[Hallicrafters] Measuring Resistors

[Philip Atchley]

Hi,

I'll do the best I can to explain "Checking Resistors" in circuit.  Here is 
basically how I do it.  Keep in mind that this is only a guideline, YMMV.

1.  I first check them still soldered In the circuit.  Often, resistors in 
the plate, grid and cathode leads of vacuum tubes can be checked in circuit 
and will read accurately, IF there aren't any other resistive paths in the 
same circuit (I.E. A coil across them etc).
     A.  Good capacitors in the circuit will not affect the reading in any 
way.
     B.  Coils across the resistor will affect it, while coils in series 
will not (providing there aren't any other resistive paths).

2.  When checking resistors IN CIRCUIT:
    A.  If the resistor measures within 10%, you are usually good to go.  IF 
they read more than 10% HIGH in resistance, they should be replaced (20% if 
they have no "tolerance band" on the resistor).
    B.  If they measure more that 10% LOW (20% no tolerance band) in 
resistance, check for parallel paths OR disconnect one side of the resistor 
and recheck the Value.
    C.  Carbon resistors may go either UP or DOWN in Value.  Usually they go 
up, but one 'infamous' resistor in Viking VFO's is known for going down in 
value until it self destructs, taking the Voltage regulator etc with it.

IF a resistor looks charred, overheated or is cracked it should be replaced 
even if it DOES measure good, it's a time bomb in waiting.

TIP.  If disconnecting one end of a resistor to "double check" it's value it 
is often better to just cleanly "snip it" with cutters, measure it, and if 
good, resolder it with a "lap joint".  Unless you have done a lot of them in 
the past (I have), and you try to remove it intact from a tube socket pin 
etc you may overheat it or break the tube socket pin in the process.  If you 
overheat it with the soldering iron it is most likely to go out of tolerance 
anyway.

73 de Phil,  KO6BB
http://users.mercednet.com/beaconeer/
Merced, Central California, 37.3N  120.48W  CM97sh


----- Original Message ----- 

I have another question.

Whan checking resistors in old sets, to see if they are in tolerance, is the 
only way to check them with any accuracy to first remove one end. With both 
ends of the resistor soldered in place, in many cases isn't it in parallel 
with other components, thereby making the resistance measurment too low?

Thank you for your responses in advance.

Best,
DW Holtman
WB7SSN