RCA T8-18 - Printable Version
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RCA T8-18 - mikethedruid - 09-01-2019
Today I cleared off my bench from the debris from restoring that little un-named cathedral radio, and put on my next project, an RCA T8-18 I bought months ago. It looks like it has not been touched in years. I haven't pulled the chassis yet, but from what I have been able to see so far, the only modification done to it was putting on a masonite back with holes in a 1 inch grid, and drilling one hole larger so that they could slip a much more modern plastic insulated line cord through it and splice it to the cut off end of the original cloth covered line cord. I guess whoever once had it had cats or small kids and didn't want them getting into the back of the set. Fortunately I have downloaded all the RCA service manuals from 1932 to 1948 in 4 volumes, so I have good documentation to go by for this restoration.
[Image: https://66.media.tumblr.com/dfc64aba12b012b8b64f9d94b7f9b859/tumblr_px6krs8use1s2snqvo1_r1_1280.jpg]
[Image: https://66.media.tumblr.com/806b6df271cf93a8857c026410318b47/tumblr_px6krs8use1s2snqvo2_r1_1280.jpg]
[Image: https://66.media.tumblr.com/2b0da370cc6e2a8e3015516b6209149d/tumblr_px6krs8use1s2snqvo3_r1_1280.jpg]
The grill cloth seems in VERY good condition. That's a plus. The cabinet is pretty good too., no big repairs, just light refinishing.
RE: RCA T8-18 - mikethedruid - 09-02-2019
I pulled the chassis. It looks pretty much unmolested. There is also enough room to work, thank goodness, and not too many paper caps to replace.
[Image: https://66.media.tumblr.com/50e23eb0fbb3c238dfac733f528ad413/tumblr_px6uu40d6R1s2snqvo1_1280.jpg]
RE: RCA T8-18 - Ron Ramirez - 09-02-2019
I like that set. I compared its schematic to the T7-5 and I see they are basically the same; RCA just added a tuning eye tube to the T7-5, changed the rectifier from an 80 to a 5Z4, and put it all in a different cabinet.
I own a T7-5 and it is a great little radio.
Count on replacing at least one, and probably both, of those Candohms. It seems that where Philco's weak point is coils, RCA's is Candohms.
RE: RCA T8-18 - mikethedruid - 09-02-2019
Today I placed an order for all my condensers. Last night I ordered cloth covered line cord to replace the original. I have a question for anybody who knows, before I start playing with things, in the picture of the bottom of the chassis there is a silver colored item in the very upper left hand corner of the chassis. It appears to be some kind of condenser, but I'm not sure. I haven't traced it on the schematic yet. Does anybody know what this part is? Please let me know, it may save me some time.
RE: RCA T8-18 - Ron Ramirez - 09-03-2019
You mean here (red rectangle)?
That is a capacitor encased in a metal sleeve, .01 uF I believe (the schematic will tell you). You can gut it and install a new cap inside the metal sleeve, which is what I would do as RCA wanted that capacitor shielded for a reason.
RE: RCA T8-18 - mikethedruid - 09-03-2019
Thanks a lot Ron ! That is what I was wondering about. I will do exactly that. Thanks for the advice.
RE: RCA T8-18 - mikethedruid - 09-03-2019
I traced out that condenser, and it is indeed a .01mfd on the schematic. Not only is it shielded, but the line running from one end of it to the volume control is also shielded, probably to keep noise out of the audio circuit, hum, that sort of thing. The other end ties into the AVC circuitry off the 2nd detector. My word they did a sloppy job assembling this thing, nothing really wrong, but pretty sloppy really. At least it isn't TOO crowded in there. I suppose one reason it appears sloppy is to keep all the component leads as short as possible in the RF and IF sections, which is actually normal practice. Also, some of these old BED resistors don't look like they are correct in value, although original. I'll just have to look carefully at them all and test them, and try to sort it out. Hopefully they will be close enough so I won't have to replace any. Philco seems to have done a neater job, and used resistors that were marked more clearly. At least this one isn't as bad as that 18T I worked on a while ago which had rubber covered wire with melting insulation, literally, turning to sticky goo, and crowded as all get out.
RE: RCA T8-18 - mikethedruid - 09-05-2019
My cloth covered line cord arrived today. I need to go down to the auto parts store and get a rubber grommet for the hole before I install it. My condenser order got held up by USPS for some reason, but is back on its way., maybe because of the storm. Who knows? I checked out the two candohms in the set. One, the 3 section one, is OK. The other, the two section, both sections are bad. Ordered power resistors to replace them today.
RE: RCA T8-18 - mikethedruid - 09-05-2019
Went to the auto parts store to get the grommet. Things sure have changed over the years. I remember when they used to carry them in drawers sorted by size, and you could buy just the one that you needed. Now you have to buy them in an assorted pack with a bunch of others that you will probably never find a use for. I installed the power cord. The wire I ordered turned out to be a royal bear to strip. Inside the cloth outer covering it was a round plastic line cord that was hard to cut through to strip the outer jacket without nicking the insulation of the two wires inside, and then was a bear to pull off the inner wires. On top of that the color coding was the European blue and brown, not standard U.S. black and white. I used blue for hot and brown for neutral which I remember as the way it goes from years ago when I was working. Now I just have to wait for the rest of my parts to arrive.
RE: RCA T8-18 - Eliot Ness - 09-06-2019
Mike, the last cloth covered wire I bought was that round stuff also, and yes it was a bear to strip. I wound up buying something like these these:
https://www.amazon.com/gp/product/B006962PLG/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Which are the same as the Color Cord 3000 used in the following video:
https://www.youtube.com/watch?v=w1_elD4pbqA
It did make stripping that round wire much easier.
RE: RCA T8-18 - EdHolland - 09-06-2019
Mike - the Euro code for mains wire is :
Green & Yellow for Earth,
Brown for Live
Blue for Neutral
UK folk resented and derided this choice being dictated to us for years. Few now remember Green for earth, red for live, black for neutral. Red-Green colour-blindness could be problematic with this system.
I still have to think twice with the US system of white and black. (But I ALWAYS check)
Cheers
Ed
RE: RCA T8-18 - mikethedruid - 09-06-2019
The standard U.S. system is black for one side of live, white for neutral return (grounded), red for the other side of live, and green for grounding. Here black is 1/2 of the 220 circuit, with neutral being center, and red the other 1/2 of the 220 circuit, red and black being inverse phase from each other with regard to neutral. I could never remember the euro colors, and had to ring out the line cords we got in to remember what blue and brown went to. Fortunately we usually got cords with proper color code. The U.S. code actually goes all the way back to Edison, who used direct current. Red was 120 volts positive with regard to neutral. Black was 120 volts negative with regards to neutral. He used the three wire distribution system to save 25% on cable costs over using a 4 wire system, and when the systems were converted to AC, they still used that color coding and system.
RE: RCA T8-18 - mikethedruid - 09-06-2019
I've been busy. I have finished replacing all the paper condensers, and all the carbon resistors. I have to wait now for the arrival of my electrolytic condensers and the power resistors to repair the bad candohm.
[Image: https://66.media.tumblr.com/db21c7f85af90cd3ec5a8e0cc5e025e6/tumblr_pxfur7xB871s2snqvo1_1280.jpg]
RE: RCA T8-18 - Jake Blake - 09-07-2019
Nice !
Things always open up a little with the new stuff.
RE: RCA T8-18 - mikethedruid - 09-09-2019
Well, today I got around to testing the tubes. Oh my, oh my! Lots of bad tubes. I tested them on both my testers. Bad 6E5 (expensive if local !) bad 6F5, bad 6F6, bad 6H6, bad 6A8. Just dropped a lot of cash on tubes. I had some in GT type, but these are in an RCA, so I had to order the metal type since this radio needs them for shielding. Oh well, that's life when you restore antique radios. I admit, I ordered doubles of a lot of tubes. There was a deal on Soviet made 6E5 tubes, so I ordered 3 of those which will ship in from Bangkok, Thailand; I also ordered 1 from a USA source so I'll get it a little faster. Those are magic eye tubes.