Heathkit GR-900 Build Thread!

[Electronic M]

Wish I could find a unbuilt tube Heathkit TV. That would be a fun project.

[WISCOJIM]

Originally Posted by Electronic M

Wish I could find a unbuilt tube Heathkit TV. That would be a fun project.

They're still around, sometimes right under your nose. Got my latest one at the ETF convention this year when the rest of you guys were off to lunch! My van was packed to the roof on the return trip. This one included the multimeter and tube tester kits with it.

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[rca2000]

Did not see it..or perhaps I too would have bid.. But I got enough from the ETF this time... INCLUDING the BW set in my avatar...certainly NOT disappointed !!

[N2IXK]

All of the ICs in this set were (or went on to be) industry standard stuff of the day. Mostly Motorola and RCA linear ICs, most of which were second sourced by other vendors, and were available from ECG, SK, or NTE at least at one point. Same types of chips that started showing up in other manufacturer's sets of this era.

This kit had already been unpacked and partially gone through, and I received it in 2 large boxes, 4 smaller boxes (one for the remote control option), and of course the CRT carton. One of the smaller boxes was apparently a duplicate shipment. Not sure if the training classes shipped the whole kit at once, or in multiple shipments to each student.

Anyway, the build continues on board by board. My best friend and her daughter were over last weekend (Daughter needed help with replacing a fuel pump on her car that we had diagnosed as bad a few weeks earlier), and she was asking about all the boxes of parts down in my basement shop. I told her that I was putting together a DIY TV kit, and she was intrigued with the idea of building your own TV. Showed her a few of the modules I had been working on, and she was so interested in it that I gave her a few quick lessons on soldering, and turned her loose on the Chroma board (which was one of the ones I had a spare for from the duplicate shipment). She did an AMAZING job putting it together, and wants to drop by again to do some more on the set, before I finish it all. By the end of putting the board together, she was already starting to learn the resistor color code, too...

The Chroma, 3.58 MHz oscillator, and AGC/Sync modules all went together that afternoon. Here's some pics of the finished board, plus a shot of my soldering student in action....

Up next, Vertical Oscillator, Horizontal Oscillator, and Pincushion modules....

[N2IXK]

The last 3 of the plugin modules are completed and ready to go. Construction is much the same as the previous ones. Here we have the Vertical Oscillator, Horizontal Oscillator, and Pincushion modules. I have been replacing the electrolytics with modern equivalents as I go along.

I have tested a random sample (maybe 25-30) of the resistors during the build, and have found the values within tolerance (some just barely). Solderability of the boards remained very good through 40 years of storage, and almost all of the components have been perfectly usable right out of the box, as well. Some of the diodes which had silver plated leads had a bit of tarnish on them, but it wiped right off. The CTS brand trimpots were the only major soldering problem, with the wiper terminals refusing to take solder until I heavily wirebrushed the terminal (removing whatever the plating was and exposing the brass underneath). Not sure what the plating is, but it develops a thin brownish/purple tarnish that solder flux does nothing to. The end terminals of the pots are just fine, having what appears to be a tin/lead coating.

The final pic here are all 9 of the modules completed so far. Next up is the convergence panel....

[N2IXK]

The convergence panel is the largest PCB so far. It houses the usual array of wirewound pots and coils used for the dynamic convergence adjustments. It is mounted on a small subchassis, along with the UHF tuning presets and several secondary/service controls. It uses 6 silicon diodes rather than the traditional selenium convergence diode assembly found in most commercial sets of this era.

The UHF preset tuning assembly is similar in concept to the preset tuning panels that became common a decade later in early VCRs. It consists of a carbon film resistive divider, with 12 separate adjustable sliders to set the varactor tuning voltage for the desired UHF channels.

Most of the wiring comes in the form of prefabricated harnesses which are soldered to the various points on the subchassis. The 3 convergence magnet assemblies that go around the CRT neck are attached to one of these harnesses, and the other harnesses have connectors that will get plugged into the rest of the chassis at final assembly.

The convergence panel completes the first of the assembly manuals. Before moving on to the next manual in order, I am going to go through the assembly of the optional remote control, which has its own manual, separate from the ones for the set itself. The next post will deal with the assembly of the remote control transmitter...

[N2IXK]

Got started on the GRA-900-6 remote control, by building the handheld transmitter unit.

Unlike the Zenith type mechanical transmitter using ultrasonic chimes, the Heathkit design is electronic, consisting of a very simple 1-transistor Hartley oscillator, driving a small ultrasonic transducer. 8 separate ultrasonic frequencies can be generated by pressing each end of one of 4 rocker style buttons. Functions include on/off (which can also select one of 3 audio levels), UHF/VHF select, channel up/down, color up/down, and tint red/green. Each function button contact switches one of 8 precision (2%) silver mica caps into a single transistor oscillator circuit. The circuit is powered by a standard 9V battery.

Construction was pretty straightforward, with only 2 age-related issues. The 16 small brass rivets used for the board mounted switch contacts were pretty heavily tarnished and needed a good cleaning in order to be soldered onto the board and make reliable contact with the rocker leaf switches.

The other problem was that the provided foam tape had completely dissolved into sticky goo that was all over the bare PCB. Luckily it cleaned up well with IPA, leaving the board unharmed. The foam tape was replaced with a modern equivalent weatherstripping tape, and is used to cushion the battery and ultrasonic transducer inside the 2-part plastic housing.

For some reason, the remote transmitter and receiver PC boards are phenolic based, rather than the nicer epoxy glass ones in the rest of the set.

After finishing the remote transmitter, I installed a battery to see if it worked. I tried plugging the TV receiver microphone into a scope (it has an RCA plug cable attached) to see the signal, but saw nothing at all. A quick look at the receiver schematic shows that the microphone needs a 200V or so bias voltage which the receiver provides. I connected my scope probe right across the transmitter output leads, and got nice strong sinusoidal signals right at the transducer, with a different frequency for each button pressed, so the transmitter seems to be functional.

Up next, the remote receiver and the first hints of trouble ahead?