Electronics

This… is stupid

(IMO, of course. And Geek Alert)

MFJ-949E

This is the switch and tuner schematic for an MFJ-949E Versa Tuner II. Great little unit, with a built-in dummy load. It has a switch that selects the dummy load, then the three antenna connectors in pass-through mode, then the three antenna connectors through the matching network, and then the dummy load again… through the matching network.

Which means that if you want to tune into the dummy load, you have to use the setting all the way to the left, or you have to adjust the tuner to match the dummy load to the rig, using the switch setting on the right.

Now why would you need to match a 50 ohm dummy load to your rig? Insane. The dummy load switch setting on the right should connect straight to the dummy load, not via the tuner.

I have a soldering iron, I can fix it.

2017-07-15 by wrm Electronics Geek ZS1KE 0

New life for your FT-290R

I mentioned previously that I figured out how to make a new display for an FT-x90R. My own rig is still in pieces ‘cos I’m not quite happy with the software yet (or actually, with my reverse engineering of the display protocol, but it’s the same thing in the end).

But Dave ZS5DF wanted his rig fixed so I fitted a new display, even though it doesn’t have the ~~F key~~ “P” priority display function in firmware yet.

P1130871r

Two filament bulbs, because the replacement display needs light from the right-hand side and the S meter is on the left-hand side.

P1130882r

Component cost is close to R500 which almost puts it in good-money-after-bad territory but I like these little radios.

2016-12-12 by wrm Electronics Geek ZS1KE 0

School project

Younger kid had to build an electric motor for a school project. Having a garage full of stuff, it was no hassle to find everything required to build one.

motor

I made her wind the coil.

But the question is, how do kids complete (or even conceptualise) something like this if they don’t have a Wouter around the house?

goes

2016-10-12 by wrm Electronics Geek 0

From the Junkbox

C1166

This is a C1166 Pulse Tetrode made by English Electric, who also made transistors. Good for switching 17 500 volts at 15 amps. But only for 1 microsecond every 1 millisecond (1T4 and AA battery for scale).

The filament alone needs almost 60 watts (9 amps at 6.3 volts).

Quite useless unless one wants to build a glowbug radar or something. But quite marvelous in a way.

2016-08-31 by wrm Electronics Farting around Geek 0

Look what I got

Mahala gratis verniet and for free, nogal.

And it seems to work, that’s indeed a 4.7k resistor.

Look at the ridiculous scale on this thing — not only uA but nA as well. Why would I want to measure a nano-amp?

I think this will become part of my permanent test setup.

2016-02-16 by wrm Electronics Geek Get Off My Lawn 1

Fun with a Power Supply

Oooh look! Someone threw out this perfectly good Spectrum SPL-603 power supply!

Well, mostly perfectly good…

She who was once the beautiful 723

The 723 had given up all its magic smoke, to the point where the socket is also buggered. Fortunately this is a stock part in my junkbox, as are 2N3055s (the one output transistor was shorted emittor-to-collector, but I can’t explain why this would break the 723). I also replaced the H1061 with a BDW93B because I could.

Truth be told, this is a terrible PSU.

The non-regulated DC is 52V, which means that at 30V output the transistors are dropping 22V and at 2.5V out they are dropping just about 50V. No wonder two 2N3055s are needed for a measly 3A output (A 2N3055 is good for 15A and 115W, so when dropping 50V you can only get a smidge more than 2A out of it, and that with a good heatsink).
The 723 Vcc is connected to the non-regulated DC, but the 723 is rated for 40V max Vcc. This is probably what broke it.
When I set the PSU to about 6V and turn it off, there’s a ~20V spike on the output. WTF?

So why the high non-regulated DC? I thought maybe it drops under load because cheap transformer, but this is not the case. The transformer gives out 38VAC which drops to 35VAC with a 1A load.

The general schematic is similar to http://www.circuit-projects.com/cimg/2V_to_7V_8A_power_supply_by_723_and_7812.gif but with a difference — the base of the current limiting transistor is connected to a voltage divider (R4/R5) to ground. This causes the current limiting point to be higher for a higher output voltage. Again, counter-intuitive.

So I changed things around to how it should be. Fitted a different transformer, from an old UPS — it’s only good for about 18V out but that’s enough for me. Not going to try to make a purse out of this sow’s ear.

2015-09-04 by wrm Electronics 0

Brewday!

My new brewing setup. A nice large stainless steel urn with a dual element, and a cooler box with a filter that used to be a braided hose and a tap.

The box under the urn is a PID controller so that I can (in theory*) dial the temperature, have a homebrew, and have water at the right temperature on tap.

It’s not going to win a panel wiring contest, but it works. The PID doesn’t have the switching capacity, so there’s a solid state relay. I also wired diodes to send the positive part of the AC to the one element and the negative part of the AC to the other element to spread the heat.

The switch controlling whether the diodes are in-circuit or not comes from the junkbox. Been a while since one could buy something useful for R3.45.

Grain in the cooler (this is 6 kilos of pilsner, on Saturday), add the water, let it be for about an hour…

..and drain the good stuff (this is Sunday’s brew, an IPA).

The pilsner is all-grain, which means that you end up with quite a lot of liquid to boil.

That’s the next step. The urn, on low, should be able to boil the wort as well. If not, I need to get a 30 liter+ pot, I have quite a few gas burners.

Good news is that both brews started bubbling easily (I added Servomyces to both and DAP to the IPA). The pilsner is my first all-grain and my first lager — I’m using ice to keep it cool.

* The water coming out the tap seems about 5C too cold. Some calibration required, looks like.

2015-08-24 by wrm Beeeeeeer Electronics 0

No. No, I wasn’t born yesterday.

Thank you for asking.

Background: I think I found a way to fix a broken display on my Yeasu FT-290R 2m all-mode radio. A broken display on these things is common, and displays are very much NLA. The FT-290 (2m), FT-690 (6m) and FT-790 (70cm) are all pretty much identical except for the RF bits, so a fix for one is a fix for all.

So I advertised on swop shop, looking for an “FT-290R / FT-690R / FT-790R”.

Hello Wouter ,

Thanks for the mail. I have the requested FT-290R / FT-690R / FT-790R
in an excellent condition I will be shipping via FedEx courier on a 3
working days delivery and will accept payment via Western Union or
Money Gram.

Location: USA

What’s your complete shipping address?

First and foremost before proceeding with transaction we can only
accept payment via western union if you are satisfied with that kindly
get back to me.

Maybe I should ask for a photograph of this “FT-290R / FT-690R / FT-790R”.

2015-07-15 by wrm Electronics Farting around Geek ZS1KE 1

Ross Micro Eight (RE-815)

Some people collect tiny transistor radios. I don’t have enough of them to call it a collection but I guess I’m working on it.

The Ross Electronics Corporation imported transistor radios from Japan from 1955 to about 1970. They were located at 589 East Illinois Street and later (I think) 2834 South Lock Street, Chicago. As far as I can tell, there’s no relation to the Ross Radio Company of Youngstown, Ohio.

Here’s a better image of the schematic on the inside of the back cover (yes, there was a time when radios came with schematics).

It would be a mistake to expect good performance from a 1965-ish design running on one 1.5V cell, but the performance of my one is beyond mediocre. But then again, I didn’t really buy it to use it.

Mike has a nicer one, in a box nogal.

Obituary for Eli Ross, July 8, 2006.

2015-03-16 by wrm Electronics Farting around Geek 0

Old friends, now obsolete

Ah yes, New Years’ resolutions. Gotta love ’em.

However, I have too much stuff. There. I said it. I mean, I firmly believe in the William Morris quote, however, times have changed.

This collection of Elektor magazines I grew up with — obsolete.
A collection of GE Ham News that someone spent money on to have nicely bound — obsolete.

Byte magazines? Obsolete.

Creative Computing? Not quite yet obsolete.

And even if I can’t find it online, scanning and dumping* is better than storing the originals until my container is auctioned off one day.

Don’t get me wrong — I’m still keeping mountains of stuff. Just not… this stuff.

* Yes, Jason doesn’t like dumping. I’m not dumping anything that’s even slightly rare, so chill.

2015-01-14 by wrm Computers Electronics Geek Get Off My Lawn 0