Cobra 148 side mic

[linearone]

Where is everyone picking up 8v for their echo boards?

 

[BC Coyote]

I wouldn't be caught dead running echo. But that's just me.........
Quickest and easiest way to get 8 volts would be to run a 7808 regulator off one of the 12 volt rails. Don't forget to put a cap on the input and output of the reg.
7.5 volt zener would work just as well.

 

[SuperLid]

Where is everyone picking up 8v for their echo boards?

IC4 8 volt regulator MB3756 Pin 1

 

[linearone]

IC4 8 volt regulator MB3756 Pin 1

Thank you!

 

[9C1Driver]

Just get a 2018 Extreme echo mic, done. This way the radio stays untouched.

 

[nomadradio]

And if you run any additional power a mike with electronics inside it becomes a RF feedback risk.

Doesn't mean it will squeal, but consider Murphy. An internal echo board is pretty well shielded from this kind if nuisance.

Pin 1 of the MB3756 is the pin at the end of the chip nearest the rear of the radio.

73

 

[BC Coyote]

if you run any additional power a mike with electronics inside it becomes a RF feedback risk.

Bang on Nomad ! The more stages of amplification and processing before the radio, the higher the chance of squeal, hum and hiss getting into the transmitted audio.
As well, more devices = more patch cables, and those are also huge generators of squeal hum and hiss.
The best sounding stations are running just a high quality power mic plugged directly into the radio. Endless racks of audio gear are not required and are often detrimental to audio quality.

 

[Shockwave]

Thank you!

That radios 8 volt regulator could be 40 years old, isn't made anymore, and is becoming a common failure. I would be hesitant about adding more load to that regulator and as previously mentioned, just install a three-terminal 8 volt regulator.

When the MB3756 starts to fail, you notice it first on the switched 8 volt TX side. It causes garbled audio in both SSB and AM transmit. Minor cases may appear like rapid shifts in transmit frequency on sideband. Severe cases will be completely unintelligible and heavily distorted even on AM, as the VCO and PLL constantly attempt to make rapid corrections in transmit.

Eventually the red transmit LED will fail to come on, with the total loss of the 8-volt TX line. While the part originally had ample headroom, it was not designed to last four decades. Any additional loading, accelerates failure. Radios that have their sideband bias turned up, are often the first to have this failure, since the TX 8 volts supplies bias in transmit too.