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

Tony Casorso canthony15 at msn.com
Sun Oct 21 16:01:11 EDT 2007 

Somebody just emailed me asking about KNUS. It is supposed to be on 710am. 
There is a "sister station" KBJD that simulcasts KNUS and goes by KNUS2. 
KBJD is at 1650 KHz and this is the one that I am havng issues with at the 
moment. I said KNUS because that's what I hear them saying at 3300KHz and at 
1650KHz. Interestingly (for me at least), it looks like KNUS2 is going to 
cease operations on Oct 29th. I don't know if KBJD is just changing hands or 
what.

Tony

----- Original Message ----- 
From: "Jon Schlegel" <ews265 at rochester.rr.com>
To: <r-390 at mailman.qth.net>
Sent: Sunday, October 21, 2007 1:45 PM
Subject: Re: [R-390] R-390a Image problem?


> Hmm,
>
> So then the only time you see distorted waveform out (plate) is when the 
> radio and hence the RF amp's plate load is tuned to 3300.  That all makes 
> sense
>
> I guess where I was going was a much lower than normal plate AC plate load 
> for the RF stage.  Failed something in Z201-1 or -02, C254 or further 
> downstream like the 1st Mixer.
>
> Need to think about this some more. should get back to you shortly.
>
> Jon
>
>
> At 01:19 PM 10/21/2007 -0600, you wrote:
>>Hi Jon,
>>
>>No, I mean using the signal generator I have sine in and not-so-sine out. 
>>I only use the KNUS signal for the spectrm analyzer because of the sig gen 
>>harmonics. On the scope, The sign gen distortion is not really visible. A 
>>little bit of asymmetry in the sine wave will give that second harmonic 
>>blip on the analyzer. In one cycle of the input sine wave, the plate 
>>signal goes up, comes down about half way, goes back up, comes fully down 
>>and back up to the starting point.
>>
>>I think this may be 'normal'. The plate circuit is tuned to 3.3 Mhz. When 
>>I hit it with the 1.65 Mhz signal it tries to ring at 3.3 Mhz. This 
>>combines with the 1.65 Mhz signal to produce the odd waveform I see.
>>
>>I'm not sure what to make of this. Either it's normal, or I'm not getting 
>>reasonable attenuation of the 1.65MHz signal through the antenna circuits 
>>(tuned to 3.3MHz), or the Q of the mixer input circuit is too high, or 
>>it's something else entirely.
>>
>>This is a good reason to have more than one receiver.
>>
>>Tony
>>
>>
>>----- Original Message ----- From: "Jon Schlegel" 
>><ews265 at rochester.rr.com>
>>To: <r-390 at mailman.qth.net>
>>Sent: Sunday, October 21, 2007 1:03 PM
>>Subject: Re: [R-390] R-390a Image problem?
>>
>>
>>>Gee.  DC readings look reasonable.  I see why now you're hesitant about 
>>>the generator.  Yup. forgot about that.
>>>
>>>So Tony, when you say sine in - grunge out, you're talking about the 
>>>KNUS's 1650 hHz signal as observed on the grid and plate of the RF amp. 
>>>Just making sure were in synch at this point.
>>>
>>>Here's a thought.  Watch your grid and plate signals on the scope and 
>>>yank the 1st Mixer, V202.
>>>
>>>Jon
>>>
>>>
>>>At 12:49 PM 10/21/2007 -0600, you wrote:
>>>>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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