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

[Alex Hopper]

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



On Fri, Feb 6, 2026 at 12:15 AM Alex Hopper <ahopper0216 at gmail.com> wrote:

> Jacques - I didn’t want to be the one to say it, but thank you!
> Interestingly, most of the key differences are in the power supply/power
> management!
> -Alex
>
> Jacques Fortin <jacques.f at videotron.ca> schrieb am Fr. 6. Feb. 2026 um
> 00:13:
>
>> Hi John,
>> Ahem... The Alex concerns were about a R-390/URR, not a R-390A/URR...
>> Despite the two versions share the same fit, form and function, there is
>> significant differences between the two.
>>
>> 73, Jacques, VE2JFE in Montreal
>>
>>  Hi Alex - Good questionsI have attached two documents that will help you
>> in understanding how these power supply filtering caps are electrically
>> located in the power supply circuit.  I do hope you have acquired the
>> knowledge to read a schematic, if not this can be acquired.  Depending upon
>> the age and condition of the existing filter caps, I would treat them as
>> suspect and likely needing to be replaced, unless evidence from performance
>> validation shows otherwise.  While they might "operate", residual AC ripple
>> is not to your receivers advantage.  You will need to try to understand how
>> a power supply filter capacitor failure mode will likely result in
>> regarding what else you might then need to repair. The Y2K manual contains
>> a number of options exist regarding these filter capacitors.  If you power
>> these up outside of the receiver, give them a good session with slowly
>> increasing voltage and slowly increase current demand into a load such as a
>> 25 watt stove oven light bulb initially.  Monitor output with a scope if
>> you have one available.  The peak current is at first on cold inrush, once
>> warmed up the current is about ~~1.3 or so amps if I remember correctly.
>> Try to operate the receiver at 115 volts rather than the standard 126 volts
>> now on the US mains voltage using a variac and if available a 1:1 isolation
>> transformer.  Good luck \VR\John
>>
>>