[R-390] R-390 Antenna Relay Chatter

Fri Oct 7 16:30:46 EDT 2022

Onewould have to assume that the Collins people who designed the R-390and the R390A knew what they were doing. True, the B+, like anyother voltage, will rise as the load is decreased. But I amconfident that this rise was accounted for in the original designs bycompetent engineers.
Asfor AC line voltage increasing over the years, this is simply amisunderstanding of the line voltage conventions which started wayback in 1927 with the beginning of AC powered radios.
Whenthe Edison Three Wire DC Distribution System was adopted for use withAC, there were two voltagechoices for AC powered devices in the home. In the very beginningthese voltages were either115vac or 230vac. Overtime, as demand for electric power grew, more distributiontransformers were added to the local distribution system whichreduced IR losses and this reduced line voltage fluctuations.
115vac,117vac and 120vac line voltages are just voltage standards, used todifferentiate between the two Edison inspired AC voltages availableto the home and not the actual line voltage present at the "socket."One cannot expect the AC line voltage to remain at a steady statevoltage throughout the day under the varying loads presented to thedistribution system.
Theactual line voltages for the three standards are:115vac +/- 10% or 103vac to 127vac117vac +/- 7.5% or 108vac to 126vac120vac +/- 5% or 114vac to 126vac
Thethree rating standards above are the result of surveys done in the1920's, 1940's and 1960's by either NEMA (National ElectricalManufacturers Association) or other groups that also included NEMA orit's later incarnations. The purpose of these standards was to set arange of line voltages for equipment manufacturers that would beavailable across the country.
The"Ratings" page from the first NEMA standard in 1927 isenclosed. As you can see, themaximum line voltage was around 126vac from the very beginning of "ACSocket Power." Thelower line voltage limit and the resulting average voltage were theonly voltages that changed in all of the subsequent standards as this specification was tightened.

Asfor adding a resistance to a silicon diode to better mimic thevoltage drop of a Selenium rectifier, it is neither needed nordesired. Simply stated, the Selenium rectifier is a crappyrectifier. In addition to taking up so much more real estate it isgreatly affected by ambient and operating temperature.
Theaverage voltage drop of a silicon diode is one volt. The averagevoltage drop of a Selenium rectifier cell is also one volt. Becausemost Selenium rectifiers have a relatively poor reverse voltagerating, most Selenium rectifiers are a stack of four or more cells.
Thisthree volt increase in B+ by changing from Selenium to silicon is swamped by the normal line voltagevariation of the AC distribution system. If the goal in power supplydesign is to have decent voltage regulation then eliminating anyseries resistance will also reduce IR loss which is currentdependent, by definition.
Regards,Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy

-----Original Message-----
From: Les Locklear <leslocklear at hotmail.com>
To: David Wise <d44617665 at hotmail.com>; Barry <n4buq at knology.net>; R-390 Mailing List <r-390 at mailman.qth.net>
Sent: Fri, Oct 7, 2022 12:33 pm
Subject: Re: [R-390] R-390 Antenna Relay Chatter

>From the "Archives"

DO NOT use the "STANDBY" position on the FUNCTION switch. The now unloaded stages will cause the various voltages in the receiver to rise upwards perhaps beyond the tolerances of some critical components. This is caused by the multiplicity error in our sometimes 120v+ line voltage v/s the 115v in use when the 390A was designed and built. Since it is normal for the "LOCAL GAIN" control to not completely mute the audio when turned down fully, it is natural to consider putting the receiver in "STANDBY." Remember, DON'T. Instead, turn the audio down and also back off the RF GAIN control to about 11 o'clock and the residual audio will disappear and no damage will be done to the receiver.

Les Locklear
________________________________
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of David Wise <d44617665 at hotmail.com>
Sent: Friday, October 7, 2022 12:12 PM
To: Barry <n4buq at knology.net>; R-390 Mailing List <r-390 at mailman.qth.net>
Subject: Re: [R-390] R-390 Antenna Relay Chatter

Should not chatter.  #1 suspect is CR801; selenium rectifiers have a notorious habit of increasing forward resistance as they age.  Convert to silicon plus a resistor in series to mimic the natural forward resistance of new selenium.  (I don't know what that value should be.)  This is what Tektronix did with their oscilloscopes; for every selenium-powered model, they created a silicon retrofit kit.  One of my scopes has one.

Or you can add a reservoir capacitor, starting small and increasing until the chatter is reliably gone at low mains voltage.  I am using 100uF.  Upside is potentially reduced hum.  Downside is that CR801 will continue to deteriorate, so eventually the problem will recur.

HTH,
Dave Wise
SWL (inactive)
________________________________
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of Barry <n4buq at knology.net>
Sent: Friday, October 7, 2022 9:59 AM
To: R-390 Mailing List <r-390 at mailman.qth.net>
Subject: [R-390] R-390 Antenna Relay Chatter

When in STANDBY, the antenna relay in my R-390 produces a bit of chatter.  Is this normal?  I see where that relay is fed, unfiltered, from CR801 which, from the pictures in the manual, appear to be a stack of selenium diodes and I'm wondering if that rectifier stack might be a problem.  Anyone know what to expect from that relay in STANDBY and, perhaps, what I'm seeing might be normal?

Thanks,
Barry - N4BUQ
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