Overhauling the radio

[1949plymouthdeluxe]

Thought I would stick this on here but over the weekend I overhauled the radio in the plymouth. I work on a lot of old radios but not many car radios. The wires had been snipped and when I first tested with a power supply nothing happened. Tube filaments and pilot lights came on but no B+. The radio uses conventional AC tubes you'd find in many AA5 table sets. It does have push-pull audio and uses a pair of 6AQ5 tubes, which are nearly the same as a 6V6 octal tube. 

 These use a "vibrator" which mechanically converts 6 volts to AC which then is used by a transformer to create the high voltages needed for the tube plates. Anyway, it is absolutely key to COMPLETELY replace all of the capacitors in these. Not only do the old caps suffer from being in a hot car for decades but the vibrator beats the crap out of a 1600 volt "buffer" cap that goes from the vibrator to the transformer. Its key to meet or exceed that voltage. 

 Took around 5 hours to recap. The space is very tight compared to the sets I usually work. And its important to keep the caps as close to their original locations. I used 104 degree rated electrolytics.  I replaced all caps except a few that were difficult to reach. The first test resulted in very poor audio and reception. Turned out the last cap that was the most difficult to reach was shorted. That and the 6BA6 tube it was associated with was very weak. As I volunteer at a local museum that has at least 50,000 spare tubes I got a fresh set of output tubes, a new rectifier and new tubes to replace those that tested less than perfect. On table sets I'll leave even semi-weak tubes in since those are easy to change. Not as easy to get the car radio out so its going to have all good tubes. I might install LED pilot lights. Not sure.

 I also added an audio cable that comes off of the volume control. right and left channels are tied through a set of 30ohm resistors to get true mono. Tied resistors goes to the pos of the volume control. Neg goes to ground. This way I can either listen to the radio, which is AM only or listen to a bluetooth module that plugs into a audio cable that can run into the glove box.

 Good thing I fixed my charging problem. The set uses a whopping 8 Amps meaning it wouldn't take long to drain the battery with the radio alone.

[Veemoney]

looks similar to this unit been sitting on the shelf for about 18years. never gave it a try. Someone took the time to install it in a wood box with carry handle. I picked it up at a swap. Glad to see folks still getting these up and running. 

[sidevalvepete]

Good post. Thanks for sharing your knowledge and detail...

[Young Ed]

1 hour ago, Veemoney said:

looks similar to this unit been sitting on the shelf for about 18years. never gave it a try. Someone took the time to install it in a wood box with carry handle. I picked it up at a swap. Glad to see folks still getting these up and running. 

That's dangerous. Dad bought a 50 Plymouth radio at a swap I think in 89-90. Ran into someone in the parking lot that said oh you must have a 50 Plymouth. Dad says no and they get to talking and a few weeks later that guys car became Dad's. 

[65bcoda]

Looking at your photo with the top off..........has me scratching my head........LOL

[Oldguy48]

Thank you for an excellent post!  

[1949plymouthdeluxe]

Really not that complicated. If you can work on a car you can fix these radios. The most important thing is to replace all of the old capacitors. All of the bright yellow and brown things are new above. Most have their values and voltages. So even if you can't read a schematic just replace the same with same. In mine the caps are all called " Bumblebee" caps and have colored bands that are read in order like a resistor. There were many that had yellow, violet and orange bands. That reads as 4,7, and three 0's so 47,000 picofarads or .047 microfarads. They sell the new caps cheap as in a few cents per cap, a little more for the electrolytic ones. 

[D35 Torpedo]

35 minutes ago, 1949plymouthdeluxe said:

Really not that complicated. If you can work on a car you can fix these radios. The most important thing is to replace all of the old capacitors. All of the bright yellow and brown things are new above. Most have their values and voltages. So even if you can't read a schematic just replace the same with same. In mine the caps are all called " Bumblebee" caps and have colored bands that are read in order like a resistor. There were many that had yellow, violet and orange bands. That reads as 4,7, and three 0's so 47,000 picofarads or .047 microfarads. They sell the new caps cheap as in a few cents per cap, a little more for the electrolytic ones. 

I wanted to tackle my radio but i didnt recognize the caps, this makes sense. I have the same radio as yours, 805 if i remember correctly. Ive read that people will open up the vibrator to clean and file the points, is this necessary? Can you show my how you wired the aux cord? I found a replacement radio that was removed from a car in the 60s as my original was pretty ugly inside, someone was in it before me. Thanks for posting your knowledge, gives me confidence as i am not experienced with radios and don't want to pop mine.

[1949plymouthdeluxe]

Here is a great place to start:
https://antiqueradio.org/recap.htm

 There are TWO very different capacitors in this radio. A aluminum can mounted up top that has 4 capacitors inside. The values and voltages are marked on the side of the can and has symbols to indicate what lug underneath is what. It is VERY important that these are wired in the right polarity. Chassis is negative and the leads that go to each lug of the can are positives. If you look at the images and see the new brown caps, those replaces the 4 values of the aluminum can.  The rest of the caps are NOT polarized and can go in either way. The most important cap goes to the transformer inside a metal shielded box. Remove the top and you'll see it. Its something like a .003 Microfarad cap at 1600 volts DC. That thing gets beat to death.

 Here is a link to decoding the bumblebee caps:
https://pickguardian.com/wp-content/uploads/2014/04/Sprague-Bumblebee-Chart.pdf

As far as aux cord to the radio the set has a dual stacked pot, which is the volume and tone control. Each of those will have three leads: A top, bottom, and a center lead. Ignore the center lead. These come right off the volume control itself ( the thing that the volume knob is attached to ) I ran a 3.5mm stereo cable into the set with a 3.5 mm male at the end. Take the right and left channels and run each side to a 30 ohm, 1/4 watt resistor. Then tie the two resistor leads the other end together. That will mix R an L channels together safely. Then that will go to the positive side of the volume control. Its the side where the radio signal comes in. You can test with some clip leads first.

 I'll try and post better pics later. 

[docrock]

Wow. Very cool info. Thank you

[1949plymouthdeluxe]

Yesterday I re-assembled the radio. I had previously let it sit and run on the power supply on the bench for a few hours. I'd rather something go wrong on the bench than installed in the car. I used some strips of rubber mastik tape to insulate the speaker and the radio from the chassis as well as the dash for preventing the speaker from causing nasty vibrating sounds. The switch for the radio is broken. Its a wafer switch stamped to the push button board assembly. No way to get that off without more disassembly. So I installed a switch under the dash. 

 It works pretty well. Too bad its just AM radio. Very sensitive. Bluetooth works and I need to find a place to stick it where its out of sight. For what it is it does actually sound pretty good. 

[Booger]

Nice work. I regret not putting a bluetooth option when I had mine rebuilt. But at least we have a decent oldies station around here

[Ivan_B]

No need to mess with the vibrator if it is still vibrating. If you have not been using resistor spark plugs or wires, you will now

If you want to listen to the authentic AM, just install a transmitter with an MP3 player.

Edited October 2 by Ivan_B