[R-390] W0BT and N6PY mods in ER Magazine

[Renée Deeter]

good evening all, nice to be back.....
I just finished doing the W0BT  mod  in my  R725.  wonderful, thanks  to 
N6PY for the diodes so there are no wiring changes! Tnx to both it works 
better than my  AGC mod! ....I'll give the prod det a shot in a 
390A....already running dual triode prod det in my 725 with a similar 
switching scheme.
so folks the answer is it should works in a 390! probably need to change 
the TB102 values for the front end.
73
Renée,  K6FSB


Masters Andy wrote:
> Good evening list.  Recently, I decided to modify my
> R-390A based on the September 2006 issue of ER
> magazine. 
>
> I made the following mods:
>
> 1. N6PY's noise limiter circuit. Result-it does work
> more effectively with less apparent distortion when
> the limiter is turned on.  It also works nicely when
> the BFO is turned on.
>
> 2. N6PY's detector mod.  This was a bit more
> challenging but well worth the effort. SSB sounds
> fabulous now on the receiver. I initially ended up
> with increased distortion on AM but, based on the
> advice of Ray, N0DMS, I changed out the disc .01 cap I
> was using as C2A to a mylar and then changed its value
> to .022 which worked better for me-passing more low
> end audio.  The distortion went away.  
>
> 3. W0BT AGC mod. A big step but also well worth the
> effort.  My R-390A came to me already with the Rick
> Mish SSB AGC Mod on the back terminals and the
> Langford AGC mod.  Removing the Mish mod was no big
> deal but moving from an undocumented Lankford mod to
> the new circuit was tedious.  There is a typo on page
> 32, item 6 (should always read .1uf) but the article
> is very easy to follow and mine worked the first time.
>
> I did have a few questions about the alignment
> procedure but Clark and Ray wrote the procedure out
> correctly and my issues were a short between the
> headsets...
>
> In aligning my unit, I used my TEK 2465A scope to
> monitor the IF output waveform and the audio out
> waveform at the speaker while using a RMS Voltmeter to
> measure the line output on the top side of the line
> out pot.  I looked for symmetry in the modulated
> signal and tuned T503 and Z503 as suggested in the
> article. It does make a difference. 
>
> I made a serious mistake of trying to tweak T501 and
> T502 on my IF board.  My slugs on these two
> transformers are tight and when I applied lug nut
> torque to T501, I promptly twisted the coil form right
> around ripping the transformer wires right off the
> vertical wires that hold the caps and resistors in
> place on the coil forms.  If you have never resoldered
> those thin wires-it is no fun.
>
> Over all result is a much better AGC system, a noise
> limiter that functions better, and a nice SSB product
> detector that sounds really good.
>
> I have also discovered some issues in my audio amp (a
> Kleronomos mod audio amp).  I can see nice flat
> waveform on the IF from about 40hz through 6+Khz on
> the IF with my signal generator and using the 8 or 16
> khz IF filters, but the audio is only flat from about
> 80hz through basically 3Khz and then it rolls off
> through 6+khz passing audio out to about 10 Khz.  The
> issue seems to be in the audio amp but I don't know
> where yet.
>
> All of this to say if your thinking about doing these
> mods, they do work.
>
> Dutch Masters NU5O
>
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