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Midland 13-898B Low SSB Power Out
- Thread starter Justin B.
- Start date
I think that resistor is ok if you have 13v there.
I just don't understand what could be pulling the audio down to 320mV pk-pk with almost 3vpk-pk on the other side of that cap (C309). Something must be pulling it down. With the radio off, what resistance do you have between the cathode of C309 and ground? It may take a few seconds for the reading to settle as the meter charges the caps.
Schematic suggests 8.3k
I just don't understand what could be pulling the audio down to 320mV pk-pk with almost 3vpk-pk on the other side of that cap (C309). Something must be pulling it down. With the radio off, what resistance do you have between the cathode of C309 and ground? It may take a few seconds for the reading to settle as the meter charges the caps.
Schematic suggests 8.3k
Brandon - I measured 7.91K so I reckon that's close enough for government work!
edit: see next post
You have waveforms showing 2.74v pk-pk at pin 6 and only 320mV pk-pk at the cathode of C309. The ohms look right on that side of the cap, so IMO, it can only be a couple things. 1, C309 is dry, but you said you changed all caps, so I doubt it. 2, those diodes are conducting well below 0.7v, but everything I find online suggests silicon, so that doesn't seem right either. 3, maybe the 320mV pk-pk is a false reading taken during a low in your voice and I am focused on the wrong area ~ one of the reasons to inject a constant tone when looking at signal levels.
I would start with eliminating the mic and injecting a steady 1kHz tone at 30mV pk-pk and get new waveform screenshots around those same points.
I have this modeled in LTSpice and can share the file when I get home if you want to mess with it. My model shows roughly the same pk-pk on pin 6 and the other side of C309.
I have a radio with a similar circuit, a midland 13-892, but I need to recap and align it before I can use it as a waveform reference. Not sure I will have time to go through it this week.
I would start with eliminating the mic and injecting a steady 1kHz tone at 30mV pk-pk and get new waveform screenshots around those same points.
I have this modeled in LTSpice and can share the file when I get home if you want to mess with it. My model shows roughly the same pk-pk on pin 6 and the other side of C309.
I have a radio with a similar circuit, a midland 13-892, but I need to recap and align it before I can use it as a waveform reference. Not sure I will have time to go through it this week.
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hey, wait a minute.... I think I have interpreted this wrong
It says 320mV pk-pk, but in the yellow box, that suggests 2v per division (I missed that). So its almost 3v pk-pk on that side of the cap too. Ok, cool!!!! Worn out pot wipers???
Rigol makes a good scope, not dissin' it, but I feel like their interface designers came from the automotive side of the trade.
Sorry for dragging you along thinking there was an issue. Many of the other waveforms were at 500mV/div and I didn't even question it. Just figured the 320mV was the max. My bad.
It says 320mV pk-pk, but in the yellow box, that suggests 2v per division (I missed that). So its almost 3v pk-pk on that side of the cap too. Ok, cool!!!! Worn out pot wipers???
Rigol makes a good scope, not dissin' it, but I feel like their interface designers came from the automotive side of the trade.
Sorry for dragging you along thinking there was an issue. Many of the other waveforms were at 500mV/div and I didn't even question it. Just figured the 320mV was the max. My bad.
Brandon - Not a problem and I really appreciate you taking time to help me with this.
Not sure why I changed settings on that one but it must have made sense to me at the time!
This is going to have to go up on the shelf for a few weeks as I'm fixin' to head out to our off-grid cabin in OK. Maybe I'll come back with a clear head and the problem will be staring me in the face!
73,
Not sure why I changed settings on that one but it must have made sense to me at the time!
This is going to have to go up on the shelf for a few weeks as I'm fixin' to head out to our off-grid cabin in OK. Maybe I'll come back with a clear head and the problem will be staring me in the face!
73,