RCA 35x schematic question

[ttx450]

Not sure if this is the right area to post this?  what does the symbol that looks like a battery mean in the red circle?  Says bias for gain data. I know some old radios have a small coin batteries in circuit for bias.  the radio I am working on does not. appreciate if someone could explain the symbol in the circuit.  thks

[TimFox]

It means that you should connect an external 3V battery as indicated to force the AGC voltage to a fixed value when measuring the gain.

[ttx450]

It means that you should connect an external 3V battery as indicated to force the AGC voltage to a fixed value when measuring the gain.

that helps, kind of new to working on old stuff.  so this is used only to measure the gain.  Can I use a external dc power supply to do that?  working on a radio that looks to be passed around and fingered many times and does not work, so have to trace everything.  thks

[TimFox]

A DC power supply will work:  be careful of polarity.
Back in the day, 3V Zn-C batteries were readily and cheaply available.  A 3V lithium cell is the modern choice.

[ttx450]

A DC power supply will work:  be careful of polarity.
Back in the day, 3V Zn-C batteries were readily and cheaply available.  A 3V lithium cell is the modern choice.

thanks.. do you know if that is positive or negative 3v, schematic shows 3v?  maybe there is more reference material out there for this in the manual that I have not read.  I have not read everything, just have been going through schematic and cleaning up the underside.  Did not understand that reference.  I will read over before I put pwr to it and see if I can find more info relating to the 3v bias. thks

[TimFox]

The schematic clearly shows the positive end of the battery to circuit common (AC-DC sets, without power transformer, do not ground that directly), and the negative end to the AGC line.  When operating, the AGC line is typically -13V with respect to that circuit common, according to that region of the schematic.

[ttx450]

The schematic clearly shows the positive end of the battery to circuit common (AC-DC sets, without power transformer, do not ground that directly), and the negative end to the AGC line.  When operating, the AGC line is typically -13V with respect to that circuit common, according to that region of the schematic.

thanks tim. working my way across the the bottom, just about done.  kind of a mess.  keeping finger crossed