I have an RCA 632-11. All fm stations were working before and after the recap. I believe they quit after mounting the tuner back into the console. Now with AM the stations are controlled by a tuning capacitor, but with FM it uses a multiplexer right? Would that be the 6ba6 tube?
Is there anything else I could double check? I start to lose stations after 95, and there is nothing. No static when sweeping or anything!
Is there anything else I could double check? I start to lose stations after 95, and there is nothing. No static when sweeping or anything!
Yeah I reconnected the antenna. I'm going to try swapping the 6ba6 tubes around and see if the problem reverses itself and I lose the bottom stations. If that doesn't work I'll remove it and take a look!
Sorry for the double post. Looks like I didn't replace C34 or C44. Not sure how I missed those but it appears C34 runs to L9 which is the 1st AM IF and then it runs to L6 which is the 2nd FM IF.
AM works fine so that signal path might not be right, bit it's hard to do any guesswork while there is still caps that need replaced
I did screw down that strip and didn't leave it loose in there. You can see the 2 caps I didn't replace on the bottom
AM works fine so that signal path might not be right, bit it's hard to do any guesswork while there is still caps that need replaced
I did screw down that strip and didn't leave it loose in there. You can see the 2 caps I didn't replace on the bottom
Of course, changing 6BA6 FM IF amplifiers alters alignment. 🙁
Do you have the sophisticated test bench needed to perform a proper FM sweep alignment? If not, take the unit to a reliable technician who has the appropriate equipment.
Do you have the sophisticated test bench needed to perform a proper FM sweep alignment? If not, take the unit to a reliable technician who has the appropriate equipment.
Honest question, would replacing capacitors take out exactly one half of the FM transmission? I'm not doubting you, just trying to understand.
And no, I only have enough equipment to be dangerous. I'm building towards a proper bench, but all in due time. I'm fairly new to all of this
Tubed radio circuits are finicky buggers. Replace a tube or a key passive part and alignment goes out. The sound of a transformer coupled IF strip remains the "Gold Standard". They have been used with SS, but ceramic filters are the norm for those devices.
Radio from "simple" AM up to RADAR is quite different than audio. Many years ago, Hugo Gernsback remarked about how many a good radioman had trouble with speech (audio) amplifiers. The other way around is equally true.
Radio from "simple" AM up to RADAR is quite different than audio. Many years ago, Hugo Gernsback remarked about how many a good radioman had trouble with speech (audio) amplifiers. The other way around is equally true.
Whoa baby!
Ya got yourself a real ballbuster there in that chassis!
Unless you've got ALL the right equipment, documents, and all the proper training in how to use them, you're in for a mess of trouble.
Those RCA Victor tube chassis are not fun to fiddle with.
Trust me, I own an RCA console from 1963 with a similar tuner chassis (RC-1205C), and even WITH all my decades of being a service professional, it took all of my wit and patience to overhaul that thing.
AND, I'm "RCA certified" as well.
Going into that chassis and attempting to perform a "recap" is dangerous - so many mistakes can be made, because RCA deliberately designed them to strict assembly standards.
If even a wire is moved slightly out of position, it'll throw off alignment.
My RCA service manuals confirm that!
All I'm gonna say is - you opened up a can of worms now.
Some guy sent me a chassis like that halfway across the country because "it wasn't right after their tech messed with it"
Good luck. 😱
Ya got yourself a real ballbuster there in that chassis!
Unless you've got ALL the right equipment, documents, and all the proper training in how to use them, you're in for a mess of trouble.
Those RCA Victor tube chassis are not fun to fiddle with.
Trust me, I own an RCA console from 1963 with a similar tuner chassis (RC-1205C), and even WITH all my decades of being a service professional, it took all of my wit and patience to overhaul that thing.
AND, I'm "RCA certified" as well.
Going into that chassis and attempting to perform a "recap" is dangerous - so many mistakes can be made, because RCA deliberately designed them to strict assembly standards.
If even a wire is moved slightly out of position, it'll throw off alignment.
My RCA service manuals confirm that!
All I'm gonna say is - you opened up a can of worms now.
Some guy sent me a chassis like that halfway across the country because "it wasn't right after their tech messed with it"
Good luck. 😱
It looks like it uses 1/2 of the 6DT8 as a combination local oscillator / mixer for FM.
I would suspect the FM band local oscillator is dying about halfway through the tuning range.
It's generally best to leave tuned circuits alone, if they're working properly. If the capacitors that you changed were in the tuned circuits, it could be problematic to re align them without some type of signal generator. Orange drops may or may not have been a good replacement capacitor - it depends on the circuit function.
I would suspect the FM band local oscillator is dying about halfway through the tuning range.
It's generally best to leave tuned circuits alone, if they're working properly. If the capacitors that you changed were in the tuned circuits, it could be problematic to re align them without some type of signal generator. Orange drops may or may not have been a good replacement capacitor - it depends on the circuit function.
wiseoldtech said:
That's a joke, right? That thing was thrown together as fast and cheap as possible.
Wrong.
You obviously don't have any RCA Victor service manuals on tube tuners in your library.
It's mentioned in their manuals under "critical lead dress".
I found out the hard way when servicing mine, but believe whatever year heart desires.
Thanks for the solid info! I may still have the original caps, I'll look and think about swapping. The good news is this thing sounds beautifully with the rca inputs I added. Surprisingly, considering the fact that I'm far from being rca certified
I would look for a bent plate in the variable tuning capacitor. It shorts out when the capacitor is turned to a specific spot and stops anything working past that. So with power long off measure the DC resistance of each section across the range of motion. Usually you can see the problem without any tools.
Try replacing the 6DT8.
If it doesn't help, you can allways use that tube, it's also a nice AF one.
Mona
If it doesn't help, you can allways use that tube, it's also a nice AF one.
Mona
The tube sockets can also be troublesome and/or bad. Try wiggling the 6DT8 (and others) in their sockets and see what happens.
I see two adjustable coils that look like they’ve had their resonator caps changed out. Judging by the size, I’d venture a guess that they are in the FM MPX circuit (19 and 38 kHz).
One is just adjusted for maximum suppression of the 19 kHz pilot tone the other to peak the gain at 38. But you do have to know which is which to scope it, and FAR easier with a modulated signal generator than with just receiving a strong station. It’s hard to pick out the pilot tone if it’s buried in audio. This does not affect mono operation. You also appear to have a couple red power supply wires running thru there which probably shouldn’t. Stray coupling like that is part of the “critical lead dress” that was referred to. And I could be entirely wrong as to their function. The FM IF strip ( and many times AM) transformers are in the little cans that stick out the top. Never mess with those unless you KNOW there is a fault. Retuning is possible if you had to, but not by ear on FM unless you’re ok with poor distortion performance (requires staggered tuning to be optimum). The good news on those is the resonating caps are inside the cans where you can’t get to them. If the transformer goes out (almost never unless you break it) you replace the whole thing.
None of the other replaced caps look like they are in any critical tuned circuit. The bent air cap plate theory does fit observations and start there regardless. There are several ganged sections that need to track each other, and could be any one of them.
One is just adjusted for maximum suppression of the 19 kHz pilot tone the other to peak the gain at 38. But you do have to know which is which to scope it, and FAR easier with a modulated signal generator than with just receiving a strong station. It’s hard to pick out the pilot tone if it’s buried in audio. This does not affect mono operation. You also appear to have a couple red power supply wires running thru there which probably shouldn’t. Stray coupling like that is part of the “critical lead dress” that was referred to. And I could be entirely wrong as to their function. The FM IF strip ( and many times AM) transformers are in the little cans that stick out the top. Never mess with those unless you KNOW there is a fault. Retuning is possible if you had to, but not by ear on FM unless you’re ok with poor distortion performance (requires staggered tuning to be optimum). The good news on those is the resonating caps are inside the cans where you can’t get to them. If the transformer goes out (almost never unless you break it) you replace the whole thing.
None of the other replaced caps look like they are in any critical tuned circuit. The bent air cap plate theory does fit observations and start there regardless. There are several ganged sections that need to track each other, and could be any one of them.
Are you sure you have the correct circuit diagram?
Your diagram shows the FM RF amp and mixer oscillator in a separate compartment, with a variable inductor for the tuning.
It then goes to the first IF amp through a connection on the chassis, a shielded cable, and then to the first IF amp grid. Maybe I am not looking hard enough, but I don't see any of this.
Your diagram shows the FM RF amp and mixer oscillator in a separate compartment, with a variable inductor for the tuning.
It then goes to the first IF amp through a connection on the chassis, a shielded cable, and then to the first IF amp grid. Maybe I am not looking hard enough, but I don't see any of this.
The "multiplexer" is part of the circuit that recovers stereo from the FM broadcast. it can not cause this issue. The part of the radio that tunes the FM band is associated with the 6DT8 tube. The pictures do not show it, but the schematic implies that the FM is tuned by moving a pair of slugs up and down inside coils. Messing with this stuff is NOT a good idea.
The statements about not messing with anything in the RF sections are good. The oscillator rune at a frequency above 100 MHz. That was pretty high frequency back then.
You say that it all worked before reassembly, but cuts out now. Does "No static" mean the the background hiss disappears above 95 on the dial? If so I would suspect something (a wire maybe) is getting caught or otherwise shorted out when the pulley on the tuning cap rotates. Trouble in the 6DT8 circuit would kill the stations, but not the FM hiss.
The 6DT8 and its components were often mounted in a separate can on top of the chassis.
I thought that was just for AM? When I turn the FM dial that tuning cap doesn't turn at all.