[R-390] R-390a Image problem?
Tony Casorso
canthony15 at msn.com
Sun Oct 21 14:49:26 EDT 2007
Hi Jon,
Actually, the signal generator has a fair amount of second harmonic in it so
the radio station is cleaner on the spectrum analyzer.
I did switch to the signal generator and the scope and I can see the
distortion plain as day. Sine wave in, distorted out.
Voltages are
With no AGC applied:
Plate 201v
screen 178v
cathode 2.1v
grid -.5v
With AGC applied:
Plate 215v
screen 201v
cathode .22v
grid -4.2v
These was taken with a signal from the signal generator applied.
Tony
----- Original Message -----
From: "Jon Schlegel" <ews265 at rochester.rr.com>
To: <r-390 at mailman.qth.net>
Sent: Sunday, October 21, 2007 12:26 PM
Subject: Re: [R-390] R-390a Image problem?
> Tony,
>
> What are stage DC voltages doing?
>
> Also, can you reproduce the behavior with the sig gen at the input instead
> of KNUS's megavolt/meter signal. If so, conditions would be more
> controllable. You could easily see behavior over level change, etc.
>
> Jon
>
>
> At 12:11 PM 10/21/2007 -0600, you wrote:
>>Hi all,
>>
>>I looked at it with the spectrum analyzer this morning and I did not see
>>any oscillation. What I did see is that I have over 100Mv of signal from
>>the KNUS broadcast station at the balanced antenna terminals. It is
>>reduced to about a quarter of that by the antenna circuits (tuned to
>>3.3Mhz) so 20+ millivolts is going into the RF amplifier. There is no
>>visible signal at the second harmonic (3.3 Mhz) going into the RF stage.
>>At the grid of the first mixer with the receiver tuned to 3.3Mhz, the
>>broadcast band signals including the huge KNUS signal are gone (below the
>>floor of my spectrum analyzer) but there is about a 1 millivolt signal at
>>3.3Mhz. It would appear that some kind of non-linearity in the RF stage is
>>creating a strong second harmonic in the RF stage.
>>
>>Tony
>>
>>
>>----- Original Message ----- From: "DW Holtman" <tubestuff at comcast.net>
>>To: "Bob Camp" <ham at cq.nu>; "Tony Casorso" <canthony15 at msn.com>
>>Cc: <r-390 at mailman.qth.net>
>>Sent: Saturday, October 20, 2007 6:28 PM
>>Subject: Re: [R-390] R-390a Image problem?
>>
>>
>>>Hello,
>>>
>>>I also have a 50KW broadcast station in my area. It causes problems on
>>>both of my R-390A's, 51S-1 and R-392. The cross over distortion is mostly
>>>heard in the broadcast bands. I built a highpass filter with about a 3MHZ
>>>roll off. Put it in series with the antenna lead, going into the
>>>multicoupler and it works great. Ended the problem, can still receive
>>>broadcast bands with the filter inline because they are so strong.
>>>
>>>Best,
>>>DW Holtman
>>>WB7SSN
>>>
>>>----- 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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>>>>>>
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