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

Jon Schlegel ews265 at rochester.rr.com
Sun Oct 21 15:45:28 EDT 2007 

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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