[Kenwood] Ref: TS-850S Driver Bias Problems

Sun, 4 Jan 2004 15:38:22 -0500

Wouldn't it be more accurate, and probably safer, just to measure the
current through the resistor(s), or the voltage drop across the
resistors?? Resistors pass current so some of them will get warm or hot.
"...spot check how warm the resistors get while sending V's (be
careful and do not get a jolt). When not spot checking the heat of the
resistors, keep your fingers crossed that someone..." Dangerous to do and
how hot is hot? Hot to touch, burn the skin off your finger, etc. Never a
good idea to put any part of your body in close proximity to high voltage
current carrying components.

Pete, WA2CWA
ps Wasn't this an 830 we were talking about not an 850

On Sun, 4 Jan 2004 13:33:00 -0500 "Larry,  K4WLS" <[email protected]>
writes:
> I wish "self made" engineers would stop ruining good Kenwood
> rigs by tinkering with the driver and final components in order
> to reduce ALC to get a few more watts out on SSB, or change
> the final bias and screen voltage to get a few more watts out on
> CW. Doubling the output power of a rig only results in a signal
> increase of 1 S Unit on the receive end anyway (under the most
> ideal conditions).
> 
> Check schematic or board layout in service manual to determine
> the correct value and wattage rating of the darkened resistor. It
> has been damaged by heat, and the resistance is probably changing
> with heat and/or current. This is prob why the driver bias voltage
> is fluctuating. Replace the 100 K Ohm resistor with one of the
> correct value and wattage rating as per schematic/service manual.
> 
> Before replacing the 100 K Ohm resistor, it might be a good idea
> to make sure this resistor was not changed by a Tech Field
> Bulletin. Someone on the list who has had a TS-850S for a
> good while can verify the correct value of this resistor.
> 
> After doing this, remove the 12BY7A Driver tube, turn on the
> power and feel both resistors for a few mins to make sure they
> are not getting excessively hot. If OK, replace Driver tube, and
> do the same thing. If OK, check the driver bias and see if it OK.
> Turn on Fil switch to finals, set Drive Control fully CCW.
> Key in CW and adjust the Final Bias for the correct idling
> current.
> 
> With covers still off, connect rig to dummy load, Mode to CW,
> and 20M. Tune the rig with low power, and slowly increase
> Drive control to around 180 mA of plate (cathode) current.
> Re-check Plate Dip. Keep your nose close to the Driver board,
> 
> did not change the value of these two resistors in an attempt
> to correct a problem.
> 
> GL Pal - You Might Need It,   Larry   K4WLS
> 
> - - -
> 
> Your moderator for this list is:
> Larry Wilson KE1HZ [email protected]
> 
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