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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: May Mon 01, 2017 7:01 pm 
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Joined: Jan Mon 12, 2009 7:38 am
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Location: homestead, fl
Or the stock supply is just running out of gas. Seen that in cheap 70's audio gear. Lousy PSU = increased noise.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: May Mon 01, 2017 10:15 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17981
Location: Warner Robins, GA
True.

I've often found a large filter cap usually takes care of that for the most part for things that only need a little help, but if that don't work a more capable power supply is necessary.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: May Tue 02, 2017 1:56 pm 
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Mostly hum can be traced to the RF in AC power lines being picked up by receiver... This is usually why some radios may have issues and not others... Carefully orienting transmitting antenna away from power lines often reaps great rewards...

For P/S it's easy enough to look B+ with scope and see if it's dirty...


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: May Tue 02, 2017 5:09 pm 
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Joined: Jan Mon 12, 2009 7:38 am
Posts: 955
Location: homestead, fl
35Z5 wrote:
Mostly hum can be traced to the RF in AC power lines being picked up by receiver... This is usually why some radios may have issues and not others... Carefully orienting transmitting antenna away from power lines often reaps great rewards...

For P/S it's easy enough to look B+ with scope and see if it's dirty...


good point on scope, gonna try that. im gonna be a bit busy this week so wont have much time to experiment but this TH thing has been a longterm project with me. have 5 of them here so no fear if i trash one accidentally while hacking.

if we could only get a schematic to these darn things...


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Sun 01, 2017 2:52 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1084
Location: Tucson AZ
There is a fellow local to me that has 3 new 4.6 units for 50 each. I'm really tempted to get one.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Fri 20, 2017 3:17 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1084
Location: Tucson AZ
Cleaned up A LOT of hum by disconnecting a ground wire that connects between the ground pin on the AC plug and the rectified output circuit board in the wall wart for the unit.


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Fri 20, 2017 4:11 pm 
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Sometimes hum is less without a ground...

I wired the ground for one of my tube units thru a switch, can flip it back & forth to check what's best... It can vary day by day depending on how wet the roof is, what's in operation etc... Since I moved transmitter out to garage I rarely switch it, rainy day and a little hum, not worth getting wet to correct... Maybe one day I'll wire it to a relay controlled by a garage door remote receiver... Ummm, naah that ain't likely...


Tom


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 Post subject: Re: Talking House AM Transmitter MODIFICATION IDEAS HELP?
PostPosted: Oct Sat 21, 2017 1:36 pm 
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Location: Warner Robins, GA
35Z5 wrote:
Sometimes hum is less without a ground...

I wired the ground for one of my tube units thru a switch, can flip it back & forth to check what's best... It can vary day by day depending on how wet the roof is, what's in operation etc... Since I moved transmitter out to garage I rarely switch it, rainy day and a little hum, not worth getting wet to correct... Maybe one day I'll wire it to a relay controlled by a garage door remote receiver... Ummm, naah that ain't likely...


Tom


Agreed.

Also depends on the radio.

My R-390 hums less with the ground lift switch one way and my RCA K-80 console in the same room hums less with the switch in the other position.

I also took mine and installed a transformer so I could have a balanced or unbalanced line connected and used one of those isolated 1/4" jacks so that the only ground is through the ground prong on the power plug.

That seemed to tame hum somewhat.


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