knight kit t 60 help

[jer19541]

Have a VERY close look at that switch. Odds are it's built from wafers of brown bakelite plastic. If you saw where on the switch the arc came from, get a bright light onto that section and see if a black bridge has burned/formed between adjacent contacts. This happens a lot in other radios, but I'm just guessing about seeing that fault in this one.

73

Ok thanks for the help. N4tbu

 

[jer19541]

Have a VERY close look at that switch. Odds are it's built from wafers of brown bakelite plastic. If you saw where on the switch the arc came from, get a bright light onto that section and see if a black bridge has burned/formed between adjacent contacts. This happens a lot in other radios, but I'm just guessing about seeing that fault in this one.

73

I checked switch I noticed the brown wafer looked saturated with d oxit which I sprayed on over a year ago. Both wafers. I'm guessing this is a problem

 

[jer19541]

I checked switch I noticed the brown wafer looked saturated with d oxit which I sprayed on over a year ago. Both wafers. I'm guessing this is a problem

I checked switch I noticed the brown wafer looked saturated with d oxit which I sprayed on over a year ago. Both wafers. I'm guessing this is a problem

Also. The clasp that makes contact with the wafer foil. Is bent and in poor condition. Seen arcing from a rivet that holds the clasp on

 

[nomadradio]

Makes it sound more like your short circuit is passing through the switch.

Time to take a meter set for continuity with one lead clipped to ground, and poke lugs on the meter with the other probe ne by one. Rotate the selector while checking each lug. A spot that shows the short no matter where the selector is turned will be connected to your short circuit. The wires leading away from that lug will be your next target. Well, what's connected to the far end of those wires.

Touching the probe to a lug that only shows continuity at one or two positions of the knob gets you close to the short, but you want the lug that shows a short all the time, no matter where the knob is turned.

73

 

[jer19541]

Makes it sound more like your short circuit is passing through the switch.

Time to take a meter set for continuity with one lead clipped to ground, and poke lugs on the meter with the other probe ne by one. Rotate the selector while checking each lug. A spot that shows the short no matter where the selector is turned will be connected to your short circuit. The wires leading away from that lug will be your next target. Well, what's connected to the far end of those wires.

Touching the probe to a lug that only shows continuity at one or two positions of the knob gets you close to the short, but you want the lug that shows a short all the time, no matter where the knob is turned.

73

Thanks

 

[jer19541]

Makes it sound more like your short circuit is passing through the switch.

Time to take a meter set for continuity with one lead clipped to ground, and poke lugs on the meter with the other probe ne by one. Rotate the selector while checking each lug. A spot that shows the short no matter where the selector is turned will be connected to your short circuit. The wires leading away from that lug will be your next target. Well, what's connected to the far end of those wires.

Touching the probe to a lug that only shows continuity at one or two positions of the knob gets you close to the short, but you want the lug that shows a short all the time, no matter where the knob is turned.

73

Checked all lugs on function switch (10) no shorts to ground on any lugs

 

[jer19541]

used this transmitter for about a year worked very good. and then, recently turned it on standby and the 10 watt ceramic resistor gets very hot and will smoke. very noticeable hum from the transformer. any help or suggestions will be apprecieated. n4tbu

Also seen some arcing on function switch

The smoking resistor tells us that there is a short to ground on the B+ output of the power supply. Likeliest cause would be C29 if it's the original 60 year-old part. Next-most would be the 6DQ6 final tube. Unplugging the tube would clear the short if that's the cause.

But if the electrolytic capacitors are original, they are the most-likely failure risk.

And having it start after replacing the cord was just a happy coincidence. Don't see how to connect that hot resistor with a replacement power cord.

73

 

[jer19541]

Have a VERY close look at that switch. Odds are it's built from wafers of brown bakelite plastic. If you saw where on the switch the arc came from, get a bright light onto that section and see if a black bridge has burned/formed between adjacent contacts. This happens a lot in other radios, but I'm just guessing about seeing that fault in this one.

73

 

[nomadradio]

Looks like it's time to find this resistor on the schematic diagram and see where an overload would have to be connected to make it smoke.

73

 

[jer19541]

Looks like it's time to find this resistor on the schematic diagram and see where an overload would have to be connected to make it smoke.

73

Ok. Will check. Thanks again

 

[jer19541]

Ok. Will check. Thanks again

Clipped one end of. The resistor showed that end was shorted to ground. Found one diode had no continuity in either direction. I think I'm getting close

 

[jer19541]

Clipped one end of. The resistor showed that end was shorted to ground. Found one diode had no continuity in either direction. I think I'm getting close

Also. The other diode. Has no continuity in either direction. Removed diodes from radio before checking. ( 2)

 

[SuperLid]

used this transmitter for about a year worked very good. and then, recently turned it on standby and the 10 watt ceramic resistor gets very hot and will smoke. very noticeable hum from the transformer. any help or suggestions will be apprecieated. n4tbu

Caps? Shorted tube?

 

[jer19541]

Caps? Shorted tube?

Will check

 

[jer19541]

Caps? Shorted tube?

New caps. Removed. Tubes. No change. Same problem