[R-390] R390 B+ Expected Tolerance

[Jim Whartenby]

Barry
The R-390 Finial Engineering Report, 15 Sept 1953, page 14, aka pdf page 19Input voltage variation +/- 15% results in a B+ change of +/- 1 volt maximum.Load current from 100mA to 200mA results in a B+ voltage change of +/- 2 volts maximum.

The 5651 voltage variation is 87 volts +/- 5 volts.  Current change through the 5651 from 1.5 mA to 3.5 mA results in a 3 volt maximum change.
Besides the resistors you have mentioned, a leaky C608 will also cause problems per Dave Medley.https://cvths.org/radio/r390/docs/misc_R390-URR_R391-URR.pdf

Jim

 
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy

-----Original Message-----
From: Barry <n4buq at knology.net>
To: R-390 Mailing List <r-390 at mailman.qth.net>
Sent: Sat, Nov 12, 2022 8:58 pm
Subject: [R-390] R390 B+ Expected Tolerance

I discovered that the regulated B+ is running about 175v instead of 180v in my R390.  I found R625 had drifted from 1k to 1.2k and, since I think that was originally a 1%, I replaced it.  I now get very close to 3.7k at the cathode of V609; however, that didn't change the regulated voltage.

I have five 5651s and except for one of them, virtually any two will produce 175v.  If that fifth tube is in place, I get about 185v.  According to my Hickok 752A, the fifth one appears to have a different current draw at its regulating voltage and that might account for the difference.

I have a spare 6082 that I've tried swapping in either socket with no differences there either.

Running at 115VAC input and getting close to 300v unregulated input to the regulator.

It leaves me curious as to how close to 180v is within specification.  I've searched the manuals and I can't seem to find a tolerance for that.  Anyone know?

Thanks,
Barry - N4BUQ
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