Ron Joiner
New Member
http://www.ebay.ca/itm/DYNACO-FM-5-...EPLACEMENTS-/281910280204?hash=item41a329800c
Found this on EBay. The solution?
Found this on EBay. The solution?
Dynaco FM-5 indicator lights
- Thread starter NealinNevada
- Start date
They might be ok, but they look like just white LEDs without any bias resistors. If that is the case, they might not present the proper load to the tuner. The discussion above addresses this.
Ron Joiner
New Member
Hmmm. interseting
I got to try the MCM lamp, see http://www.mcmelectronics.com/product/25-505 or http://www.newark.com/mcm/25-505/la...ll+Categories&categoryNameResp=All+Categories. It appears to be correct--2chanman said that they are 12 V and 33 mA, the MCM bulbs are specked at 12 V and 35 mA, which should be close enough. It comes on when tuned, ges off when not tuned, and operate the muting circuit properly. It has a smaller diameter than the originals, so I just built up the ends of the wires closest to the bulb with some teflon tape until they had a snug fit. For the record, the bulb in circuit has 11.7 V drop across it when tuned/on, and 0.13 V across it between stations/off. This may vary some from tuner to tuner, but it is close to spec of the bulb.
Before I found the bulbs, I bought a 5 mm Radio Shack 276-0320 white LED that is rated at 20 mA at 3.2 V. I made a circuit using two resistors, one in parallel, called Rp in the attached sketch, the other in series called Rs. I didn't change any resistor on the board, I just soldered these together neatly and covered bare leads with shrink tubing.
The reasoning for two resistors goes like this: The bulb has 35 mA, while the LED should have 20 mA, so the parallel resistor should carry the difference of 15 mA. The bulb has 12 V across it, but the LED should have only 3.2 V, so the series resistor is needed to drop the voltage. There's a way to calculate this if you no the circuit source voltage, but it takes a little time. The closest standard resistor values are Rp=150 ohm, and Rs=220 ohm, as marked on the attached diagram.
As a check, I measured the voltage across the whole circuit, as I had done for the replacement bulb, and got 11.5 V when on, 0.23 V when off. Again, pretty close.
The LED is considerably brighter than the incandescent, so if you replace the tuned bulb with an LED, you'd probably want to replace the stereo bulb, too. I haven't calculated the circuit for this. It is probably the same, but it might be a bit different.
I hope this helps, and I hope that some of the other circuit people check my numbers, I'm not perfect.
Before I found the bulbs, I bought a 5 mm Radio Shack 276-0320 white LED that is rated at 20 mA at 3.2 V. I made a circuit using two resistors, one in parallel, called Rp in the attached sketch, the other in series called Rs. I didn't change any resistor on the board, I just soldered these together neatly and covered bare leads with shrink tubing.
The reasoning for two resistors goes like this: The bulb has 35 mA, while the LED should have 20 mA, so the parallel resistor should carry the difference of 15 mA. The bulb has 12 V across it, but the LED should have only 3.2 V, so the series resistor is needed to drop the voltage. There's a way to calculate this if you no the circuit source voltage, but it takes a little time. The closest standard resistor values are Rp=150 ohm, and Rs=220 ohm, as marked on the attached diagram.
As a check, I measured the voltage across the whole circuit, as I had done for the replacement bulb, and got 11.5 V when on, 0.23 V when off. Again, pretty close.
The LED is considerably brighter than the incandescent, so if you replace the tuned bulb with an LED, you'd probably want to replace the stereo bulb, too. I haven't calculated the circuit for this. It is probably the same, but it might be a bit different.
I hope this helps, and I hope that some of the other circuit people check my numbers, I'm not perfect.
Ron,
I just posted a reply on the thread. Sort answer is that the MCM bulb appears to be correct.
Ron Joiner
New Member
Thanks Capital C. Helps a lot and shows that it can be done with LEDs. Significantly cheaper than the ones I saw on EBay. Just sent an order to MCM Electronics
Ron
Ron
Last edited:
Ron Joiner
New Member
Had a chance to install the MCM bulbs and they work perfectly. In addition the mute circuit is now working correctly. By installing towards the rear of the bulb housing the lights are approximately the same brightness as before. I wound electrical tape until I got the right friction fit. thanks Capital C.
Ron
Ron
This is just the problem I was having with my FM-5. Thanks for the info! I could not load the link to mcm but the newark link is still valid. I have not installed the lamps yet. When i ordered the lamp in the link another lamp was suggested by the site. The lamp in the link is 2.4 mm in diameter and the suggested was 5.0 mm. I ordered both since it was stated that the lamps needed to be wrapped in order to make them fit. Maybe the 5mm will fit better. I'll let you know.
I appreciate the solution from Newark (MCM) and the previous related posts for an incandescent solution. However, these lamps/cables are only 200mm long--too short to make it to PC26. Not even close. I bought two pairs just in case and plan to do some splicing. The Newark link is still good, but I would buy the 5mm for better fit and bigger bulb.
