New battery for the Voltohmyst

Finally got around to replacing the old corroded soldered-in D cell in the RCA Voltohmyst with a new battery today.

1.5V Battery
1.5V Battery

Snipped the wires off the battery and into the trash it went. Had to drill out a rivet to remove the battery holder clip.

Voltohmyst battery removed
Voltohmyst battery removed

The battery holder is a little on the big side and just fits into the space vacated by the old battery and clip. Soldered the wires onto the battery holder and fastened it to the Voltohmyst using some double sided tape.

New battery holder
New battery holder

Now it’s got a new battery that can be replaced whenever it’s needed.

New battery installed
New battery installed

Next thing to do is go through the  manual and read up on how to calibrate the meter.

Museum Ships Weekend 2018

I ended up being busier than originally anticipated and was only able to operate in Museum Ships Weekend for a few hours Saturday afternoon.

I started off with doing some logging. Band conditions on 20m were pretty crummy and there wasn’t a whole lot of activity we could hear, but we managed to hunt down about 6 other museum ships.

Then it was my turn on the radio and managed to nab a couple more museum ships. Found an open frequency to start calling on, made a few contacts into the Midwest and Northeast. Then a pileup happened and I was working stations as far as CA, and even a few DX stations (Austria, Belgium, and Italy). That lasted about 30 minutes, and then as quickly as the band opened, it shut down again. Towards the end, static crashes from thunderstorms rolling in from the west obliterated any signals we could make out on 20m.

I decided to call it a day around 6PM and turned things over to the evening crew, but I’m not sure they were able to dig up much more activity even after the thunderstorms went by.

There were about 48 contacts, including 10 museum ships (I think) by the time I left. I’ll find out later how the rest of the weekend went.

A new oscilloscope

Saw someone at the TARC swap meet with one of these little Tektronix 222 DSOs for sale, so I bought it. Terrific timing since my Hitachi oscilloscope died a while back and I still haven’t gotten around to looking into it.

Tektronix 222 oscilloscope
Tektronix 222 oscilloscope

It’s little, and doesn’t have a lot of capabilities but I think it will do pretty much everything I need (at the moment). It comes with two scope probes that are permanently attached. It’s designed to be powered with an 8V SLA battery, but it looks like batteries with the right form factor and voltage aren’t readily available anymore. I did find a promising looking battery replacement project though. This one didn’t come with a battery, but a standard sized power jack lets you power it with wall power. It’s even got a RS-232 serial port!

The scope seems simple enough to figure out how to use without a manual, and I was even able to find a service manual online to download.

Here I’ve got one of the channels measuring the output from one of my Etherkit Si5351 breakout boards. I don’t remember what I have my RedBoard making the Si5351 do, but I seem to be getting a pretty good signal out of it.

Tektronix 222 display
Tektronix 222 display

A new power supply

One of my acquisitions from today’s TARC swap meet was a variable power supply. The person I bought it from acquired a bunch of these from a school district surplus auction. I’ve been wanting to get a variable power supply for the workbench, so I bought one of them for $20. Seemed like a pretty good deal. Almost grabbed a second one from him.

Variable power supply
Variable power supply

Banana jacks provide AC and DC outputs, and voltage for both is controlled by the knob on the left. Two meters show DC volts and amps, but if you’re using the AC output, you’ll need to measure it yourself.

The panel indicates the power supply will do 0-20 VDC and 0-25 VAC. With no load, the power supply topped out at 35 VDC and 26 VAC. This is an unregulated power supply, so any load is going to bring the voltage down.

Max 35VDC unloaded
Max 35VDC unloaded
Max 26VAC unloaded
Max 26VAC unloaded

Getting inside the power supply requires removing a total of 18 screws (6 on each side, 6 on the top). Seems a bit excessive to me, but I didn’t design the thing. Once the screws are out, removing the top exposes the innards.

Power supply innards
Power supply innards

Not much to it inside. There’s a big beefy transformer which accounts for almost all of the power supply’s weight. Voltage control is performed by the variac. A large (and loud) 120mm fan (lower right) provides cooling.

The key just turns a metal plate that flips the actual power switch on or off.

Power switch
Power switch

The cooling fan gets its own power supply so that it’s not affected by changing the output voltage.  It’s just a 12V wall wart that gets powered from the AC input I think (haven’t traced any of the wires to see what goes where).

Cooling fan power supply
Cooling fan power supply

Plenty of modification potential with this power supply. I’ve got a small list of easy ones that I think I’ll make:

  • Replace the key with a regular switch
  • Switch out the banana plugs for 5-way binding posts and Powerpole connectors
  • Replace the fan with a quieter one

This seems to be a pretty sturdy power supply designed for the harsh environment of a high school lab. Everything inside looks to be in pretty good condition.

An Instructograph

While I was rummaging around through the club’s storage room yesterday, I came across an old Instructograph machine. I’m not sure how old this particular unit iss, but it looks like it has definitely seen better days.

Instructograph label
Instructograph label
Instructograph
Instructograph
Instructograph
Instructograph

It’s a paper tape based Morse code trainer with the Morse code encoded as holes in the paper tape. Along with the Instructograph were nine tins containing other tapes. Seven of them were rusted closed so I didn’t try to force them open. A couple were left open, including the one already on the Instructograph.

Instructograph tape tins
Instructograph tape tins
Instructograph tin
Instructograph tin
Open instructograph tin
Open instructograph tin

The Instructograph is essentially just an automatic straight keyer with an audio oscillator. As the paper tape moves between the contacts, the key is closed where the dots and dashes are punched out of the paper and generates the tone. The tapes are double-sided, so when you finish playing one, you just flip it over, thread it back onto the machine and play the other side.

Instructograph contact switch
Instructograph contact switch

I think the tape speed would have been controlled using this lever on the panel.

Instructograph speed control
Instructograph speed control

No idea if the Instructograph still works or what kind of condition the innards are in. The paper tapes are in somewhat delicate condition and I’m not sure if they’d hold up to much playing anymore if the Instructograph did work.