ok, after reading through this thread, i have to tell you CBphreaker that this is the best thread i've run across in a long time.
so much to discuss!
To start with, on the low distortion AM detector circuit (the coolest part of this to me), i'm not seeing where any test equipment is necessary.
from the description given in the link, it sounds like you just lift a component lead to disable the AGC (not sure which one yet, as i haven't looked at a 148GTL schematic yet to find it)
Then tune the pot on the detector board by ear and using the radio's S-meter.
from the way he describes it, there should be a definite "sweet spot" with that pot and should be attainable by ear.
Please let me know if i am mistaken about this.
I would think that a TL082 could be used here, as the TL072 is probably getting harder to find as time goes on. (just a guess, haven't looked yet). im hoping this is true since i already have a few TL082's around here.
I also plan on using 1N6263 schottky diodes in mine. (yes, they will be matched up)
now, as for the 7.8mhz IF filter, this is the same concept used in Lou Franklin's "channel guard" filters he used to sell.
As a matter of fact, the schematic you posted is the same design as he used to sell.
I've seen it around the net for a while, and it does work well.
The thing is, yours looks different!
six resistors instead of four, and electrolytic on the board, and an LED?
what the heck is the LED for?
I have one of these and have put it in a couple of different radios, and i did like the performance.
CBphreaker, since you are all about the hi fi audio; have you noticed any adverse effects as far as audio bandwidth is concerned by having the narrower skirts in the IF?
another question i have is that since you replaced C47 with the crystal filter, is the radio more narrowbanded with regards to receive gain over say 128 channels?
I ask this because one of the most popular mods for broadbanding the receive in this chassis is to replace C47 with a 3-5pF cap. im sure you can see what im getting at.
again, i see no need for special test equipment here beyond what one uses to align a radio.
When it comes to breadboarding up circuits from schematics, the truth is that either you are up for the challenge or you are not, and aside from selling a kit with silkscreened part designators on the PC board, those that can build a circuit off of a schematic will be interested, and those that can't, won't.
I don't think it's something you can learn how to do from just a youtube video.
you have to jump in, buy some parts, and get to soldering.
then, when the light doesn't come on, find out why.
eventually, with enough trial and error, you learn certain concepts with regard to circuit layout that will help you along the way. you also learn about a product called stripboard that will change you life! LOL
CBphreaker, I see that you also run a FET in your D104!
I use a JFET (MPF102) to get the ultra high input impedance, and don't bother using a second stage. I didn't design the circuit, it's something i found online, i just figured out a way to use the PC board in my silver eagle to accommodate this circuit.
I agree that it really helps the low freq response of the MC320 element.
lastly, i wanted to ask you about your line out circuit, as i built one for my madison(8719).
Mine just taps off the high side of the volume control, and uses a TL082.
I am no circuit designer, and got this circuit from a friend who does not want me to post the schematic. I will say that it is online, but that's all i can say.
so, if i wanted to run your AM detector circuit, can you see any problems from letting it feed the stock volume control like usual, and my line out being tapped off of that?
Im sure there is more i want to ask you, but i'd better stop there. LOL
This kind of stuff is what i live for, so please know that your responses will be actually utilized to build this.
LC
PS- just wanted to add that it sure looks like there are a lot more components on your AM detector board than there are on the schematic.
can you draw a schematic of what you have built, or give some details about what you changed and why?
it also looks like you used a 10K pot instead of a 5K.
so much to discuss!
To start with, on the low distortion AM detector circuit (the coolest part of this to me), i'm not seeing where any test equipment is necessary.
from the description given in the link, it sounds like you just lift a component lead to disable the AGC (not sure which one yet, as i haven't looked at a 148GTL schematic yet to find it)
Then tune the pot on the detector board by ear and using the radio's S-meter.
from the way he describes it, there should be a definite "sweet spot" with that pot and should be attainable by ear.
Please let me know if i am mistaken about this.
I would think that a TL082 could be used here, as the TL072 is probably getting harder to find as time goes on. (just a guess, haven't looked yet). im hoping this is true since i already have a few TL082's around here.
I also plan on using 1N6263 schottky diodes in mine. (yes, they will be matched up)
now, as for the 7.8mhz IF filter, this is the same concept used in Lou Franklin's "channel guard" filters he used to sell.
As a matter of fact, the schematic you posted is the same design as he used to sell.
I've seen it around the net for a while, and it does work well.
The thing is, yours looks different!
six resistors instead of four, and electrolytic on the board, and an LED?
what the heck is the LED for?
I have one of these and have put it in a couple of different radios, and i did like the performance.
CBphreaker, since you are all about the hi fi audio; have you noticed any adverse effects as far as audio bandwidth is concerned by having the narrower skirts in the IF?
another question i have is that since you replaced C47 with the crystal filter, is the radio more narrowbanded with regards to receive gain over say 128 channels?
I ask this because one of the most popular mods for broadbanding the receive in this chassis is to replace C47 with a 3-5pF cap. im sure you can see what im getting at.
again, i see no need for special test equipment here beyond what one uses to align a radio.
When it comes to breadboarding up circuits from schematics, the truth is that either you are up for the challenge or you are not, and aside from selling a kit with silkscreened part designators on the PC board, those that can build a circuit off of a schematic will be interested, and those that can't, won't.
I don't think it's something you can learn how to do from just a youtube video.
you have to jump in, buy some parts, and get to soldering.
then, when the light doesn't come on, find out why.
eventually, with enough trial and error, you learn certain concepts with regard to circuit layout that will help you along the way. you also learn about a product called stripboard that will change you life! LOL
CBphreaker, I see that you also run a FET in your D104!
I use a JFET (MPF102) to get the ultra high input impedance, and don't bother using a second stage. I didn't design the circuit, it's something i found online, i just figured out a way to use the PC board in my silver eagle to accommodate this circuit.
I agree that it really helps the low freq response of the MC320 element.
lastly, i wanted to ask you about your line out circuit, as i built one for my madison(8719).
Mine just taps off the high side of the volume control, and uses a TL082.
I am no circuit designer, and got this circuit from a friend who does not want me to post the schematic. I will say that it is online, but that's all i can say.
so, if i wanted to run your AM detector circuit, can you see any problems from letting it feed the stock volume control like usual, and my line out being tapped off of that?
Im sure there is more i want to ask you, but i'd better stop there. LOL
This kind of stuff is what i live for, so please know that your responses will be actually utilized to build this.
LC
PS- just wanted to add that it sure looks like there are a lot more components on your AM detector board than there are on the schematic.
can you draw a schematic of what you have built, or give some details about what you changed and why?
it also looks like you used a 10K pot instead of a 5K.
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