[R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?

[k1jos at att.net]

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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