[R-390] filtering on R-390 C101, C103

[Jim Whartenby]

Jacques might be on target about leaky capacitors but it could just as easily be out of tolerance resistors associated with the 5651 voltage regulators, or both.  Then again, it should be noted that nothing might be wrong.  The 5651 voltage tolerance is just a smidge over 5%.  Two in series would have a total RMS tolerance variation of about 7.1%.  The 9 volts difference you report divided by 180 volts gives a tolerance 5%.  Yes, your voltage is at the low end of the spec but it is still within spec.  I don't believe the absolute voltage value of B+ is all that important but the voltage stability over time and temperature is important.
I might also add that ALL voltages mentioned in ANY manual are NOMINAL values, not absolute.  There is always a tolerance associated with the voltage measured be it mentioned in the manual or not.  When you start adding the tolerances of several 5% resistors into the mix, the RMS value of the measured voltage can easily exceed 10% of the nominal value but still be in spec.  This was something that was pointed out in tech school at Keesler AFB when I was in school for Ground Radio back in 1968.  
The analog meters used back in the day usually had up to a 3% error which does not include the parallax error when reading the meter scale against the pointer position.  The DVM might have an absolute error of half a percent plus or minus a half digit rounding error.  Add to this the input impedance difference between an analog VOM (perhaps 20kohm/volt) to that of a DVM (perhaps 10 megohms) and you can get close to a 5% error in voltage measurement between the two meters.
Might also point out that an analog VOM is most accurate when laying down, not standing upright.Regards,Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Saturday, February 7, 2026 at 02:00:58 PM CST, Jacques Fortin <jacques.f at videotron.ca> wrote:   

 Hi Alex,
About your HV regulator output running at 171V: funny, because it's usually the reverse (running higher than 180V).
The only thing that can cause that, IMHO, is leakage in the C606.
If it is that, the control grid of the V607 goes higher than it is supposed to be, forcing the regulator output to run low.
Not having a reliable tube tester when "playing" with a R-390 is a difficult situation.
Try to locate someone that have one who can help you.
About the other components in the HV regulator circuit, and all the other ones (audio stages) in the same module: do not trust any.
The temperature goes so high in the chassis that IMHO, they all need to be changed for new ones, not only the 47 ohms resistors.
Once all those will be replaced by modern components, the 180V output should be good, unless the 5651 needs to be replaced also.

73, Jacques, VE2JFE in Montreal

Hello All,
Last night I was able to slowly bring the set up on my variac and - it works!  I was able to tune in a few stations, and everything appears to function, even the antenna relay!  I had to replace one dead 6082 tube in the regular circuit.  B+ measures 171.1 volts steadily at the J601 test point on the side of the chassis, with basically no fluctuation.
Is  171 volts this too low for the B+?  According to the manual it should be 180 volts.  Could this be caused by weaker rectifier or VR tubes?
What is next?  My thought was to replace the 8 47ohm resistors - 4 each in the power supply and audio modules.  Unfortunately I do not have a reliable tube tester.
Thanks,
-Alex

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