Re: Larry's 1951 Club Sedan Project
Posted by Larry51 On 2011/12/26 7:07:07
Restoration of '51 Radio(s)
While the weather stopped other work on the car I decided to get the two '51 radios (Model 416387) I have out and see if I could get them working. I had the circuit diagram, handbook and one full set of original valves just in case, but I was soon to discover that I need not have ordered all the valves!
Long ago I replaced all the capacitors in both units but didn't get any further, putting the radios back into storage for a couple of years, until now. I didn't have a power supply then or a decent 6V battery to use for testing. Both radios are in fair condition mechanically and electrically. They haven't been 'left out in the rain' or stored in poor conditions.
Some caps are old micas with a strange colour code. These are Cornell-Dubilier caps and I managed to get a copy of the colour code which is available at
Cornell-Dubilier Code
It takes a bit of figuring out, as the code differs from the general colour codes for resistors and caps etc. Usually mica caps will be ok, they don't deteriorate like waxed paper caps. First step is to always replace any old wax/paper caps when doing up an old radio.
I unplugged a vibrator can from one chassis and applied 6volts to it - no action. Decided to see if I could repair it. My brother (who was in the radio and TV repair business for many years) reckoned most could be repaired provided you took care opening the sealed can. I carefully ground the rim off the can and pulled the unit out. Both sets of contacts were shorted with metal filings and gunk. They cleaned up well when I dragged some fine emery paper between them. You should see an air gap between both sets of contacts. No adjustment was needed.
The radios had not been used since at least 1975, and probably long before then, so I had little confidence that either would work straight up, but I was to get a surprise. At around 4 volts from the supply the vibrator started. I measured a few voltages but there was no HT. Turned the volts up to over 5V and I got static and finally a station. I had decent B+ voltage! The fidelity was really poor as the speaker was old and in poor condition. In fact it might have been original, around 60 years old.
Tuning pulled in other stations but occasionally the OZ4 rectifier valve would just quit. There's an intermittent connection or a marginal valve elsewhere which I need to eventually find.
Left the radio on for over an hour and it continued working well. Hooked up a new 6 x 9 speaker and the fidelity was much better - even OK to listen to.
Next I powered up the second set, and the vibrator worked OK but there was no high tension (B+) voltage. Looks like there is an open circuit in the vibrator transformer winding, so I'll have to find a replacement. These are rare so it might take a while.
I might not have time to work on the second radio for a while, with holiday visits etc happening.
775 &776: views of the vibtator can and innards. The unit can be opened by grinding off the retaining lip around the bottom.
776?: The vibrator after the contacts had been cleaned. Air gap is now visible between contacts.
782: Vibrator case showing lip ground away
779: The power supply. Very handy as you can bring voltage slowly up to reduce the chance of damage, while looking for 'smoke and fire'!
800: The Rectifier tube (OZ4) glowing nicely. It can be easily replaced with a solid state unit for extra reliability, but OZ 4 valves are only a few bucks each anyway and keep things 'original'.
762: One of the radios showing the replacement capacitors and the unusual Dubilier mica caps.
724: A 'ring-in' miniature valve has been substituted in the past . . . it works aok
757: Getting a replacement speaker is proving to be difficult. They are low profile and a tight fit in the chassis.
While the weather stopped other work on the car I decided to get the two '51 radios (Model 416387) I have out and see if I could get them working. I had the circuit diagram, handbook and one full set of original valves just in case, but I was soon to discover that I need not have ordered all the valves!
Long ago I replaced all the capacitors in both units but didn't get any further, putting the radios back into storage for a couple of years, until now. I didn't have a power supply then or a decent 6V battery to use for testing. Both radios are in fair condition mechanically and electrically. They haven't been 'left out in the rain' or stored in poor conditions.
Some caps are old micas with a strange colour code. These are Cornell-Dubilier caps and I managed to get a copy of the colour code which is available at
Cornell-Dubilier Code
It takes a bit of figuring out, as the code differs from the general colour codes for resistors and caps etc. Usually mica caps will be ok, they don't deteriorate like waxed paper caps. First step is to always replace any old wax/paper caps when doing up an old radio.
I unplugged a vibrator can from one chassis and applied 6volts to it - no action. Decided to see if I could repair it. My brother (who was in the radio and TV repair business for many years) reckoned most could be repaired provided you took care opening the sealed can. I carefully ground the rim off the can and pulled the unit out. Both sets of contacts were shorted with metal filings and gunk. They cleaned up well when I dragged some fine emery paper between them. You should see an air gap between both sets of contacts. No adjustment was needed.
The radios had not been used since at least 1975, and probably long before then, so I had little confidence that either would work straight up, but I was to get a surprise. At around 4 volts from the supply the vibrator started. I measured a few voltages but there was no HT. Turned the volts up to over 5V and I got static and finally a station. I had decent B+ voltage! The fidelity was really poor as the speaker was old and in poor condition. In fact it might have been original, around 60 years old.
Tuning pulled in other stations but occasionally the OZ4 rectifier valve would just quit. There's an intermittent connection or a marginal valve elsewhere which I need to eventually find.
Left the radio on for over an hour and it continued working well. Hooked up a new 6 x 9 speaker and the fidelity was much better - even OK to listen to.
Next I powered up the second set, and the vibrator worked OK but there was no high tension (B+) voltage. Looks like there is an open circuit in the vibrator transformer winding, so I'll have to find a replacement. These are rare so it might take a while.
I might not have time to work on the second radio for a while, with holiday visits etc happening.
775 &776: views of the vibtator can and innards. The unit can be opened by grinding off the retaining lip around the bottom.
776?: The vibrator after the contacts had been cleaned. Air gap is now visible between contacts.
782: Vibrator case showing lip ground away
779: The power supply. Very handy as you can bring voltage slowly up to reduce the chance of damage, while looking for 'smoke and fire'!
800: The Rectifier tube (OZ4) glowing nicely. It can be easily replaced with a solid state unit for extra reliability, but OZ 4 valves are only a few bucks each anyway and keep things 'original'.
762: One of the radios showing the replacement capacitors and the unusual Dubilier mica caps.
724: A 'ring-in' miniature valve has been substituted in the past . . . it works aok
757: Getting a replacement speaker is proving to be difficult. They are low profile and a tight fit in the chassis.
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