speedy_w_beans 4272 Posted November 26, 2014 So about a month ago I had mentioned some cool older equipment I had inherited from my dad (http://www.tamiyaclub.com/forum/index.php?showtopic=74617), and with the Thanksgiving break I now have a little time to dig in. Between the air compressor and this Heathkit receiver, the receiver definitely has more sentimental value to me. It's great to know the previous owner so well, check out his workmanship, and do some minor repairs before putting it back into service again. From what he had told me, it sounds like two light bulbs in the display panel are burned out, one segment in one of the numeric displays is possibly burned out, and maybe one or two potentiometers need some contact cleaner sprayed in them. Here's the front of the receiver. There are four main control knobs including tuning, mono/stereo, input selection, and volume. Flipping the lower panel down reveals several smaller jacks, buttons, and knobs including headphones, speaker enable, high/low filters, bass, treble, balance, tone, loudness, squelch defeat, blend, Dolby, tape monitoring, and tape dubbing. Both sides have beefy heatsinks and wood trim. The rear panel includes switched and unswitched power, antenna inputs, speaker outputs, phono/aux/tape inputs, tape outputs, preamp outputs, and power amp inputs. It's great to have the original assembly manual, the complete schematics, and reference illustrations. All the parts are listed, all the calibration procedures are there. Servicing this should be entirely possible both now and in the future. It's also really nice to have an original copy of Popular Electronics from 1977 with a review and test report on this exact receiver. Sometimes I tell one of my younger co-workers how he's really missed out on the golden age of electronics, in my opinion. The 1970s was a great time to be interested in electronics because a hobbyist could get his hands on a wide variety of technology (core memory, nixie tubes, vacuum tubes, transistors, ICs, LEDs, etc.) and build a lot of things himself. It wasn't all integrated in a single chip like many designs today! The consumer market was still trying out all sorts of new ideas instead of the steady incrementalism we see today. Vinyl and tape were in full force, and CDs were just around the corner. When I was a kid in the 1970s, I used to borrow Popular Electronics magazines from the local public library to read and absorb as much as I could. I think between the library materials, my dad's profession, watching him build models and electronics at home, and gutting old radio chassis for parts, my path to engineering was pretty well set. Some of the latest and coolest in the late 1970s... Reel-to-reel was still a current topic... For about $1900 you could have an 8" floppy drive, CRT monitor and keyboard, and CPU with 4k (yes, 4k) of memory... There was always something new to build with each month's issue of Popular Electronics... So I'm ready to dig in... More to come soon... 1 Share this post Link to post Share on other sites
mongoose1983 3335 Posted November 26, 2014 What a FANTASTIC piece of Hi-Fi equipment! Looks minty, and I don't think it would be too hard to solve the problems to make it work as good as back in the very good old days. Again, what a great receiver. Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted November 26, 2014 Last night and this morning I dug into the receiver. I just hooked up some bookshelf speakers and a makeshift antenna, and it all came to life as expected. I was curious about its power and sound quality, and started turning up the volume. The kids came into the kitchen to tell me to turn it down. Imagine kids telling parents to turn down the volume! Right away I could see the bottom segment of the rightmost digit wasn't working, and the 2CH (stereo) indicator wasn't working either. Going through all the controls I also found the AUX indicator didn't work, and the only really noisy control was the left-right balance adjustment. Time to get to work... The top cover slides off after removing three screws from the top edge of the rear panel. Here you can see the overall layout of the receiver; it's completely modular. There's a tidy wiring harness routing the signals from board to board. I needed to remove the front panel to get access to the display and indicators. Each block of wood came out with a single screw; the second screw simply slides into a slot in the chassis. There were four screws holding the corners of the front panel to the main chassis, and then there were five more screws securing some bottom plates to the front panel and main chassis. I had to unplug one harness to provide enough slack to lay the front panel face down on the table. Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted November 26, 2014 The frequency/indicator/meter assembly is held in place with four self-tapping screws that thread into the front bezel. I was keenly aware of the age of these plastics (37 or 38 years) when I was working with these screws. Front bezel... You can see the colored areas where the indicators and meters show through. Here's the front indicator assembly. The LEDs are socketed and the lights have their own buckets. So the first item I worked on was the frequency display. I didn't know if the LED segment was burned out or if one output from the driver chip was burned out, but since the LEDs are socketed I figured an easy way to test this is to just swap the leftmost LED display for the rightmost LED display. Since the leftmost display only shows a "1" for FM radio stations higher than 99.9, or AM radio stations higher than 990, the bottom segment on that module should have zero wear and should be good. And, since the vertical segments in the rightmost module are still good, it could still serve as the leading "1" indicator even if the bottom segment is broken. I made the swap, and it turned out the LED segment was bad (not the chip), and everything worked perfectly with just swapping the two modules. Easy! Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted November 26, 2014 Next up were the indicator lamps. My dad actually had a few spare bulbs from a purchase he made in 1993; they came with the receiver. The spare bulbs came from a Radio Shack store not far from where he lives, and he actually saved the burned out bulbs as reference for replacements. That particular store no longer exists, but the exact same part number is still found on Radio Shack's web site today! In the center set of six bulbs, I've pulled the top left (2CH) bulb and the middle right (AUX) bulb for replacement. These are just connected to a few terminal strips; this is easy work with a soldering iron. As you can see, the original 2CH bulb burned out long ago; now the replacement has burned out. A few other bulbs have been replaced over time too. New bulbs soldered and installed... Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted November 26, 2014 I've added to the burned out bulb collection... Reassembly of the front panel to the main chassis was the opposite sequence for removing it. Slip the front panel into position, install five bottom screws, install four corner screws, install the wood trim blocks, connect the wiring harness, and install the control knobs. Fixed! Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted November 26, 2014 The two last things I wanted to do was blow some dust out of the chassis and clean the balance control. For the dust I just used a small air compressor and air nozzle to chase the dust bunnies out. Considering this receiver sat on my dad's shelf for nearly 37 or 38 years, it was amazingly clean inside. The only thing I can figure is he must have had another component stacked on top of it, or it was simply so secluded on the book shelf that it just never collected much dust. If I had been a little smarter I would have left the front panel of the chassis off to clean the balance control. Fortunately, the potentiometers had small holes in them that made it easy to spray them with some contact/control cleaner and a small straw. I could have sworn I had some of this stuff in the house already, but I couldn't find it. I made a trip to the local auto parts store to get some more... And while I was out, I also stopped at MY local Radio Shack and bought a few more packs of spare bulbs for the future... So now I have his stereo receiver from 1977; burned out bulbs, a spare bulb, and a receipt from 1993; and now my own stash of bulbs and a receipt from 2014. Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted November 26, 2014 Some of the cool tech from long ago... Beefy linear power supply... Ganged tuning plate capacitors... Frequency counter and digital display... Rotary switch input selector... Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted November 26, 2014 Beefy TO-3 power transistors in the power amp stage... So it's all back together and working fine. It was a fun little project. It should give us several more years of good service. I'm glad we could save a part of our family's history and pass it on in due time. 1 Share this post Link to post Share on other sites
mongoose1983 3335 Posted November 26, 2014 Excellent! I would say that's more than part of your Family's history, it's also a great stereo in its own right. Also, I always liked Advent stuff. I used to have a Dolby NR system hooked up to my Bang & Olufsen reel-to-reel deck. Too bad I let that baby go, but back then I thought I needed a Bruiser truck, LOL. Anyway, now I'm curious. What is going to be the first song you'll play through that Heathkit + Advent set-up now that you fixed it all up, Paul? Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted November 26, 2014 LOL, well, the first music I played was just a local FM station that's broadcasting nonstop Christmas music for the next month. I've taken the setup apart now and reconnected the bookshelf speakers to my Technics SA-GX550 receiver. Eventually I'll break out the Advent tower speakers and pick one of the clearest/cleanest recordings I have. The Heathkit receiver still sounds really good even with FM broadcasts. Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted September 25, 2018 Photo hosting fixed for 2amp2! Share this post Link to post Share on other sites
speedy_w_beans 4272 Posted September 25, 2018 And hey, let's throw up some documents for anyone to find via Google. Be sure to click on the images first, then right-click, and save to get the full file size (about 7MB per file). Schematic quadrants: Circuit board layouts: Share this post Link to post Share on other sites
