[R-390] R390 B+ Expected Tolerance

[Barry]

Hi Jaques,

I should've said film caps, not paper.

Vishay MKT1813422254
and
Vishay MKT1813410255

Honestly, I'm tempted to put the original parts back in.  They're probably still good and may last even longer than these replacements.

I'm seeing some very different voltages at V607 and am going to pull the AF deck once again to see if I can determine why those are the way they are.  I do note that I'm not seeing 182V on the cathodes of the regulators and, with the 1.5V - 2.0V drop across the load balancing resistors (which, BTW, are running right around 50-ohms), accounts for a bit more of the "under-voltage".

As David Wise commented, 175V is probably well within tolerance and I'm picking at nothing but, just the same, it bugs me...

Yes - I have adjusted the HUM BALANCE per the manual.

Thanks,
Barry - N4BUQ

 Subject: RE: [R-390] R390 B+ Expected Tolerance

> Hello Barry,
> 
> When you mention "new paper caps" did you really mean paper-in-oil caps ?
> I do not trust any paper cap for a long time, except the sealed ones
> (Sprague Vitamin Q, for ex.)
> All "real", not vacuum sealed PIO caps develops leakage with time.
> Better to use Mylar (polyethylene) or polypropylene ones, especially for
> C608.
> 
> There are other causes that can make the output a little low in this
> circuit:
> R623 can be of an higher value than the tolerance range.
> One of the two voltage divider resistors R616 and R617 can be out of their
> tolerance range, or both.
> V607 can have a higher transconductance than the "mean" value.
> The sum of the voltage drops of V608 and V609 should be 170V: if it is
> lower, the output of the regulator will be lower as well.
> 
> Just curious: what is the brand of the 5651 you have there ?
> They vary by few volts from one maker to the other and when they age also
> (they tend to go up when they age).
> 
> If nothing wrong can be found in the resistor values and you are still
> unhappy with the 175V (which is not a bad result at all, IMHO), try to lower
> the value of R626.
> A 100K resistor bridged across the actual R626 should raise the output by
> few volts...
> Adjust value in consequence of the measured result.
> 
> Last comment: the HUM BAL. adjustment can "move" the output voltage also.
> Be sure to adjust for minimum AC voltage at the test point J601.
> 
> 73, Jacques, VE2JFE in Montreal