[R-390] R-390a Image problem?
Tony Casorso
canthony15 at msn.com
Sat Oct 20 19:03:08 EDT 2007
Hi Bob,
That has occurred to me. The only thing is that none of my other radios do
this on the same antenna, including my R-392. Plus, the signal strength is
40db on the meter. I didn't expect the R-390a to be weak in this area.
Tony
----- Original Message -----
From: "Bob Camp" <ham at cq.nu>
To: "Tony Casorso" <canthony15 at msn.com>
Cc: <r-390 at mailman.qth.net>
Sent: Saturday, October 20, 2007 4:21 PM
Subject: Re: [R-390] R-390a Image problem?
> Hi
>
> By any chance are we chasing a ghost here?
>
> I used to have a 50KW AM station a stones throw away from my back yard.
> My long wire could get a reading on a Bird Termline with a good matchbox
> in between. It was always amazing to me just how different radios would
> and would not pick up which harmonics of that station.
>
> See if you can get a signal generator you trust. Check the radio and see
> what it's really doing. If the front end of the radio is running ok, and
> it's properly aligned, there may not be anything wrong with the radio.
>
> Bob
>
> On Oct 20, 2007, at 1:13 PM, Tony Casorso wrote:
>
>> I just finished checking the injection level at the first mixer. It
>> seems more than adequate at 1 volt rms but I don't really know what is
>> supposed to be. First mixer cathode is at about 8.5 volts (manual says
>> 9.7).
>>
>> I have a spectrum analyzer over in the corner. I might be able to use it
>> to look for oscillations in the RF stage. Maybe I'll have time later
>> today.
>>
>> Tony
>>
>>
>>
>> ----- Original Message ----- From: "Jon Schlegel"
>> <ews265 at rochester.rr.com>
>> To: <r-390 at mailman.qth.net>
>> Sent: Saturday, October 20, 2007 10:55 AM
>> Subject: Re: [R-390] R-390a Image problem?
>>
>>
>>> Tony,
>>>
>>> Some further thoughts. Again, I'm not really familiar with the 390 yet
>>> so these are just some general ideas.
>>>
>>> Could the screen or suppressor/cathode of the RF amp be lifting off of
>>> RF ground (bad C229, C227?). This could cause some instability.
>>> Another possibility along these lines is a problem with the parasitic
>>> suppressor, E212, or something downstream from it. E212's presence in
>>> the design is tip off that the stage could be *hot*. If the stage is
>>> oscillating at some frequency that's not immediately obvious (VHF
>>> range?), a non-linearity could be created that might generate the 2nd
>>> harmonic of 1650 kHz that you are seeing. You could try to *sniff* the
>>> existence of an oscillation using other receiver(s) you may have on
>>> hand. Use a short wire probe as the search receiver's antenna, put it
>>> next to the RF tube and start searching for any signs of life.
>>>
>>> Regards,
>>> Jon
>>>
>>>
>>>
>>> At 09:42 PM 10/19/2007 -0600, you wrote:
>>>> Checking the injection levels is a good idea. I'll try that tomorrow.
>>>>
>>>> Tony
>>>>
>>>>
>>>>> From: Bob Camp <ham at cq.nu>
>>>>> To: Tony Casorso <canthony15 at msn.com>
>>>>> CC: <R-390 at mailman.qth.net>
>>>>> Subject: Re: [R-390] R-390a Image problem?
>>>>> Date: Fri, 19 Oct 2007 23:06:32 -0400
>>>>>
>>>>> Hi
>>>>>
>>>>> Stage voltages are a good idea if you have a VTVM. With an RF probe
>>>>> you can also check the injection levels at the mixers. Low drive to a
>>>>> mixer can cause all sorts of odd things. Your 17 MHz crystal
>>>>> oscillator may be a bit "sick" for instance ....
>>>>>
>>>>> Another stupid thing to check - did somebody put a couple of diodes
>>>>> up in the antenna relay to "overload protect" the radio?
>>>>>
>>>>> Bob
>>>>>
>>>>>
>>>>> On Oct 19, 2007, at 10:48 PM, Tony Casorso wrote:
>>>>>
>>>>>> I see what you mean about AGC. I checked it anyway. -11 volts on a
>>>>>> strong local station. I swapped tubes with no improvement. I wonder
>>>>>> if the stage bias could be wrong? I guess I should measure the
>>>>>> voltages just to be sure.
>>>>>>
>>>>>> When I said 1st RF stage, I guess I forgot this was an R-390a. Part
>>>>>> of the cost reduction removed one of the RF stages didn't it? There
>>>>>> is only one.
>>>>>>
>>>>>> The antenna is a 100 foot longwire.
>>>>>>
>>>>>> Tony
>>>>>>
>>>>>>
>>>>>> ----- Original Message ----- From: "Bob Camp" <ham at cq.nu>
>>>>>> To: "Tony Casorso" <canthony15 at msn.com>
>>>>>> Cc: <R-390 at mailman.qth.net>
>>>>>> Sent: Friday, October 19, 2007 8:36 PM
>>>>>> Subject: Re: [R-390] R-390a Image problem?
>>>>>>
>>>>>>
>>>>>>> Hi
>>>>>>>
>>>>>>> I'd swap it for another tube just in case.
>>>>>>>
>>>>>>> With no input to the radio, there should be pretty much no AGC to
>>>>>>> the front end. It may be the problem, but only indirectly.
>>>>>>>
>>>>>>> If the radio is fine with no front end tube, you probably have one
>>>>>>> very large antenna.....
>>>>>>>
>>>>>>> Bob
>>>>>>>
>>>>>>>
>>>>>>> On Oct 19, 2007, at 10:17 PM, Tony Casorso wrote:
>>>>>>>
>>>>>>>> Aha! The 1st RF tube is correct (6DC6) but when I remove the tube
>>>>>>>> and put a small cap from pin1 to pin 5 (grid to plate), the
>>>>>>>> receiver works fine and NO image. I'm going to check the AGC to
>>>>>>>> that stage.
>>>>>>>>
>>>>>>>> Tony
>>>>>>>> ----- Original Message ----- From: "Bob Camp" <ham at cq.nu>
>>>>>>>> To: "Tony Casorso" <canthony15 at msn.com>
>>>>>>>> Cc: <R-390 at mailman.qth.net>
>>>>>>>> Sent: Friday, October 19, 2007 7:13 PM
>>>>>>>> Subject: Re: [R-390] R-390a Image problem?
>>>>>>>>
>>>>>>>>
>>>>>>>>> Hi
>>>>>>>>>
>>>>>>>>> I'd check the grounds as Jon suggested. The R390 can pick up
>>>>>>>>> "stuff" from the power line pretty easily. The AC line filter
>>>>>>>>> works both ways with a loose ground ...
>>>>>>>>>
>>>>>>>>> Next up would be to start swapping front end tubes. You may find
>>>>>>>>> that you simply have a defective tube. You may also find that
>>>>>>>>> somebody "improved" the design by putting in a tube that didn't
>>>>>>>>> belong there.
>>>>>>>>>
>>>>>>>>> Bob
>>>>>>>>>
>>>>>>>>> On Oct 19, 2007, at 8:58 PM, Tony Casorso wrote:
>>>>>>>>>
>>>>>>>>>> Hi Bob, I'm using the balanced input. I bought a twinax to BNC
>>>>>>>>>> adapter so one side of the balanced input is grounded.
>>>>>>>>>>
>>>>>>>>>> Same antenna doesn't bother the R-392.
>>>>>>>>>>
>>>>>>>>>> Tony
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> ----- Original Message ----- From: "Bob Camp" <ham at cq.nu>
>>>>>>>>>> To: "Tony Casorso" <canthony15 at msn.com>
>>>>>>>>>> Cc: <R-390 at mailman.qth.net>
>>>>>>>>>> Sent: Friday, October 19, 2007 6:52 PM
>>>>>>>>>> Subject: Re: [R-390] R-390a Image problem?
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> Hi
>>>>>>>>>>>
>>>>>>>>>>> Which antenna input are you running into? The situation you
>>>>>>>>>>> describe would be pretty typical if you run a long antenna
>>>>>>>>>>> into
>>>>>>>>>>> the "unbalanced" input.
>>>>>>>>>>>
>>>>>>>>>>> Bob
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> On Oct 19, 2007, at 8:31 PM, Tony Casorso wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Hi everyone. This is my first post to the list although I've
>>>>>>>>>>>> been following it for a long time now. A few months back I
>>>>>>>>>>>> bought a 67 EAC R-390a. The only problem I had was an open
>>>>>>>>>>>> Z-503 AGC coil. I replaced that and did an alignment and the
>>>>>>>>>>>> radio seemed to be working real well. Sensitivity was very
>>>>>>>>>>>> good on all bands.
>>>>>>>>>>>> Recently I've noticed broadcast stations coming through in
>>>>>>>>>>>> the
>>>>>>>>>>>> 3Mhz band. A local station on 1650KHz is about 40db at
>>>>>>>>>>>> 3300KHz on the R-390a. I don't hear it on my R-392. Even
>>>>>>>>>>>> moving the 2-4MHz RF slug rack by hand, I still hear the
>>>>>>>>>>>> station (although it does get a bit quieter). There are
>>>>>>>>>>>> several other stations coming through as well on other
>>>>>>>>>>>> frequencies. I didn't notice anything odd when I aligned it,
>>>>>>>>>>>> everything seemed to peak like it should.
>>>>>>>>>>>> Looking around at other frequencies with my signal generator,
>>>>>>>>>>>> I started noticing all kinds of harmonic responses, but
>>>>>>>>>>>> that is probably (at least to some degree) just my signal
>>>>>>>>>>>> generator (a Boonton 102C). I'm pretty sure something is
>>>>>>>>>>>> wrong here but I'm
>>>>>>>>>>>> scratching my head trying to think of a good explanation. If
>>>>>>>>>>>> the BC station harmonic was that bad, I'd hear it in my
>>>>>>>>>>>> other radios I would think.
>>>>>>>>>>>>
>>>>>>>>>>>> Ideas anyone? How do I track this one down?
>>>>>>>>>>>>
>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>
>>>>>>>>>>>> Tony
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