Heathkit GR-25/295 thermistors/vdr

[Phil]

Hello to all. I am trying to bring back to life a Heathkit GR-25. After replacing the CRT, which had black spots around the edge of the screen and wasn't in the best of shape with a 25ajp22 both of the thermistors in the power supply burned up. I can't see how this is related to the CRT replacement, but at any rate I have to find replacements. The schematic lists one of them as 120 ohms cold and either 1.5 or 4 ohms hot depending on which schematic you believe. It probably doesn't make any real difference. The one in series with the degaussing coil doesn't have any information at all and the parts list only gives Heath's part numbers and no specs. Was this set based on a Zenith or RCA design? I find several made or packaged by Workman on eBay, but they don't give any information except various manufacturers part numbers they were designed to replace. Does anyone know which FRT number is correct for this set?

[Electronic M]

Unless the old CRT tested bad it was probably savable...There is a sheet of safety glass glued (using transparent glue) to the face of the CRT that acts as implosion protection...The glue degrades over time and loses its transparency, starting at the perimeter of the screen and progressing inward, forming what TV collectors call a CRT Cataract. CRT cataracts are fixable and info can be found here with a search. They don't make or rebuild these tubes anymore so we ought to try to save every CRT that still has good emission.

IIRC Heathkit color sets were RCA based till Zenith bought them out in the 80's. You could probably find an RCA with a similar tube/semiconductor compliment and use a Thermistor/VDR pair from that...At least if someone here doesn't know the right number.

[damen]

Similar RCA circuits used a 107191 thermistor (about the size of a nickel) and a 116534 or 114014 varistor ( the rubber coated looking one). Since this happened after the CRT was changed, be sure the degaussing coil isn't shorting out to the mounting hardware or you'll burn up the new parts.

[zeno]

+1
What usually happens is the thermistor falls apart then the glowbar melts
down. Numbers I remember were FR922 & FRTV2 IIRC. And yes be sure the coil didnt get pinched !
73 Zeno
LFOD !

Originally Posted by damen

Similar RCA circuits used a 107191 thermistor (about the size of a nickel) and a 116534 or 114014 varistor ( the rubber coated looking one). Since this happened after the CRT was changed, be sure the degaussing coil isn't shorting out to the mounting hardware or you'll burn up the new parts.

[Tim Tress]

Workman used to sell both the thermistor and varistor in one package; that was a very common repair in the old days