I’ve updated the schematic for the power supply. Made a few corrections and rearranged a few things.
Still haven’t figured out why the outputs are behaving like they’re shorted out. Putting a my DMM across the output terminals gives me about 148Ω, which seemed on the low side to me.
A quick check of the SCR shows that it seems to be ok. I think I’ll check the pass transistors next. Looks like they should be easy enough to remove for a quick test. I should probably check the big filter caps too, although I wouldn’t expect those to be bad.
In the process of troubleshooting, I’ve removed the 6 pin connector and large capacitor (1.4 mF) associated with it. I’m planning on replacing them with Powerpole connectors. Three of them will fit nicely in the space occupied by the 6 pin connector. Just need to figure out how to secure them in place.
The nominating committee put forth their selections for the club officers at the June meeting, and at the last meeting this past Monday, people at the meeting voted for them. Since nobody else stepped forward to throw their hat into the ring, the officers selected by the nominating committee were all elected by acclamation. Of the officer positions, the only new person was the President (me).
I’ll start my new job with the August meeting. It’s a bit of a higher profile position than I’m used to taking, but I’m looking forward to serving the club as President as the club heads towards its 50th anniversary in a few years.
Off I went to the last remaining Radio Shack in my area (a franchise store, also known as Hurricane Electronics) to see if I could find some fuses and a replacement lamp. Found some replacement fuses easily enough (35V, 20A), and much to my surprise, replacement bulbs that were the exact same style as what was already on the power supply.
Replacing the light was easy enough, but took a bit longer than expected. The original pair of wires for the light kept breaking when I tried to put the light back into place, so I ended up just replacing the two wires with some 18 gauge stranded wire I had. Once the light was back in place, I plugged the power supply in and on came the light. Yay!
Then I replaced the fuse, turned it back on and was greeted with the meter telling me there was 13ish volts. With my DMM, I read 13.3 V DC at the meter.
I tweaked the pot at the control board to bring it up to 13.7 V DC.
So it looks like the only problem with the power supply was the blown fuse. Now to see how it works with a load applied.
With the power supply schematic mostly done (I need to make another pass through to check that I got everything right), I decided the power supply needed a new input plug.
The power supply came with a two prong plug and a smaller two prong socket for power input. At some point someone had soldered a regular two prong power cord to the plug, which I quickly removed (mostly to get it out of the way).
The smaller socket (the round one on the right in the image below) looked like it might have been something standard decades ago, but didn’t look like anything I recognized.
The plug and socket both came out, and I dug out an old three prong power cord from the junk box. After spending some time figuring out how to connect things, I wired in the power cord.
Inside I used a terminal block to connect the power cord with the wires that used to run from the original plug.
Ground on the power cord got tied to the chassis, while the neutral line went straight to the transformer, and the hot line to the power switch.
Plugging it in and pushing the power switch made the transformer produce the characteristic buzzing sound, but it looks like the power indicator lamp is burned out. 23.2 V AC measured on the output of the transformer, which seemed reasonable. No smoke released, which is a good sign.
Now that I can get power into the power supply, I can start figuring out what works and what doesn’t.
One of my friends from the photography meetup I’m in messaged me and asked if I’d be interested in an old radio he was helping a friend of his sell.
I’m now the owner of a Hammarlund HQ-100 receiver that powers on, but will need a fair bit of restoration work.
I even got a speaker to go with it.
It’s a bit of a heavy beast, but not quite as heavy as it looks. Undoing two screws let me slide the cover off to look inside.
There’s a fair bit of dust and corrosion on the components, but except for the band spread dial, all the controls seem to work. Not sure how the radio spent the last few decades of its life. I’m pretty sure I’ll have to replace a few components, especially the mechanical bits. Smells like the previous owner might have been a smoker, but it’s hard to really tell.
This is going to be a fun restoration project to work on. It’s going to take me a while, but I’m going to enjoy working on it.