[R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
Jacques Fortin
jacques.f at videotron.ca
Thu Nov 7 23:26:38 EST 2024
Hi Jerry,
Ah ! IRC resistors...
No wonder that they failed.
If you crack the "rough surface" envelope, you will find a small glass tube in the middle, with a deposited layer of carbon.
Because the molding phenolic had let the moisture going to the carbon layer, it was slowly "eaten" by the oxidation, until it failed.
I cannot explain why they were assembled there instead of AB ones...
The industry knows since the WWII that they are short-lived components.
The MF ones you used as replacements, on the other hand, will outlive all of us...
Happy to know that you now have proper audio.
A NL stage that is not polarized (even in the OFF position) cannot "pass" any signal properly.
73, Jacques, VE2JFE in Montreal
-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de k1jos at att.net
Envoyé : 7 novembre 2024 22:30
À : r-390 at mailman.qth.net
Objet : Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
I think the R-390 is working at least 95% well. I replaced R544 (470k) and its identical adjacent resistor R541. R544 measured open, R541 was reading almost 1Meg so I figured why not. I have attached pictures because these 2 resistors were of a different type or manufacturer than most of the carbon comps in the radio. The other CC's look like typical Allen Bradley and had no physical signs of heat stress but these two had the older style of rounded edgers, rough surface texture and just looked like they had been cooked a long time.
Bottom line - my resistances and voltages for V507A and V510 are now very close to specs and most importantly the R-390 seems to working great. I'm listening now on 40m and the sensitivity seems excellent and the audio equally great. No hum because I now only need Local Gain knob around 4 instead of 9.
I will do a side-by-side comparison as before with my HF-380 but I am cautiously optimistic that R544 and R541 were the primary cause for my radio's "deafness". I will need to study the schematic more to fully understand this better.
There are some minor problems which I will first do some digging for information... my dial lock to adjust dial frequency moves the gear(s) but doesn’t lock them down. I'm sure the Y2K doc or other docs on the r390.net will help me repair that as well. I have a Collins R-390A that has been working well for years but the carrier meter no longer works and stays pegged to the right. Now I know where the carrier meter circuitry is located (at least on the R390) and I think I can work through that problem.
Many thanks to all that helped me keep my favorite receiver in the game.
Best
Jerry NY2KW (ex-K1JOS)
http://mailman.qth.net/mailman/listinfo/r-390 Administrator
-----Original Message-----
From: Jacques Fortin <jacques.f at videotron.ca>
Sent: Thursday, November 7, 2024 5:12 PM
To: k1jos at att.net
Cc: r-390 at mailman.qth.net
Subject: RE: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
Jerry, having a properly working NL will provide you a good audio output for sure, but that will not change the output you got from the diode loads line (the -7V) or the gain of the whole receiver.
I warn you about yesterday: those poor receivers can have been "abused" by many "golden screwdrivers" previous owners and a FULL checkup is in order !!
Plus the fact that they are 74 years old !
Call it a full restoration if you like...
That's what I done on mine and I never had to "chase" strange working problems thereafter.
Maybe I am lucky, I don't know...
73, Jacques, VE2JFE in Montreal
-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de k1jos at att.net Envoyé : 7 novembre 2024 16:54 À : 'Jim Whartenby' <old_radio at aol.com>; r-390 at mailman.qth.net Objet : Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
Thanks Jim, I weas looking at the wrong 470K (a 2W) but R544 is a small 1/4W mounted on one of the side phenolic boards. Just lifted one end and confirmed that is open. Will replace tonight, check voltages and resistances and hopefully that will be the reason for my low gain.
Jerry
-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On Behalf Of Jim Whartenby via R-390
Sent: Thursday, November 7, 2024 4:03 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
https://www.navsea.navy.mil/Portals/103/Documents/NSWC_Crane/SD-18/ResistorsFailure.pdf
Regards, Jim
Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy
On Thursday, November 7, 2024 at 02:14:25 PM CST, Jacques Fortin <jacques.f at videotron.ca> wrote:
Jerry, because R544 is still open... !
Is your +B checks at +180V ?
With the R544 in place (and good in value) you should measure about +40V on the cathodes, yes !
Do not ask why those hi-value resistors fail.
I have seen this many times, but nobody can tell why.
73, Jacques, VE2JFE in Montreal
-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de k1jos at att.net Envoyé : 7 novembre 2024 14:30 À : r-390 at mailman.qth.net Objet : Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
Before I replace R544, I wonder what caused it to fail. Checking voltages per manual, with Limiter at maximum 10, there should be 0 vdc at the plate (pin 6) or grid (7) or cathode (8) which I confirmed. However, with Limiter switched off there should only be 40vdc at the plate, grid and cathode and I find +155vdc. Does this make any sense?
Jerry
-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On Behalf Of k1jos at att.net
Sent: Thursday, November 7, 2024 2:08 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
I unplugged P117 from J517. All connections from P117-9 and P119-10 to Limiter switch are intact. There is no continuity from V507B-8 (cathode) to J517-9. I checked directly at the tube sockets; V507B cathode and V510 cathode are continuous as per schematic so that rules out issues at the tube sockets. It looks like it can only be R544... so now to remove the IF module.
More to follow............
Jerry
-----Original Message-----
From: Jacques Fortin <jacques.f at videotron.ca>
Sent: Thursday, November 7, 2024 12:10 PM
To: k1jos at att.net; 'Barry Scott' <72volkswagon at gmail.com>
Cc: r-390 at mailman.qth.net
Subject: RE: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
Jerry, looks like R544 is open, or just not there anymore !
73, Jacques, VE2JFE in Montreal
-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de k1jos at att.net Envoyé : 7 novembre 2024 10:46 À : 'Barry Scott' <72volkswagon at gmail.com> Cc : r-390 at mailman.qth.net Objet : Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
Hi Barry,
Could you do me a favor and also check resistance on V507B (Neg Peak Limiter) pin 8 cathode -- It should read 500k (Limiter knob at full CW) and 450k with Limiter switch OFF - I read an open circuit or resistance > 10Meg. The cathode of V507B is tied to the cathode of V510 (pin 3) which also reads open on my DMM.
Thanks in advance
Jerry
-----Original Message-----
From: Barry Scott <72volkswagon at gmail.com>
Sent: Wednesday, November 6, 2024 10:52 PM
To: k1jos at att.net
Cc: r-390 at mailman.qth.net
Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
I just checked resistance from V506 Pin 7 to ground in my R-390/URR and it checks a few ohms over 820 ohms.
Thanks,
Barry - N4BUQ
On Wed, Nov 6, 2024 at 8:38 PM Barry Scott <72volkswagon at gmail.com> wrote:
>
> That resistance measurement seems quite odd. R536 is supposed to be
> 820 ohms. Unless C523 is bad, I don't see how there should be
> anything much less than 820 ohms at pin 7 of V506 yet the resistance
> diagram shows 700 ohms. 99 ohms seems very wrong.
>
> Thanks,
> Barry - N4BUQ
>
> On Wed, Nov 6, 2024 at 8:12 PM <k1jos at att.net> wrote:
> >
> > Update....
> >
> > I checked voltages and resistances per TM 11-5820-357-35 (09 March 1962) for the IF amps V501 - V506. I don’t know if my R-390 had any mods, its SN 1256, but all the results were very close to the listed values except for V506, 6th IF amp. The cathode should read 700 ohms to ground and 8.2vdc and I find 99 ohms and 2.3vdc. The schematic shows the cathode bias resistor of 800 ohms and a 15ohm pot for carrier meter adjustment. There is a decoupling cap 0.1uF off the cathode that if leaky could bring the resistance down to my reading. But would this be enough to drop my gain so dramatically?
> >
> > Jerry
> >
> >
> > ______________________________________________________________
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