Sears amplified desk schematic

[Copycat32]

Hi all I received a Sears amplified desk Mic looks like a turner plus 3 B but all plastic and totally different guts not working someone had their fingers in it looking for a schematic or pics of the inside of anybody has one
Thank You

 

[ChromeCobra]

I don't know about the turner plus but I used this schematic to fix my brother's d104 it would possibly get you started somewhere for your mic here is the link http://www.nucow.com/Microphones Lamps/vintage microphones/D104 schematic.htm hope this helps you

 

[Greg T]

A model number and/or pic would be good.

 

[ChromeCobra]

I will see what I can find for ya

 

[ChromeCobra]

Here is what the site said "I found a schematic of the Turner +3 mic online. It is more advanced than you should think as Turner already implemented compression in the late seventies. They called the compression technique “modu-guard”. It is a rectifier circuit that rectifies the audio and sends a DC attenuation signal back to Q3 in the source of the FET amplifier."

 

[VMC]

Aiiiiiyiyiyi.... DC through a pot

 

[ChromeCobra]

I'm learning electronics and I was just trying to help the original guy that made the post fix his microphone can you tell me why it's a bad idea to have the DC going threw the Variable pot I have found out that they don't like current poof magic smoke I am trying my best to learn radio it is my passion always wanted to be a Radio DJ cause I was told I have the voice

73s Chrome Cobra Tennessee

Oh PS
I know this ain't the place but I want to make a tube amp yes I know there is deadly high voltages cause I had a old tube amp that Checo gave me and it's didn't have a bottom on and I forgot one night while moving stuff on the bench and I got a shock and my arm went numb the weirdest feeling ever not feeling your arm anymore

 

[brandon7861]

Aiiiiiyiyiyi.... DC through a pot

Most pots do have DC through them. Its no different than any other resistor. Lets say its a 1/20 watt 5k pot and a 9v battery running that amp circuit. Also assume for a conservative estimate that Q2 is fully on and the 220ohm and 330ohm are the only other things in series with the pot for a total of 5550 ohm. 9v/5550=0.00162A. So we know the pot will never see more than 1.62mA of current through it. From this we also know the voltage across the 5k pot, which is 1.62mA*5k=8.11v. Now we know the voltage across it and the current through it, and therefore we know the power dissipated in it. 8.11v*1.62mA=13.13mW. 1/20w is 50mW, more than enough. The pot survives.

In real life, Q2 is not fully on, probably biased somewhere in the middle, and is adding resistance to that path further decreasing the current through it. That pot is nowhere near being damaged.

edit: The pot doesn't care if it is AC or DC. You give it enough power, it goes up in smoke. Ohms law applies exactly the same.

 

[nomadradio]

Biggest problem with DC on a pot is to have DC current through the wiper along with the audio. C10 makes sure the wiper has only audio passing through it. The DC current from end to end is a common design trick, and won't cause issues the way that passing DC through the wiper can do.

73

 

[VMC]

Most pots do have DC through them. Its no different than any other resistor. Lets say its a 1/20 watt 5k pot and a 9v battery running that amp circuit. Also assume for a conservative estimate that Q2 is fully on and the 220ohm and 330ohm are the only other things in series with the pot for a total of 5550 ohm. 9v/5550=0.00162A. So we know the pot will never see more than 1.62mA of current through it. From this we also know the voltage across the 5k pot, which is 1.62mA*5k=8.11v. Now we know the voltage across it and the current through it, and therefore we know the power dissipated in it. 8.11v*1.62mA=13.13mW. 1/20w is 50mW, more than enough. The pot survives.

In real life, Q2 is not fully on, probably biased somewhere in the middle, and is adding resistance to that path further decreasing the current through it. That pot is nowhere near being damaged.

edit: The pot doesn't care if it is AC or DC. You give it enough power, it goes up in smoke. Ohms law applies exactly the same.

Noise considerations, not power. Been a pro audio tech for 42 years and ones with DC all go noisy. Nothing control cleaner can't handle, but can be avoided with a couple caps.