View Single Post
  #52   Report Post  
Posted to sci.electronics.repair
Winston Winston is offline
external usenet poster
 
Posts: 3,444
Default Grundig AM/FM portable "Transistor 305" troubleshooting

Sylvia Else wrote:
On 12/03/2012 12:05 PM, klem kedidelhopper wrote:


(...)

Was it with 7.50V applied or 9.0V? Lenny


There's a note on the schematic that they're measured with a battery voltage of 7.5V.


That looks like a typo.

R46 will drop 100 mV for every milliampere of battery current.

The only way to get the specified rail voltage of
7.0 V at 20 mA (Medium Wave operation) is with a
battery voltage of 9.0. Similarly, it takes 8.95 V
of battery voltage to get 6.75 V at 22 mA on
the rail, specified for FM operation.

Using a vaccum tube volt-meter,
which you might have some difficulty obtaining now


I'm willing to believe that a modern multimeter is more
than sufficient for these measurements. My Fluke 189
has an input impedance of 10 M. I'm not too concerned
about the additional 82 nA it costs to use, for a 9 V measurement.




--Winston