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Another NC-303 Question...




 
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W3MMR
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« on: May 29, 2019, 09:17:29 PM »

So, after using the 303 on the band for a week or so and more guys finding out I have it, its been recommended I take the audio right off the detector. How much would it benefit from taking the audio directly from the AM detector and feeding an external amplifier? And if it's a worthwhile modification, would I take it from the output of the 6AL5, or the input to the 6AQ5? This would be the first time doing this mod to any rig, and this is my first boat anchor receiver so, any detailed info would be greatly appreciated. Thanks!

Perry
W3MMR
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** Studio "A" - Anan 200D, Shure SM7B, AL80BX, Internal & External Processing <--> Studio "B" - Heath-Kit DX100, D-10/4, National NC-303 **
KK4YY
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« Reply #1 on: May 30, 2019, 12:22:10 AM »

To use an external audio amp, probably the easiest way is to tap off the AF gain pot through a capacitor (0.1uf 400V film cap should be ok). The pot is easy to find, it will work in all modes, and preserve all the radios features.

In the NC-303 that pot appears to be at the input to the first audio stage, so it will be a very low level. You'll need an amplifier with sufficient gain. It's easy enough to try with a few clip-leads. If you like the result, heat up the soldering iron.


Don
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W3MMR
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« Reply #2 on: May 30, 2019, 08:26:25 PM »

Yeah after looking at the schematic I was thinking that picking off the center of the AF gain pot would probably be best since it comes right out of the 12AT7 AF Amplifier. Time to give it a try and see what happens!
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** Studio "A" - Anan 200D, Shure SM7B, AL80BX, Internal & External Processing <--> Studio "B" - Heath-Kit DX100, D-10/4, National NC-303 **
KK4YY
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« Reply #3 on: May 31, 2019, 07:35:20 PM »

Maybe I'm looking at the wrong schematic, but the pot appears to be at the input of the 12AT7. No matter, it's a good place to start.


Don
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