RCA model RC-1129 AM-FM radio chassis

[electra225]

This and its later version RC-1129A are the chassis in the big RCA table radios I have been tinkering with here lately. This particular chassis is a parts chassis I have had for probably 30 years and have never plugged it in. I robbed the dial cord and the speaker for past projects. My memory tells me it came from a broken bakelite cabinet set I got off the 'bay, but don't hold me to that. I dug it out this morning, thinking it might be in better shape than the one that belongs in my 6-RF-91.

I did a good visual inspection to make sure all the important parts were still there. This set has the same chassis as the 6-RF-91, probably from the 1948-'49 era. None of the tubes are original, date codes range from 1943 to 1961. It has GE, RCA, Reliant and Sylvania tubes in it. It has a dirty function switch, dirty RF amp tube socket, dirty oscillator tube socket. I put an 8" pincushion frame speaker I had on hand in it. I found a reason why the dial cords like to slip on these chassis. There is a pivot, in front of the speaker that was almost totally seized on this chassis. The grease on the shaft had turned to glue. I took it apart and cleaned it real well, then relubed with a dab of Phonolube. I'll worry about restringing the dial after I get the chassis sorted. I powered up on the Variac and dim bulb with the KAW. No dim bulb until the set ran about 45 minutes. Wattage started out at about 60 watts, by the time I turned it off, it was drawing 92 watts. RCA filter caps are normally really dependable, these are the exception. The filter cap can got really warm (hot) so I am going to have to replace those. It seems to be a good performer. Right now, the plan is to use this chassis in the set I'm redoing the cabinet on. I'll use that chassis as a bench radio.

[electra225]

To work on this chassis, the best way is to roll it over on its top, resting on the antenna board, then putting a thick book under the power transformer. I pulled the tubes and cleaned the chassis. So I had to work on the rigging that holds the antenna board on and restring the dial before I put it all back together. These dials are not all that hard to restring, once you get the hang of them. You just have to make sure all the pivot points are cleaned and lubed, including the tuner. Next up is to cut the can apart so I can restuff the filter capacitors.

[electra225]

I cut the can apart and replaced the filter caps and the cathode bypass cap. Everything is great there, it pulls 65 watts at 120 VAC line voltage. I was playing records, using this radio chassis for the amplifier. I ran it maybe an hour when the volume dropped and the audio got very distorted, garbled. It is the same on both radio bands as well. Something in the audio has taken a big dump. I haven't done anything to this thing in the way of replacing components outside of the filter caps. This set has the typical high-voltage value capacitor in the audio, .0018 uf @ 1600 volts. I have no idea why this radio should need a cap in the audio with such a high value. Testing and tinkering to follow......

[electra225]

Crummy buttons.....

I can't find the schematic for this set. I have a real Sams manual for it someplace. It is not in the place it should be nor in the place I looked. I'll have to find it or get another so...

What I THINK I know at this point is that there is no B+ on the plate of the 6AV6 first audio tube. There is also a noise I'll call a hum for lack of a better word, in the audio, behind the volume control, which the plate of the 6AV6 would be. When I touch the plate of the 6AV6 with my meter, the noise/hum disappears. This places suspicion on the .01 uf cap on the plate of the 6AV6. B+ at the cathode of the rectifier is 250 volts, give or take, so that is not a concern. Screen voltage on the 6V6 is close to that and I have 220 volts or so on the plate of the 6V6. I'm trying to actually troubleshoot this issue rather than just throwing caps at it and not learning anything. Replacing all the remaining paper caps is probably a good stunt, going forward. More testing and tinkering coming up....

And, just an aside......

I really like the dial cord I got from Just Radios. I got the larger of the two sizes. It is a tad "bunchy" on the shaft with the knob, but that is better than being prone to slip. The dial cord looks like it might have a "grain" to it that helps it not to slip. Easy to work with and it doesn't unravel when you cut it.

[Hi-Fi-Mogul]

I can't find the schematic for this set. I have a real Sams manual for it someplace. It is not in the place it should be nor in the place I looked. I'll have to find it or get another so...

You can see if this chassis is the same as yours in
free online 1955 Beitman's per RM:

https://www.radiomuseum.org/r/rca_6rf9_ ... 9a_rc.html

[electra225]

It is and that is the schematic I have, but have misplaced it. In fact, I have misplaced my entire RCA folder. It has the schematic for the RCA TV set I recently was working on. I had several RCA schematics, including the little RCA 45 changer I restored. I put it someplace.......

The one you linked will work while I look for that folder. I'm sure it is in the shop and in a really safe place.....

Thanks, Mr. Mogul.....

[electra225]

The .01 uf cap connected to the plate of the 6AV6 tube seems to have been the trouble. I have 65 volts on the plate now, before there was zero. This thing has an extremely hot front end for a table radio. I'm not sure it is in Hallicrafters boat anchor territory, but I got a station today I had never heard of. KXTG 1280 AM, appears to be a country station. I'll ask MR. Google to see does he know where it comes from. I'll run this chassis considerably the next few days to make sure there are no more surprises.

[electra225]

According to Mr. Bing, maybe I was listening to KXEG, 1280 out of west Phoenix. This says 49 watts, so maybe that's why I never heard it before. Says it is a Christian station, but "Ode To Billy Joe" and Elvis Presley's "In The Ghetto" is hardly Christian music.

https://radiostation.info/am/arizona/KX ... e_vignette

I can bring in a 49 watt station probably 50 miles away, but I can't even get the carrier for "The Bull" less than 20 miles away.....

[TC Chris]

Yay for tuned RF amps in broadcast-band radios, right? What is the threshold transmission power for FCC licensing, anyway? 49 watts could be produced by a squirrel on a treadmill and wouldn't even stimulate the tooth fillings next door to the transmitter.

Chris Campbell

[electra225]

Not only does this chassis have a tuned RF stage, but it also has two IF amplifiers. The model 1R81 chassis is almost like this one, except it has one less tube, one of the IF stages is omitted. IT is also a powerful performer. This chassis has no FM antenna and only a loopstick AM antenna. I hesitate tinkering with alignment on one of these chassis, as more harm than good can be done in the attempt to eke out a bit more performance. I'm really surprised that RCA provided a single-ended audio amp, since they over-built the front end. A 6V6 will provide 5 watts for the 8-inch speaker. These big RCA radio chassis work really nicely with the little RCA 45 player I have. There is four paper capacitors in the chassis that should be replaced. I may put a fuse in while I have the chassis out of the cabinet.