[R-390] TR: R-390 Woes

[Jacques Fortin]

Hi Adam,

I think I recognise this mod., the clue being the 56k resistor in the
picture(s).

See attached doc.

If it is really the original W3JHR mod. that was implemented there, the BFO
on/off switch has been also changed for a DPDT version (switching the audio
input between the AM and product detectors and powering the BFO oscillator
at the same time).

If it is that, the BFO tube (V508) have to be a 6BE6/5750 instead of a
6BA6/5749


This is basically the same product detector that I use in my own R-390 and
R-390As, by using a changeover relay inside the IF deck instead of using a
substitute BFO switch.

See also the W7DI type of implementation attached.

Larry Haney also worked around this theme and used a 6BY6 tube for the
product detector because it works better than a 6BE6 in the same
configuration.

I also worked with Larry to find a way to still use the noise limiter in the
SSB mode, but the result of our experiments are not final, and the AGC
modifications we devised to “improve” the R-390 / 390A are still not fully
tested.

Stay tuned, I should have time to re-visit that during the next winter.

 

73, Jacques, VE2JFE in Montreal

 

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <mailto:r-390-bounces at mailman.qth.net>
<r-390-bounces at mailman.qth.net <mailto:r-390-bounces at mailman.qth.net> > De
la part de Adam Morehouse
Envoyé : 8 octobre 2025 03:44
À : R-390 Mailing List <r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net>
>
Objet : Re: [R-390] R-390 Woes

 

I might have found the issue.

 

Can anyone tell me if the white coax in the follow pictures is supposed to
be there?

 

 <https://photos.app.goo.gl/M6Qcr9mXFrZ6sgiRA>
https://photos.app.goo.gl/M6Qcr9mXFrZ6sgiRA

 

It doesn't look original to me, nor does the the resistors and caps in front
of the BFO. They seem to be hooked to V508 and RT512.

 

 

 

 

On Tue, Oct 7, 2025, 16:55 Adam Morehouse < <mailto:morehouse90 at gmail.com>
morehouse90 at gmail.com> wrote:

 

> Hey guys,

> 

> I appreciate the pointers on my R-392, and now that it's buttoned up, 

> it's time to work on my R-390. I only tested this briefly when I first 

> got it, today I threw it up on the bench. Supposedly this was restored 

> by Rick Mish, it is very clean (except the gear train, which has a lot 

> of fresh grease...), and the front panel is pristine.

> 

> It does pull stations, but the volume is extremely low in AGC mode, 

> and gets slightly louder when placed into MGC.

> 

> In MGC, with the BFO switched on, it plays at a normal (not super 

> loud, but loud) volume.

> In AGC, with the BFO switched on, it hums, low volume audio.

> 

> The limiter seems to have no effect, and varying the BFO doesn't do 

> anything at all no matter AGC/MGC.

> 

> I have Tom's solid state kit installed, and B+ at the AF deck test 

> point is a steady 180.5vdc.

> 

> I am going to dig out the TM's later on, I have them somewhere...but 

> maybe somebody here can help point me in the right direction.

> 

> Thanks!

> 

> Adam K2AAM

> 

> 

> 

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