[R-390] Calibration Osc and 2nd Osc questions

[Thomas Hoyer]

Quick update from having a long day of "bonding time" with the radio yesterday.


Cal signal issue has been corrected. After much probing / measuring and head scratching turns out the 1st IF was not aligned correctly. Once I ran through the alignment of that stage the cal level is now good.


The low voltage I was measuring in the oscillator circuit was due to the use of a DVM. When I used my VTVM (Hickok 209A) the voltage measured correctly.


I did have a bad 14mc xtal - replaced and that circuit is working.


Went through a complete alignment and the radio now receives on all bands - some better then others, but we'll dig into that later. The next issue is that I have no AGC action and the S-meter works but only under very strong signals. So I have the IF chassis out and I'm working through those circuits.


Still having fun.......


Tom
W3TA



-----Original Message-----
From: bill.riches <bill.riches at verizon.net>
To: 'thoyer' <thoyer1 at verizon.net>; r-390 <r-390 at mailman.qth.net>
Cc: Bill Riches <bill.riches at verizon.net>
Sent: Sat, Dec 2, 2017 9:28 pm
Subject: RE: [R-390] Calibration Osc and 2nd Osc questions

Inside one of the cans on the rf deck there is a cap across the coil. I
think it is the below 8 mhz oscillator osc plate coil.  It changes value.  I
will look up the cap and coil numbers tomorrow when I am in the shop.  I
trust you have the manuals and know how to align the band switch.

Bill

-----Original Message-----
From: thoyer [mailto:thoyer1 at verizon.net] 
Sent: Saturday, December 2, 2017 7:56 PM
To: bill.riches at verizon.net; r-390 at mailman.qth.net
Subject: RE: [R-390] Calibration Osc and 2nd Osc questions

Hi Bill, 

I have not done a s/n check. A sensitivity check shows that it is not
performing up to snuff though. Instead of the 3-4 uV in the spec I'm seeing
closer to 10uV.

Right now I have the RF deck out chasing a 10mHz osc issue - looks like a
bad mica. I'm going to do some more checking on te RF deck before putting it
back in. I have a feeling there are a few more suspect caps lurking in
there........

Tom
W3TA 

-----Original Message-----
From: bill.riches at verizon.net [mailto:bill.riches at verizon.net]
Sent: Saturday, December 02, 2017 5:24 PM
To: 'thoyer'; r-390 at mailman.qth.net
Subject: RE: [R-390] Calibration Osc and 2nd Osc questions

Sensitivity below 8mhz might be down as it is a triple conversion set below
8 mhz and there are known sensitivity problems below 8 mhz.  Have you
checked actual rf s/n above 8 mhz and below 8 mhz. On the ones that restore
the average is around  .5 uv.

73,

Bill, WA2DVU

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of thoyer
Sent: Friday, December 1, 2017 7:35 PM
To: r-390 at mailman.qth.net
Subject: [R-390] Calibration Osc and 2nd Osc questions

After tinkering on my R-390A for a couple months, I now have it up and
running, but with a few bugs I'm steadily working out. The questions for
today are:

Why does the amplitude level of the calibration signal drop when I go below
8 mHz? Signals received on the AM broadcast band are nice and strong, but
the cal level is very low. I'll be digging into this issue this weekend so
I'm looking for some "been there, done that" advice. I have yet to probe
around the cal circuit, I'll start that tonight.

Also, the voltage called out for the grid on the 2nd oscillator is -10v - I
measure -.6v. Tube checks fine, a\lso swapped another in - no change.
Oscillator output seems reasonable 7 to 10 Vrms on most bands. I have a
couple bands with bad crystals (determined by substituting in a close in
freq crystal and the circuit producing output). The resistances around the
tube measure in spec. Maybe one of the caps is shot. Before I pulled the
chassis out, figured I'd pose the question here. Don't want to be chasing my
tail........

Overall the radio is coming back to life. Fun stuff..........

Tom
W3TA
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