Magnavox 70s console - Printable Version
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+--- Thread: Magnavox 70s console (/showthread.php?tid=19401)
RE: Magnavox 70s console - 462ron - 01-26-2019
Hmmm, that N750 is in parenthesis and I believe it refers to C9. None of the transistors on this print anywhere have a part number assigned to them on the print, only Q numbers. The number on the original transistor crosses to an ECG161 which is also stated in the parts list and is a Si part. I wonder if the discrepancies in the voltages could be because the osc isn't running? If it were, maybe they would be closer to the numbers on the print. I took readings on the RF amp and IF amp and they are in the ballpark like the osc but not exactly. Do you think they were using germanium xistors in the mid 70s? I understand germaniums are hard to come by! I don't know as I don't usually work on SS stuff. One quirk I noticed today was besides the local station, I could hear a second one in the background but again, tuning has no affect!
Ron
RE: Magnavox 70s console - morzh - 01-27-2019
It could be due to oscillation. It's just if transistor is conducting all the time (which I think common base does) the average DC reading of Vbe should be about 0.7V. If of course it is conducting.
I'll look on the simulation Monday.
RE: Magnavox 70s console - 462ron - 01-27-2019
Just for giggles, on Monday I'm going to see if I have a germanium xistor lying around and try it. Just in case the ECG161 is a misprint. I can't tell you enough how I appreciate all your input on this!
Ron
RE: Magnavox 70s console - morzh - 01-27-2019
Just make sure the Ge transistor you have is a Hi frequency device.
RE: Magnavox 70s console - Arran - 01-28-2019
I'm a bit rusty with S.S stuff, but I think you can tell a germanium verses a silicon transistor by the values of the bias resistors, if you don't have the number on hand. Incidentally, what do the packages look like on these transistors, if they are black, round, with a domed top they are silicon, made by Fairchild, which are not the most reliable ones ever made, probably worse then many germanium types. The habit in the late 1960s and early 70s was to use silicon in the front end, and the IF strip, but use germaniums in the audio output stages, there was an idea that they would more hi fi, my portable 8 track player has this.
Regards
Arran
RE: Magnavox 70s console - 462ron - 01-28-2019
Thanks Arran, yes I've come to the conclusion that most germanium units are power/ audio Amps. I checked my stash of xistors and the only Ge type I have is a PNP. Upon checking my Sylvania ECG replacement guide, there aren't many Ge type replacements, most being PNPs. The few NPNs I saw were mostly power amps and audio drivers save for one, an ECG101. That type looks to be an AM RF amp/ oscillator/ mixer. Not good for the FM band. So back to square one!
Ron
RE: Magnavox 70s console - morzh - 01-28-2019
Gosh, Ron,
what's with the fonts? Every letter takes half the screen
RE: Magnavox 70s console - 462ron - 01-28-2019
Sorry Mike, my iPad slows way down if I type directly on the forum to the point it almost stops. So, what I do is type my post on a notes app I have, then copy and paste it to the forum. It copies in a large font so I do a quick edit on the bottom and it returns the font to normal. Crazy I know!
Ron
RE: Magnavox 70s console - morzh - 01-28-2019
Oh yeah....all tablets slow down after some time. My Google has, my wife's iPad had to be retired and a new one bought......
RE: Magnavox 70s console - 462ron - 01-30-2019
After weeks and weeks of racking my brain and multiple testing and retesting of the FM section of this radio, I feel it's time to throw in the towel unless anyone has a last ditch effort I could try. It defies all logic but just can't find any reason for the oscillator to not oscillate! I thank Mike and others for all your help and time!
Ron
RE: Magnavox 70s console - morzh - 01-30-2019
Ron
If you could detach the PCB that has the oscillator on it so it can be easily connected to 11.3V, and send itto me, I could try to look into it some more.
RE: Magnavox 70s console - 462ron - 01-30-2019
After weeks and weeks of racking my brain and multiple testing and retesting of the FM section of this radio, I feel it's time to throw in the towel unless anyone has a last ditch effort I could try. It defies all logic but just can't find any reason for the oscillator to not oscillate! I thank Mike and others for all your help and time!
Ron
RE: Magnavox 70s console - morzh - 01-31-2019
De ja vu..
RE: Magnavox 70s console - 462ron - 01-31-2019
Thanks Mike but the whole radio, power supply and audio amp is one big board. The power switch, including sections for switching the record changer has a ton of wires and is separate from the pcb as is the power transformer. At this point, I would fear taking a chance shipping the whole chassis and front face and dial. I talked with the owner tonight and was told the radio was never great and that she mainly uses the record player and I got the amp working. I told her I would keep it a little longer in hopes of cracking this nut! I thank you for your offer.
Ron
RE: Magnavox 70s console - Ron Ramirez - 01-31-2019
Just a suggestion...
I see that 462ron is about 3-1/2 hours away from Mike.
Ron, have you considered driving to Jackson, NJ and taking Mike up on his offer?