[R-390] Fwd: Errors in the 'R-390 Cookbook'

[Jim Whartenby]

Larry
Point taken about the 6080.  Thanks for keeping up with the changes to the Cookbook.  Don, W5OR (SK) would be proud!

As for voltage measurements and such, it is always seems to be overlooked that 115vac is an average voltage, not an absolute.  Same for the 180 VDC regulated power supply.  Both have tolerances, the former caused by the normal variation of the AC line over the day (+/- 10% when the R-390 was designed) and the latter is caused by the 5651.  

The 5651 VR tube tolerance is +/- 5 volts so when in series, the absolute worst case voltage variation is +/- 10 volts.  The purpose of the  regulated power supply in the R-390 is to hold the B+ relatively invariant over the normal AC supply voltage range.  There is no voltage adjustment pot because the actual B+ voltage is not important.  The redesigned R-390A, of course, did away with regulated B+.   The current regulator should have also been dropped but the Signal Corps made it a requirement, so it lived on.

The TS-505 VTVM is specified as the voltmeter used to test and align the R-390.  It has a DC voltage tolerance of +/- 4% of full scale.  So the 200 volt range has an uncertainty of 16 volts DC at full scale.   For AC measurements, the tolerance is +/- 6% of full scale.  Modern DVMs have much better specs so I am sure that the modern test equipment is causing some panic when things are actually within specification.  

For test and alignment, the AC line tolerance for the R-390 is +/- 5% which gives a high value of 120.75 VAC.  So I would be more concerned with the heater voltage of all of the tubes in the R-390 / R-390A than in the line or B+ voltages.  Typically, receiving tube heater voltage tolerance is +/- 10% which guarantees that the tube will meet published specifications.  Today's line voltage average is 120 VAC +/- 5% so things are actually better now then in the day,

Regards
Jim