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.
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.
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.
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.
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).
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.
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.
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.
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.
I think the tape speed would have been controlled using this lever on the panel.
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.
The special event station for the Yorktown’s 75th commissioning anniversary went fairly well. Operations started off with one of the club members operating the Waterway Net on 40m from the club room, and then we got set up to start calling on 20 m. I spent a couple hours or so working stations on 20 m, moving around occasionally because of QRM. Many stations were coming in pretty loud and clear, although at times the fading got a bit deep.
We tried to move down to 40 m after noon, but got a report that our audio had a lot of RF noise in it, so we spent some time trying to figure out where it was coming from. We ended up narrowing it down to a few culprits: noisy laptops and a noisy power supply built into the FT-897. Something we’ll have to troubleshoot further.
We ended up spending the rest of the afternoon up on 20 m doing a mix of SSB and digital, but with storms moving in, there were loud static crashes all over the place, and we only made a few more contacts. With the band dead, storms getting closer, and a tornado watch issued by the weather service, we decided to call it a day around 3ish.
Finished the day with 55 contacts in the log. Not bad for a few hours of casual operating.
Band Mode QSOs
7 LSB 10
7 PSK3 2
14 OLIV 1
14 RTTY 5
14 USB 37
Total Both 55
Even though tomorrow is the actual day of the USS Yorktown’s commissioning, I thought I’d spend the afternoon in the club room activating WA4USN and get a few more contacts in for the special event. I was joined by two other hams for the afternoon.
Things didn’t quite go exactly as planned, but still went fairly well.
After spending some time figuring out the Yaesu FT-897 that was sitting where I expected the Kenwood 570 to be, I started calling CQ on 20 m. After a few calls, we (WA4USN) got a call over the repeater from a ham at a radio station set up at a nearby Boy Scout camp asking if he could put some Cub Scouts on the air with us for the special event.
Always a good thing to get on the air with Scouts, so we talked with a group of Cub Scouts (Webelos) and then got back to HF. Spent some time calling, and then another call on the repeater with another group of Scouts. Rinse and repeat.
After the third group or so, we decided to just give up on HF and spent the rest of the afternoon talking to Cub Scouts (I was too lazy to break out the headphones).
So even though there were no HF contacts today, I still consider it to be a pretty good day on the radio. Talked to 21 Scouts in total, mostly Cub Scouts. Many weren’t terribly talkative, but a few were downright chatty. Some of them learned about the Yorktown. All got exposed to radio and it seemed to have generated some interested at the camp.
I was using it to look at the output of one of my EtherkitSi5351 breakout boards when it made a high pitched “pffft”, the waveform disappeared and a bunch of indicator lights came on.
Haven’t opened it up yet to see if I can spot anything wrong. The scope still turns on, but there’s no display. The indicator lights behave like the scope is working, but there’s nothing on the CRT. That could be a good sign.
Will be a while before I have some time to poke around the innards of the scope.