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ART13 Audio mods




 
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Author Topic: ART13 Audio mods  (Read 701 times)
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w1vtp
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« on: April 06, 2018, 02:34:06 PM »

I was talking to Timmy HLR this morning about making some audio mods the a stock ART13 for a better sound.  I'm posting this schematic that came out of  our discussion with some omissions due to my not following him. I think I got the caps located that need to be "fattened up" and two that need to be removed (circle with a cross)

See attached schematic of the audio section

Al


* ART13 AUDIO MODS.gif (166.18 KB, 1056x816 - viewed 131 times.)
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W3RSW
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Rick & "Roosevelt"


« Reply #1 on: April 06, 2018, 03:28:30 PM »

Tnx, good stuff.
Id also increase C126 in lower left (plates and screens HV divider) from 2 uf to at least 20uf,  maybe up to 40 if it will fit.
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RICK  *W3RSW*
Jim/WA2MER
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« Reply #2 on: April 07, 2018, 08:03:14 PM »

I will be at NEAR-Fest, and that will probably provide a good opportunity to corner Tim about his suggested mods. I'll bring a schematic with me. - Jim
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Todd, KA1KAQ
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« Reply #3 on: April 09, 2018, 09:42:36 AM »

It's generally a good bet that the coupling caps will need to be fattened up to .1 from .01 uf. The latter were used to improve 'talk power' at the expense of fidelity, which wasn't a concern so much in wartime. Collins did the same thing in later transmitters. It was all about recoverable audio. This is one of the notable changes made to the KW-1 about halfway through production.
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WA1QHQ
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« Reply #4 on: April 09, 2018, 04:05:51 PM »

Al,

I had to bypass T201, the input transformer due to lots of hum. I am not sure if the transformer was defective or if it was just my audio set-up. You do not need T201 anyway just cap couple into the first audio stage. Also fatten up the coupling and bypass caps and she will sound real good.

Mark WA1QHQ
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Jim/WA2MER
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« Reply #5 on: April 09, 2018, 05:29:49 PM »

Todd: fattening up the coupling caps is a no-brainer and is already on my list of things to do. Tim seems to be suggesting to use the sidetone amplifier to increase mic gain and avoid having to use an outboard mic preamp, which is what I'm currently doing with an Applied Research and Technology Tube MP preamp (very cheap, but it does the job). I'm not sure I'm sold on the idea of repurposing the sidetone amp, there are a few things I want to address with Tim about it. Just looking for his thoughts, as well as yours and anyone else's who cares to offer an opinion. Much appreciated.

Mark: I don't seem to be experiencing any noticeable hum on my audio, but I will be sure to give a careful listen for it. Nothing is readily apparent on my scope.

Jim
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Anything worth doing is worth doing to excess.
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W2JBL
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« Reply #6 on: April 25, 2018, 05:50:47 PM »

Al- see my post in the new military radio section. Probably the same as what Tim did. Modified Heising (external to the rig) helps the low end a ton too.
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