04-09-2014, 03:23 PM
That makes sense. The 170 uses an IC for MPX decoding, even though it used a "grain of wheat" 8 volt lamp for the Stereo Beacon. The LED replacement worked perfectly in the 170; you could not ask for a better conversion. Now, the 4400 uses an older MPX board than that used in the 700. My 440-T uses the same type of MPX board as the 4400, although there is a 440 on eBay now that uses the same MPX board and, it appears, the same driver boards as the 700. But I digress. I'll try to find a 15V bulb that is at, or close to, 30 mA and will try it. I took a quick look on Mouser's site on my lunch break but did not see any 15V lamps - only 14V and 18V, and neither of those were rated at 30 mA filament current.
I just realized something, looking at the 700-T schematic - voltage at the junction of R46, R47 and C17 is 25V in mono, 17V in stereo. Looks like the ideal lamp is 17V?
[Video: http://youtu.be/29BoqCMRBFk]
In the meantime, I will still pull those two transistors in a little while and report back on my findings.
I just realized something, looking at the 700-T schematic - voltage at the junction of R46, R47 and C17 is 25V in mono, 17V in stereo. Looks like the ideal lamp is 17V?
[Video: http://youtu.be/29BoqCMRBFk]
In the meantime, I will still pull those two transistors in a little while and report back on my findings.
--
Ron Ramirez
Ferdinand IN
