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

[Tony Casorso]

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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>>
>