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

[Barry]

Hi Jerry,

OFF: 520k
CW: 583k
CCW: 638k

Those don't exactly meet the specs.  I probably have more than one drifted resistor that I need to address at some point.

So strange that so many of those readings are so far off in your radio.  It's almost as if another connector is loose or making poor connections.  I presume you've reseated P117?

Hope that helps,
Barry - N4BUQ

> 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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