[R-390] R-390a Image problem?

[Bob Camp]

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
>>>>>>> _____________________________________________________________
>>>>>>> R-390 mailing list
>>>>>>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>>>>>>> Help: http://mailman.qth.net/faq.htm
>>>>>>> Post: mailto:R-390 at mailman.qth.net
>>>>>>> Unsubscribe: http://mailman.qth.net/mailman/options/r-390
>>>>>>>
>>>>>
>>>
>