[Hammarlund] HQ-170 A smokin

[Brian Harris via Hammarlund]

Bob,

For the moment you can disregard the capacitors around the wafer switch because chances are the V7 screen bypass capacitor C38 shorted, causing increased current through the screen resistor R69, causing it to get hot and go very low in resistance before it got so hot it opened or nearly opened. When the screen resistor was low in resistance, the screen voltage/current to V7 would be too high, which would cause the plate current to soar and possibly cause the plate resistor R70 to get hot and eventually open or nearly open.  These are classic behaviors.  


Brian Harris, WA5UEK 
cell 214-763-5977 
email cosmophone at yahoo.com 


On Friday, November 7, 2014 9:19 PM, Brian Harris <cosmophone at yahoo.com> wrote:
  




Brian Harris, WA5UEK 
cell 214-763-5977 
email cosmophone at yahoo.com 


 
> On Nov 7, 2014, at 9:33 PM, Robert Sauvan <rsauvan at beyondbb.com> wrote:
> 
> Hi all,
> After I feel everything is going well, another radio decides to take a dive on me. My HQ-170A
 started getting a hissing/crackling sound minutes after turning it on. I decided to try to find the culprit. So I put it on the test bench, turned it on and it started smoking. I couldnt find the exact spot but it was in the area of the V7 tube socket. After turning it off and then on again to see if I could find where it was smoking from, it decided not to act up in that way anymore, but the S meter no longer climbs as it always did as it warmed up. Decided to do some resistance checks. I started at the V7 tube pins and found some really high resistances at pin 5 and 6.Pin 5 is supposed to have 8.5K and it has a 500K reading. Pin 6 is supposed to be 68K and it has 800K reading. All other pins on that tube look to be OK. Both of these pins have wiring going to the wafer switch.There are numerous caps in this wafer switch. What would I do to continue finding the possible bad part? Any ideas?
> 
> Any suggestions
 would be greatly appreciated.
> 
> Thanks-Bob-W0YBS
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