[MRCA] April 23 PRC-47 no transmit update

[Ray Fantini]

The voltages will read higher without the tube in the circuit. Other than swapping the tube there is no good test. As crazy as it sounds you can check from filament to any other pin on the tube and there will be no resistance with a good tube. Although this is not an ideal test being when the tube has the filament on sometimes it shorts then and with it off reads good. In the real world beyond substitution you would use a Megger or Hi Pot tester, also don't forget to look from control and screen grid to plate for shorts being that will cause issues too.

Ray F/KA3EKH


-----Original Message-----
From: mrca-bounces at mailman.qth.net [mailto:mrca-bounces at mailman.qth.net] On Behalf Of James Green
Sent: Monday, April 23, 2018 3:10 PM
To: mrca at mailman.qth.net
Subject: [MRCA] April 23 PRC-47 no transmit update

I measured the PL-177 plate tube B+ at J101 with the tube installed & a 5 amp slow blow fuse in the 20 amp fuse holder.  The fuse blew. I next put in a 10 amp slow blow fuse. This did not blow. I measured B+ Low at 810 VDC and Hi at 1,810 VDC Both are higher than expected. Lo should measure 650 VDC and Hi should measure 1,500 VDC.

I was just wondering if I had a shorted PL-177 tube. How does one determine this?
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