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Heathkit GR-900 Build Thread!
I just scored an UNBUILT Heathkit GR-900 25" color TV kit at the NJARC auction yesterday, and I am going to document the build process here on VK. I have always wanted to assemble a "real" Heathkit TV, after building countless smaller heathkits over the years. I did build one of the mid 80s TV kits for a family friend while I was in high school, but those were simply unassembled Zenith System 3 sets, with all the modules prebuilt, taking away most of the fun.
Anyway, this set was part of a Bell and Howell/DeVry TV Repair training course, and in addition to the 7 (!) standard Heath assembly manuals, there are 5 manuals of "Color TV Experiments" to be performed on various modules and subassemblies during the build, but they require additional parts and an experiment console which didn't come with the set. So I will be building the set in the straightforward manner as the normal Heathkit customer would. This is an early 70s vintage set, which is 100% solid state with the exception of the HV rectifier and CRT. It is built on multiple plug-in PCB modules, which are then plugged into a vertical metal chassis. It was apparently bleeding edge stuff in the day, with a varactor UHF tuner and automatic fine tuning. There are several integrated circuits used, in addition to the dozens of transistors. The tuners, IF, AFT and HV section come preassembled and aligned at the factory, but there is a LOT for the builder to do, unlike their later sets. Several boxes of this kit had already been opened and dug through, so I started with a COMPLETE inventory to see if everything was still here. On the plus side, the original purchaser apparently received a double shipment on one package, so I have a spare VHF tuner, as well as spares for the IF module and all the parts to build up additional Chroma, 3.58 oscillator, and AGC/Sync modules. Also found was the optional GRA-900-6 ultrasonic remote control kit! On the downside, I am MISSING the audio and vertical output transformers! I have posted a want ad here on VK, as well as the Yahoo Heathkit list looking for these, and if anyone can help here, PLEASE let me know. It would be a shame for this set to never run because of 2 missing parts. Hopefully, replacements can be located for these, or I am going to end up with a handbuilt electronic doorstop. Another issue is that the NOS RCA 25VABP22 was apparently stored in a damp location that rotted the box away and may have caused a cataract around the edges of an otherwise virgin CRT. Hopefully, it will not be too visible once the CRT gets installed into the mask. A cataract removal or CRT replacement could always be done if the results warrant it. Anyway I will be getting underway with the build tonight. Because Heath intended even their most complex kits to be buildable without anything more than hand tools and a soldering iron, the first thing that the TV builder needs to assemble is the "Troubleshooter", which is a simple 5 range VOM used for testing the rest of the set as the build progresses. It is then installed inside the set (along with a built-in Bar/Dot generator) to be used for future troubleshooting/adjustments as needed. Next up--Building the "Troubleshooter"! Last edited by N2IXK; 05-14-2016 at 08:49 PM. |
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I had to scrap a 20" heathkit tv a few years back...because the cabinet had gotten RUINED In my old garage. it was SS, with SCR deflection--maybe a HV rect tube--all else modular SS. I kept the tube and chassis, MAYBE the tuner. Know where the chassis is right now. it DID use a large TO-66 audio amp, IIRC. SO--it must have an output transformer. Pretty sure it also had one large vert transistor for the V-out..but will have to look again...
I just KNEW...there would come a time...someone would be needing some part from it... |
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I just looked at an RE magazine from late 1970--my set is there. Looks like a GR_270, 20 inch version. it DOES use a v-out transformer, and a TO-3 transistor mounts on the chassis right above it. is your chassis like this.
Also--the A-out transistor is on the left, above the power tranny, there are a pair of transsitors, but I do NOT think both of them are for audio. |
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Definitely sounds similar to my set. I have a lead on a junker chassis from a local VK member, which I am going to look at in a couple days. If that doesn't work out, I will let you know. Thanks!
I am amazed that within a couple hours of posting, I now have THREE potential sources for these 2 obscure 40+ year old parts lined up! Thought I would be looking for months. The power of the internet.... Last edited by N2IXK; 05-01-2016 at 09:50 PM. |
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After about 15 years on the net...I wonder....just HOW we did it before then. Me, mainly the old "tradin' post" paper--I found a lot of things through that...and of course, word of mouth and the curb...from the beginning.
This tv came from an auction--in about '93, that I did NOT attend...but I ended up with this set form the guy who DID attend. IIRC...it DID work...and had the cabinet not been hopeless...i would still have the complete set. Buty..water and rats do take their toll... |
Audiokarma |
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Since Heathkit used RCA's SCR sweep I wonder if they also copied the
vert out from one of the early XL's ?? A lot of RCA in them. The audio should be easy, if they used the high collector voltage transistor one from a Zenith hybrid should work fine. 73 Zeno |
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Quote:
jr |
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Back to the build! First off, a big thanks to Tim for supplying replacement audio and vertical output transformers for this set!
Got started on the first PCB assembly, the Sound module. This module implements essentially the entire audio section, with the exception of the chassis mounted power output stage. It contains 2 transistors, one IC, and a ceramic 4.5 MHz IF filter. Most of the modules in this set use tubular contacts on the PC boards, which mate with pins mounted on the chassis. Construction begins with the installation of these contacts, which insert into 2 rows of square holes along the top and bottom edges of the board. A plastic alignment jig that resembles a lego block is placed over each row of contacts, the contact tabs are bent over to contact the foil pads on the board, and the tabs are soldered down to the board. Once the soldering is complete, the alignment jig is removed, leaving a properly spaced, straight row of contacts. The kit provided a long length of 3/16" diameter black PVC tubing, which is cut into short lengths and slipped over the contacts to provide protection against shorting adjacent pins. The provided tubing was pretty sticky and in poor condition from plasticizer breakdown, so I substituted some red heatshrink. The board is then stuffed in stages, starting with a jumper wire, followed by the resistors, IC and transistor sockets, capacitors, inductors, and the IF filter and coil. Finally a short 2 -pin cable is attached, and the semiconductors are installed in their sockets, completing the module. Next up: The Luminance module. |
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More pics:
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Never having built a kit myself, just luuuv seeing this one go together. Built a few projects from the schematics Heath used to put in their catalogs, though. They all worked, too.
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Audiokarma |
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I still think there's a bunch of miswired freaks out there wishing death upon you because god forbid you assembled a heathkit set.
What's the point of owning the kit if you don't want to assemble it? |
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Wow! I never saw the schematics in the catalogs... I only got into Heathkit in the 1970's and '80's however. Were these schematic laced catalogs earlier than that?
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What Heathkit list? I'd love to go there.
WANTED: unbuilt or built, alive or dead, Heathkit GR-180 TV WANTED: Alive, very alive only, correct picture tube for above. |
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The GR-900 build continues..
Next up, the luminance module. This module incorporates the standard luminance circuitry found in any color set, in addition to the dot generator circuitry used for the convergence setup. The dot pulse generator circuitry incorporates a relaxation oscillator based on an NE-2 neon lamp, followed by some wave shaping circuitry. Testing a sample of the original electrolytics showed that most of them were acceptable, but a few showed borderline high ESR, even after reforming for a few hours at or near rated voltage. I decided to replace all the small electrolytics as cheap insurance against problems. The 2 large twistlocks for the main chassis seemed to reform perfectly well, and will be used. Replacing the electrolytics on the smaller modules allowed me to get radial lead types where needed, rather than the rather ugly vertical mounting of axial caps that the board layout originally called for. Next up--the Video Output board. |
Audiokarma |
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