Heathkit GRN-900-21 - Videokarma.org TV - Video

msimendi · #1 09-12-2009, 01:07 PM

I got this set from a guy at work who's wife wanted it out of the house. He was delighted I took it as it took him a year to build it back in '73. He said it would have broken his heart to put it on the curb. It wasn't working; it kept going into overcurrent as I brought it up on the variac. It turned out to be a blown diode in the 155V rectifier circuit. Easily found replacements at the shack.

I will replace the electrolytics and fuse all the supplies, but looks promising so far. He gave me the full set of manuals which will be a big help.

freakaftr8 · #2 09-12-2009, 04:18 PM

Awesome! Another Heathkit up and running, I have a GR-250 1967 up and running too but needs attention. That looks to have a beautiful picture, curious though, is that a delta or inline gun CRT?

radiotvnut · #3 09-12-2009, 05:09 PM

And is it tube or SS? A friend had a similar 25" delta gun set that was SS except for the HV rectifier.

msimendi · #4 09-12-2009, 05:28 PM

It is SS with 1 horizontal output tube.

I don't know if it is single gun or delta, how do you tell? Picture tube is 25VDP22.

Although maybe not evident from that screen shot, I see now after watching it awhile that the brightness is not as it should be even on maximum setting. It gets hard on the eyes after awhile; darker colors are all black. Maybe the CRT is going. What tester can I use to test the CRT? I have an old B&K 440 I use for B&W CRTs but I don't know if that will work here. Can these CRTs be "cooked" at higher filament voltages, as is done on B&W CRTs? How about rejuvenation with a Beltron tester?

msimendi · #5 09-12-2009, 05:29 PM

I mean high voltage rectifier tube.

freakaftr8 · #6 09-12-2009, 05:58 PM

Sounds like a delta gun to me. The difference is a delta gun is composed of many fine dots placed together on the phospher. An inline gun uses small rectangular openings. On a delta gun CRT the guns themselves are placed in a triangular pAttern where an inline gun the guns are all paralell with eathother. Your brightness issue may be a few things. The easy way to make it brighter would be to turn up your kine bias or crank up the drives. You could have a weak tube but it could be a number of things.

freakaftr8 · #7 09-12-2009, 06:02 PM

Oh and yes color CRTs can be cooked at 8v too. But your CRT tester may not have the color harness. It's possible that if the CRT hasn't been used for a while it may get brighter all on it's own eventually. The getters are probably "dusty"

bgadow · #8 09-12-2009, 11:07 PM

I like all those knobs-more to tinker with! Great save...you'll make the guy who built it proud.

radiotvnut · #9 09-13-2009, 12:46 AM

I'll bet that set uses the same chassis that my friends' TV had in it. The yoke went bad in his set and the CRT developed cataracts. He threw out the insides and stuck a newer TV in the cabinet and ended up selling it later on.

If you need to rejuvenate this tube; get a B&K 467, 470, 480, or 490. The lower models have a rather crude rejuvenate function that might literally "blast" your CRT. From what I hear, the later model Sencore's (CR70) and the Beltron models are good units. You should be able to pick up a good CRT tester for under $100 if you look.

msimendi · #10 09-13-2009, 05:13 PM

freakaftr8 - I'll use it for a while and see if it improves on its own like you said. It has been sitting unused for over 10 years. Thanks for the info that the CRT can be cooked at a higher filament voltage if need be.

radionut - thanks for the suggested CRT testers.

bgadow - yes the guy was already thrilled when I sent him a B&W screen shot, and should be even happier when he sees the color shot tomorrow. He can't believe I got it going.

The reason I want the CRT fully bright is I intend for this set to be my daily driver. I'll keep you posted.