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 Post subject: Philips Philetta hum through phono input
PostPosted: Dec Sun 24, 2017 1:38 pm 
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Joined: May Fri 11, 2012 1:26 pm
Posts: 467
Location: Ashland, MA
Hello forum. I restored a Philips Philetta BD273U and shipped it to someone. He says the AM/FM works fine but the aux input makes a hum. Doesn't matter what aux source he uses. I'm thinking it's a grounding problem with the cord I made. It was fine before I shipped it, but it was home-made so maybe it got kinked or something during packing/unpacking. I can make another cable but was wondering if there are other possibilities the buyer can check. Here's a video the buyer made of the problem:

https://www.youtube.com/watch?v=L_Op8CD ... e=youtu.be


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 Post subject: Re: Philips Philetta hum through phono input
PostPosted: Dec Sun 24, 2017 2:23 pm 
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Joined: May Sat 12, 2012 1:33 pm
Posts: 1692
Location: Rochester, NY.
I would suspect a poor ground first. These are the European/DIN style and not the RCA style jacks, correct?


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 Post subject: Re: Philips Philetta hum through phono input
PostPosted: Dec Sun 24, 2017 4:51 pm 
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Joined: May Fri 11, 2012 1:26 pm
Posts: 467
Location: Ashland, MA
Wally58 wrote:
I would suspect a poor ground first. These are the European/DIN style and not the RCA style jacks, correct?


Right, the kind with two banana plugs (I used a single euro power outlet adapter for that end). He says he can hear the music when he plays it through the external speaker port (albeit not amplified) so the cord is probably fine and it's a problem with the aux circuit. You have to push down the two shortwave buttons simultaneously to activate the aux circuit. Does this jive?


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 Post subject: Re: Philips Philetta hum through phono input
PostPosted: Dec Sun 24, 2017 5:19 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 37474
Location: Livermore, CA
Could signal line and ground be reversed?

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Norm


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 Post subject: Re: Philips Philetta hum through phono input
PostPosted: Dec Sun 24, 2017 6:08 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5685
Location: Near Brandon, Iowa
Can also be a problem with the audio source, if it is AC operated. Try to determine the exact type of source being used, and ask that a battery-operated-only source (such as an iPod) be tried instead to see if it abates the hum (it may or may not, depending on how the hum pickup is occurring).

If this radio has U-prefix tubes, it is power transformerless which can complicate hookup to an AC powered signal source (the radio's phono port was designed to be used with a floating crystal or ceramic pickup).

IMO this problem isn't your responsibility to solve. It sounds like the radio works as it was designed to do sixty years ago. Tell your customer to try it with a crystal-pickup (unamplified) turntable and see how it works.


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 Post subject: Re: Philips Philetta hum through phono input
PostPosted: Dec Sun 24, 2017 10:02 pm 
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Joined: May Fri 11, 2012 1:26 pm
Posts: 467
Location: Ashland, MA
Norm Leal wrote:
Could signal line and ground be reversed?


Tried that...no joy.


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 Post subject: Re: Philips Philetta hum through phono input
PostPosted: Dec Sun 24, 2017 10:05 pm 
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Joined: May Fri 11, 2012 1:26 pm
Posts: 467
Location: Ashland, MA
lorenz200w wrote:
Can also be a problem with the audio source, if it is AC operated. Try to determine the exact type of source being used, and ask that a battery-operated-only source (such as an iPod) be tried instead to see if it abates the hum (it may or may not, depending on how the hum pickup is occurring).

If this radio has U-prefix tubes, it is power transformerless which can complicate hookup to an AC powered signal source (the radio's phono port was designed to be used with a floating crystal or ceramic pickup).

IMO this problem isn't your responsibility to solve. It sounds like the radio works as it was designed to do sixty years ago. Tell your customer to try it with a crystal-pickup (unamplified) turntable and see how it works.


He tried an mp3 player and the problem was still there. Also happens when he touches his finger to the source end of the plug. It does have U-tubes, which I've had problems with in the past. My guess is that something got knocked around in shipping, so maybe not my responsibility (I packed very well) but I'd still like to help the guy out if I can.


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 Post subject: Re: Philips Philetta hum through phono input
PostPosted: Dec Sun 24, 2017 11:49 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5685
Location: Near Brandon, Iowa
craterranch wrote:

He tried an mp3 player and the problem was still there. Also happens when he touches his finger to the source end of the plug. It does have U-tubes, which I've had problems with in the past. My guess is that something got knocked around in shipping, so maybe not my responsibility (I packed very well) but I'd still like to help the guy out if I can.

Ask the owner of the radio to disconnect the audio source cable from the radio and instead plug in a very short length of wire (lamp cord will do) from the "hot" aux port to the ground port. Then put the radio in "aux" mode and assess if the hum is still present. If it is, the problem has to be in the radio (however unlikely that is). No hum= radio OK.


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 Post subject: Re: Philips Philetta hum through phono input
PostPosted: Dec Mon 25, 2017 2:21 pm 
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Joined: May Fri 11, 2012 1:26 pm
Posts: 467
Location: Ashland, MA
lorenz200w wrote:
Ask the owner of the radio to disconnect the audio source cable from the radio and instead plug in a very short length of wire (lamp cord will do) from the "hot" aux port to the ground port. Then put the radio in "aux" mode and assess if the hum is still present. If it is, the problem has to be in the radio (however unlikely that is). No hum= radio OK.


Ok, but isn't that kinda what happens when he touches his finger to the ext. source end of the cable, that is, completing the circuit?


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 Post subject: Re: Philips Philetta hum through phono input
PostPosted: Dec Mon 25, 2017 6:50 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5685
Location: Near Brandon, Iowa
craterranch wrote:
lorenz200w wrote:
Ask the owner of the radio to disconnect the audio source cable from the radio and instead plug in a very short length of wire (lamp cord will do) from the "hot" aux port to the ground port. Then put the radio in "aux" mode and assess if the hum is still present. If it is, the problem has to be in the radio (however unlikely that is). No hum= radio OK.


Ok, but isn't that kinda what happens when he touches his finger to the ext. source end of the cable, that is, completing the circuit?

No, it's not the same. The objective of the above test is to determine if only the radio is at fault, not the radio OR the cable. It's necessary to remove as many "unknowns" from the problem as possible.


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