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

Thu Nov 7 17:12:08 EST 2024

Yep...those should be 1/2 watt jobs...Those AB 470K 1/2w resistors have a 
tendency to drift up. I've found several that measure about 510K in the 390A 
AF decks but I don't bother with them as the decks work just fine.

73...Jordan VE6ZT

----- Original Message ----- 
From: "Jacques Fortin" <jacques.f at videotron.ca>
To: <k1jos at att.net>; <r-390 at mailman.qth.net>
Sent: Thursday, November 07, 2024 2:55 PM
Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?

> R544 is just a Allen Bradley 470K, 10% ½W resistor.
> The only Part List I know is in the first R-390/URR manual that you can 
> download here:
> https://www.royalsignals.org.uk/radio-rx-R390/2460.pdf
>
>
> 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 16:11
> À : 'Jacques Fortin' <jacques.f at videotron.ca>; r-390 at mailman.qth.net
> Objet : Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
>
> Fortunately, R544 is not under V510 where all the Amphenol Jack harness 
> wires but seems to be in the compartment just above.  Doesn’t look like 
> typical 2W CC but looks like much older style.  Will lift one end tonight 
> after dinner and see.  Where can I find the parts list with component 
> specifications.  I searched the TM 11-5820-357-35 manual.. Are they 
> submanuals also?
>
> Jerry
>
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On 
> Behalf Of Jacques Fortin
> Sent: Thursday, November 7, 2024 3:13 PM
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
>
> 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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