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

Barry n4buq at knology.net
Thu Nov 7 11:36:19 EST 2024


Hi Jerry,

No problem.  I'm measuring an R-390/URR.

BTW, I just checked and both R544 and R125 in mine are 10% over spec.  Not too bad and I don't really use the limiter much at all so not too worried about it for now.  A LOT of the resistors in mine are on the edge or over spec.  Not surprising for CC resistors that old.

Thanks,
Barry - N4BUQ

> Ooops please I see that J517 plugs into P117.  Yes and removed and reinserted a
> few times with no change
> -----Original Message-----
> From: k1jos at att.net <k1jos at att.net>
> Sent: Thursday, November 7, 2024 11:28 AM
> To: 'Barry' <n4buq at knology.net>
> Cc: 'Barry Scott' <72volkswagon at gmail.com>; 'R-390 Mailing List'
> <r-390 at mailman.qth.net>
> Subject: RE: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
> 
> Hi Barry,
> 
> Do you mean J517, the large multiwire amphenol?  Arte you measuring a R390 or
> 390A?
> 
> Jerry
> 
> -----Original Message-----
> From: Barry <n4buq at knology.net>
> Sent: Thursday, November 7, 2024 11:03 AM
> To: k1jos <k1jos at att.net>
> Cc: Barry Scott <72volkswagon at gmail.com>; R-390 Mailing List
> <r-390 at mailman.qth.net>
> Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
> 
> 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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