[R-390] deaf below 8MHz (R-390A)

[Larry H]

Andre, Welcome to the r390 group.  I know that you will enjoy the R-390A.
Sounds like you've done some good things to it already.

The 1st mixer is not used above 8.0 mh, so is probably the 1st place to
look at.  A common problem is the switch segment S208 is not lined up
correctly, removing B+ to the 1st osc screen below 8 mh.  Another problem
is a bad contact on the crystal, it's housing, the osc tube or mixer tube.
And don't forget about the 1st var IFs, see if their  movement is working
correctly.  Have fun.

Regards, Larry

On Mon, May 20, 2019 at 3:52 AM atfu <atfu at gmx.de> wrote:

>
> Dear All,
>
> I am the proud owner of a recently bought R-390A (Capehart) with an
> excellent history: From late 60s to early 90s in the labs of the German
> Aviation and Space Agency (with regular servicing); thereafter taken
> home by one of the employees. I bought the RX from the estate of that
> employee, so couldn't put any questions to the former owner. Compared to
> other radios I saw, this one is of an exceptionally sound and clean
> appearance, in and out.
>
> When taken to my shack it came well to life on all bands, though,
> perhaps, not up to the legendary sensitivity that it is capable of in
> principle. (Carrier meter was definitely reacting low: about 20 dB on
> strong cal signal, even lower on strong signals from ANT.)
>
> First steps taken: Clean all contacts and retire paper caps in AF and IF
> as a preventive measure. First AF. All went well and the result was an
> audible improvement. (BTW all caps I found, mostly yellow Aerovox, were
> within specs on my LC-meter.)  Calibration signal and reception on all
> bands. (Still low carrier meter.)
>
> Next IF.  Replaced all but C533, C536 (both under BFO shaft), C549 (a
> bit tough), and C551 (in alloy cap). Checked and re-checked and
> re-checked for proper values and connections -- ok. (I did this one by
> one so as to rule out connection errors.) Result was a definite
> improvement on all bands above and including 8 MHz, below that -- NIL,
> including no cal signal. Carrier meter appears pretty dead now, also on
> the upper bands.
>
> So troubleshooting is called for. I started with the flow chart from the
> Cryotology Class and procedures according to the Y2K manual.
>
> 1. Although I didn't mess with the mechanics, I first checked the
> mechanical alignment (according to Y2K). All fine. V207/Pin 6 to
> J208/Pin D gave 56K: so I suppose no field change 7 was made and the
> value is thus spot on for R210.
>
> 2. V202, V207, V201 warm up. I don't have equipment to check them beyond
> that though.
>
> So here is my question: How should I proceed from here? In particular,
> what may impede the cal signal to be heard below 8 MHz?
>
> My test equipment includes a working AN/URM-25(H) (hooked up to a modern
> freq counter), but no tubes tester.
>
> Hope someone may be able to help!
>
> Vy 73! Andre, DM1AA
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>