[MRCA] April 20th Update #2 PRC-47 no transmit

[Tim]

Hi Jim - Not sure I am following all this but a couple of thoughts:

Running the 47 in low power mode, including tuning, should not blow the 5
amp fuse.  So it's good to keep it at 5 amps while you are doing all this.
I have seen the HV PS oscillator transistors short under fault conditions
and the 20 amp panel fuse was still good.  Beware...

Also, there is a built-in HV divider circuit in the PA compartment for
measuring the HV B+.  It is J101 on the PA compartment shield. I recall it
is a 10:1 divider.  The specified voltages for the PA are under load so
testing them without the tube installed could be confusing things, and
probably dangerous.  Especially to your meter...

FYI,,Tim
N6CC

On Fri, Apr 20, 2018 at 12:13 PM, James Green <jagreen3 at sbcglobal.net>
wrote:

> Seems I can measure grid voltage at V1, V2 & V3 at A3J1, A3J2 & A3J3 in
> transmit mode. I get expected results. I still haven't found a good way to
> get at the plate voltages.
>
> Items 12 thru 15 are ok
>
> Item 15 is measuring the B+ at the power output tube. I measured this tube
> out of circuit by clipping my Fluke 77 positive lead to the cap lead of the
> PL-177 tube. The Negative lead to ground. I should get 650VDC Low power and
> 1,500VDC hi power. I get around 840VDC low power. When I switched to hi
> power I got a snap! like I did before with the PL-177 in circuit that led
> me to replace the Xmit power switch. I examined the switch very carefully
> and saw no problems. Also, the 5amp fuse in the 20 amp holder did not blow.
> I proceeded with the high power B+ test and discovered my fluke will not
> measure over 1,000 VDC so it registered OL when I measured Hi power. I will
> be building a test circuit with 2 equal resistors in series. Measuring the
> voltage drop across one of them should be 1/2 the total voltage. I want to
> be safe about this so I am going to think it over very carefully before I
> proceed.
>
> I expect the high reading on low power will come down with the tube in
> circuit and a proper 50 load.
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