- Thread starter
- #21
Use this at your own risk. I'm just sharing information.
Not a schematic, but it could save a radio some day. The 08600-00014 radio used in 1970s FJ40s has a design issue that gets worse with age.
There are two output transistors mounted to the bottom right rear of the radio case. These transistors have bias diodes in plastic holders attached to them.
These diodes drift over time and the transistors will overheat and melt the diode holders. If you get one of these radios, monitor that part of the case when first powered up, if it gets hot power it down, you need new diodes and hopefully you have not melted the diode holders.
If you do need diodes, they were originally KB-162 and were commonly used in amps in the 70s. Sadly these are like hens teeth now and everyone refurbing their vintage amps want them too. I found a couple resources for these. I have some KB-165 diodes which have almost the same I-V curve as the KB-162. There were a few versions (KB-162, KB-162C4, KB-162C5B) I assume are variants with different power or current ratings. The KB-165 diodes work. I think I have the last new ones on the planet. I have seen 1N4148, BA216 and BA-314, NE601 specified as a replacement for the KB-162 but these need to have the same mV/C and Vf ratings when used for temperature compensation. I have not tried these replacements.
If you have melted down diode holders, all is not lost. The CHV91 radio used in the Chevy luv has the same diode holders. I have picked up a few for cheap over the years so I can help you with those too.
And finally, I found the service manual for the Phillips AN279 radio that has a similar output stage. They specify a BZX79C5V1 diode which is a currently available part new, made by onsemi. I have not tried using these diodes.
Not a schematic, but it could save a radio some day. The 08600-00014 radio used in 1970s FJ40s has a design issue that gets worse with age.
There are two output transistors mounted to the bottom right rear of the radio case. These transistors have bias diodes in plastic holders attached to them.
These diodes drift over time and the transistors will overheat and melt the diode holders. If you get one of these radios, monitor that part of the case when first powered up, if it gets hot power it down, you need new diodes and hopefully you have not melted the diode holders.
If you do need diodes, they were originally KB-162 and were commonly used in amps in the 70s. Sadly these are like hens teeth now and everyone refurbing their vintage amps want them too. I found a couple resources for these. I have some KB-165 diodes which have almost the same I-V curve as the KB-162. There were a few versions (KB-162, KB-162C4, KB-162C5B) I assume are variants with different power or current ratings. The KB-165 diodes work. I think I have the last new ones on the planet. I have seen 1N4148, BA216 and BA-314, NE601 specified as a replacement for the KB-162 but these need to have the same mV/C and Vf ratings when used for temperature compensation. I have not tried these replacements.
If you have melted down diode holders, all is not lost. The CHV91 radio used in the Chevy luv has the same diode holders. I have picked up a few for cheap over the years so I can help you with those too.
And finally, I found the service manual for the Phillips AN279 radio that has a similar output stage. They specify a BZX79C5V1 diode which is a currently available part new, made by onsemi. I have not tried using these diodes.
Last edited:
