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
<[email protected]> 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 : [email protected] <[email protected]> De la part
de [email protected] Envoyé : 7 novembre 2024 14:30 À : [email protected] 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: [email protected] <[email protected]> On Behalf
Of [email protected]
Sent: Thursday, November 7, 2024 2:08 PM
To: [email protected]
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 <[email protected]>
Sent: Thursday, November 7, 2024 12:10 PM
To: [email protected]; 'Barry Scott' <[email protected]>
Cc: [email protected]
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 : [email protected] <[email protected]> De la part
de [email protected] Envoyé : 7 novembre 2024 10:46 À : 'Barry Scott'
<[email protected]> Cc : [email protected] 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 <[email protected]>
Sent: Wednesday, November 6, 2024 10:52 PM
To: [email protected]
Cc: [email protected]
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 <[email protected]> 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 <[email protected]> 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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