Motorola hybrid set 24ME Comet car radio
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Hi everyone,
I've just started working on this radio . It is an early 1960s set using 12 volt tubes and a two transistor output stage. Once I figured out which was the feed to the dial lights and which was the real power lead things went much more smoothly !
So now it goes though volume is low and a little distorted.My main concern is how the printed circuit board comes out and I'm hoping someone on the Phorum will have worked on this or a similar set.
It looks as though there is a bolt in the side which holds the board in but once this is removed it looks as though the board will only come out if the retaining bar is desoldered. Am I correct in this ?If anyone has any experience with this style of dis- assembly could they post a response here?
Thanks everyone and all the best.
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Good Morning! Can't say I've had experience with this one, but the schematic is in Beitmans volume 22.
Joe
Joe
Matthew 16:26 "For what does it profit a man if he gain the whole world, yet lose his own soul?"
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Hello Antipodal ,
first thing that would help is having the model number !
Sincerely Richard
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Hi,
You always find something interest to service! As Joe mentioned the service info is here on pg 51: https://www.worldradiohistory.com/Archiv...n-1962.pdf I haven't had direct experience with that model, but I have with the 12ME which is the 1960/61 version.
I have a parts chassis (12ME) because I needed a volume/tone/off-on switch. I would hazard a guess and say that the pcb is solder to the metal framework of the chassis. Which makes it a bit of a nuisance to remove. I'll take a look and see if I can find that chassis.
GL
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 10-24-2023, 09:48 AM by Radioroslyn.)
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When you de-solder anything on that PCB be careful with the heat. The PCBs of that era were made of a fibrous material that burns easily with high heat. Pretty much the same material as the wafer tube sockets.
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Hi fellows, The model number is Motorola 24ME. The Ford number is C2GY 18805-A . Thanks for your replies.
Yes, the board is not in the best condition - I notice that in some places the copper foil is lifting from the board and I 'm wondering what might be the best glue to stick it down again.Similarly I'm wondering which components I should look at first in the transistor audio section to track down the low output and distortion.In valve gear I would have greater confidence.
I do have the schematic which I got from Radiomuseum but thanks for the Beitmans reference -often there is more info there than in Radiomuseum. I will look that up.
But, yes, getting that board out is the priority.
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Printed circuit boards and tubes not my cup of tea!
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Hi Antipodal,
I had a 62 Comet (actually, it was a friend's father's car. Body not great, but he got it in 1974 for $40. I put a rear end and an engine in it and it became his car. Original engine ran but burned lots of oil and blew by, rings were gone. was either the 144 or 170 I6. Put a 65 200 I 6 in it, big improvement. Would have gone with a 66 but I think that the bolt pattern was different. These were rather good engines. Fuel starved due to the integral intake manifold and puny carb, but good engines. His wife did not drive and after he died, I used the car and drove the widow to the store, doctor, etc. till I got my own car. Friend's sister's boyfriend sold it for $500 in 1980. I hope someone restored it. Had the 2 speed slush-box. Was the S22 model, had the nicer seats, was an upscale version of the Ford Falcon. I liked the chrome spoked steering wheel. Now, if it was the 63 with the 260 V8...
I never did have to work on the radio however. Most radios of this vintage allowed rear access to the PCB by taking covers off.
I would try signal tracing techniques. However, first check out the radio to see if the thermistor shown in the schematic exists in your radio. If so, try bypassing it. I believe that the 2N176 is socketed but you have to carefully desolder the other transistor. Maybe the heater voltage for the detector /1st AF tube is too low, that would cause low sound and distortion. Also, check all resistors in the transistor section of the circuit. You may have to remove the transistors. The 2 Xistors are germanium, I think. You can pull the 1st audio tube and, using a cap, inject a signal from a cd or MP3 player. Don't expect the cleanest sound; germanium transistors were not quite "HiFi". Working the other way, put the tube back in, and use a cap to connect the plate of the 1st AF to the line input of a tube type amp (Phono input on a vintage radio will suffice. Good AM sound should result. If not, start swapping tubes. and checking caps, resistors, etc. These are "space charge" tubes and were only used in the 58 - 62 model years for Ford (and a lot of others). Funny, Lincoln and T-Bird had all Xistor in 1961, Lincoln had FM available in 1962. Rest of Ford and Merc went all Xistor in 63. A 63 Falcon radio would be a bolt in fit for your Comet, if the same as US models of that vintage.
Regarding the board, there should not be too much heat damage from the tubes, they don't really run that hot. Foil can be glued down with either cyanoacrylate glue (Krazy Glue or Gorilla Glue in the US), Duco cement or a non-metallic epoxy. If foil is bad use solid wire and glue down with any non-conductive glue.
Hope this helps.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
(This post was last modified: 10-25-2023, 12:27 AM by MrFixr55.)
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Hello everyone, Some progress has been made with this set but perhaps not with the musings which follow.
I mentioned , I think , that it does actually go - only with some distortion and the volume is down.Where is the distortion and low volume ? Which side of the volume control? Well, the probe on the Eico Signal Tracer placed on the top of the volume control delivers a big fat distortion free (relatively !) signal to the tracer speaker so I'm picking the problem lies with the transistor audio amp section.There be dragons for me!The power transistor is screwed to a cast metal section of the chassis (it gets remarkably warm -that part of the chassis acting as a heat sink )with two screws with a peculiar top - not Philips ,square or normal or any of the other "tamper proof" screw heads we get nowadays but with a screw I have read about in ads in "Radiocraft" whose chief merit seems to have been speed of assembly. The slot in the head is like a circle with two little opposite facing arcs cut out. No doubt someone will recall the trade name for these screws.
I do not have a screwdriver that fits this head,nor can I easily fabricate one. But I'm getting ahead of myself here. It may be that this transistor is fine and will not need removal.
So - back to getting the board out. The board sits in the chassis like a file in a filing cabinet drawer , the front of the " drawer " being the dial and push buttons. The board is located in four dimples in the bottom of the "drawer". At the top, as mentioned it is held in by a u-shaped bar , bolted on one side and soldered on the other . Bolt removed and iron and soldering wick applied and two tabs bent down and the bar which has held this board captive for 61 years is released.Does the board pop out ? No. The wires which connect the board to the other components are too short to allow the board to be lifted out.So a lot of cutting and tagging and pictures and notemaking will be required before the transistor section can be comfortably measured and assessed and hopefully repaired . It can be done but it will take time.
One gets the impression Mr Motorola might have got the actuaries in when designing this radio."Well,boys,how long will these 12 volt valves last in car radio service?Uh huh - that long eh? And the transistors?Not so sure but probably ...Hmmm. Okay, our pick then is the sets will outlast the car in normal service so there will be no servicing or warranty issues so yes, go ahead ,build the sets and it wont matter that the boards are barely seviceable."
Perhaps I've watched Madmen or Suits too much.
But here we are 61 years later wrestling with this set ,trying to get it to go properly , while surrounded by electronic devices of a capability and sophistication unimagined that long ago. Did bronze age men pick up stone age tools, re -sharpen them and run after woolly mammoths? And will the breakthrough for artificial intelligence have come when we discover a robot playing wistfully with a screwdriver inside a 1930s Zenith?
Time I went to bed!
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