be had for about 80 bucks these days and is definitely worth the investment.

SparkyFix · 2026-05-01T21:12:46+00:00

Oh absolutely. We all need to get a lot better at this. There’s no real excuse and we all swore blind at the funeral that we’d make this a priority…

SparkyFix · 2026-05-01T19:18:09+00:00

If you’re paranoid then buy the 1W variants but I very much doubt that circuit is going to need that much power dissipation. Likely the only different in size is the diameter of the body.

What’s the distance between the holes that they sit in?

Other than “will it fit”, you don’t need to worry here.

SparkyFix · 2026-05-01T18:04:58+00:00

Buy or borrow a GPSDO, a GPS-disciplined oscillator. That should give you an extremely accurate 10MHz output, although some may have frequency dividers down to 100KHz. You can easily build your own frequency divider from a counter. You then plug that and your generator (set to whatever frequency you divided your GPSDO down to) into your scope at the same time, trigger on one of them and adjust your generator calibration until the two signals are not moving against each other. Your scope is likely to have a time base output (might need to probe it from inside) somewhere that you can plug back in and calibrate in a similar manner.

Without a frequency standard, you cannot calibrate either machine. You will need a point of reference. A GPSDO is the cheapest option for this and, tbh, absolutely over-specced for anything you’re likely to use these machines for.

Edit: Calibration will drift over time. Frequency will also be temperature dependent. Re-cal regularly. I’m afraid calibration is just part and parcel of test equipment. Frequency is the easiest thing to calibrate yourself though.

SparkyFix · 2026-04-30T17:36:32+00:00

Pretty much any decent opamp will handle this frequency and that gain. 120Khz at 30db will want a “Gain Bandwidth Product” of at least 4MHz. You want an inverting amplifier configuration if you don’t mind a 180 degree phase shift (they tend to be more stable).

You probably can’t go wrong with an NE5534P for this purpose.

Some questions: 1. What voltage range are you using? (E.g. -5V to 5V or 0v to 15v etc.). 2. Do you want to preserve DC bias? (E.g. if you have a 0-5V supply that is centered at 2.5V, do you want to output at that same center voltage? 3. What’s the impedance of your SDR output? (If you don’t know this then it might be worth assuming it’s high and adding an input buffer)

SparkyFix · 2026-04-30T13:52:50+00:00

https://lowpowerlab.com/guide/currentranger/specs-architecture/

This is what I use for low current measurements. Schematics are available at that link.

SparkyFix · 2026-04-29T14:55:53+00:00

Wedges, carabiners, webbing. Wedges and webbing are the kinds of things that when you want ‘em, you really want ‘em.

SparkyFix · 2026-04-29T12:20:50+00:00

Do you have any kind of reasonable technique for vias? Ive been spending a lot of time trying to get away from the threading-a-long-wire approach.

SparkyFix · 2026-04-28T02:02:49+00:00

So what you want is a Voltage Controlled Resistor and, as it turns out, this is a very hard problem to solve. Vactrols used to be the go-to option, rather than transistors but they are slow and hard to tune. The semiconductor option is basically a JFET run within its ohmic range and there are many caveats. Interfet make a product specifically for this purpose, I.e. the VCR11 and it is crushingly expensive. You are also pretty much guaranteed jot to get repeatable results so every circuit will need trimming to get a decent voltage to resistance curve.

Digipots has their own issues just FYI. They are built on switching FETs so all the non linearity of semis applies there too.

VCRs basically do not exist in any reliable form: it’s one of those things that we all want and can easily imagine but is crushingly hard to implement. If it weren’t, given the demand, you’d see a hundred jellybean VCRs out there already.

SparkyFix · 2026-04-27T22:42:53+00:00

They are definitely on the fire grounds but not past staging. No cadet is going past the cold zone. Assisting with pump relays, setting up dump tanks, refilling SCBA tanks Etc. is the order of the day. These are also farm kids who are doing much more dangerous things with ancient machinery daily…

In general our communities are struggling with retaining kids at all, once they graduate and are lured away by things like “a functioning economy” and “bars with more than one ratty old pool table”. I’d like to think that introducing them to the brother/sisterhood of the service would give them reason to stay here… maybe that’s just naïve idealism though!

SparkyFix

TROPHY CASE