[TenTec] TT Scout on batteries?

[KF6ZZ@aol.com]

In a message dated 00-12-10 11:58:17 EST, you write:

<< Sounds to me as if the Scout has a 7810 or LM340-10 regulator for the VFO. 
That regulator needs about 2.5 volts headroom input to output to maintain 
regulation. Very likely the TO-92 version 78L10. 
I have no Scout and no scout manual to see. 
Perhaps that regulator could be replaced by a LM2937ET-10 or LM2940-10 or a 
series resistor and a TL431 family programmable zener diode. The LM29xx 
family works with down to
 0.6 volts drop, the TL431 would work lower though a bit less efficiently 
than the series regulator. The TL431 programmable zener diode is a far better 
regulator than any plain zener diode. 
 73, Jerry, K0CQ  > >

  The Scout uses the LM-2940 in the T0-220 package of  to develop a nominal 
10 vdc regulated power for the entire radio. The LM-2940 is located on 
connector 5 of the Receiver Control Board P/N 81644 .
The PTO is only one of several circuits that draws from this internal 10 vdc 
bus. 
The Scout manual specifies minimum operating voltage of 12 volts.

Perhaps the low voltage problem is brought on by the confluence of all the 
voltage drops in cabling and connectors   ( both external and internal )   
enroute to the  LM-2940.
  I have always been rather unimpressed at the chinzy power connectors used 
in  TT transceivers.    I have measured 0.5 volts drop across my Scout 
connector ( key down at 50 Watts out ),  and another 0.6 v drop across the 
fuse.   Thats a  1.1 Volt drop before the power even gets to the radio !

A bit excessive don't you think ?

Connectors and fuses really do have finite resistance that can devour 
marginal voltage reserves.

   It might be prudent to measure the DC voltage across the pins of the Scout 
power connector just inside the back panel of the Scout (during key down 50 
watt Transmit conditions) to observe just how much of the already low battery 
voltage has been further reduced by the connections. 

  73,                              
  -  Phil     KF6ZZ

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