I've got a National NC-46 that I'm resurrecting. The alignment is waaay out
of wack, with the top ends of the tuning ranges as much as 25% higher in
frequency than they should be. Furthermore, when I increase the trimmer
caps on the RF coils the resonant frequency appears to go _up_ instead of
down (I even tacked on a fixed capacitance to verify my sanity). I've owned
and maintained newer tube radios, and built transistor rigs, so in theory I
should know what I'm doing, but this problem has me stumped.

Does any of this sound familiar? Are there any factory manuals available
for the NC-46 that detail the factory's opinion of the correct alignment
procedure? Where can I get one?

Thanks in advance.

-------------------------------------------
Tim Wescott, KG7LI

Tim Wescott wrote:

Does any of this sound familiar? Are there any factory manuals available
for the NC-46 that detail the factory's opinion of the correct alignment
procedure? Where can I get one?

Thanks in advance.

-------------------------------------------
Tim Wescott, KG7LI

Download at
http://bama.sbc.edu/national.htm

-Bill

Tim Wescott wrote:

I've got a National NC-46 that I'm resurrecting. The alignment is waaay out
of wack, with the top ends of the tuning ranges as much as 25% higher in
frequency than they should be.


You probably know this already, but it bears repeating:
Alignment is never waaay out of whack - unless someone with
a "golden screwdriver" was in there before you. Look for
a defective component in the circuit - open/shorted/changed
value caps come to mind.

wrote in message ...
Tim Wescott wrote:

I've got a National NC-46 that I'm resurrecting. The alignment is waaay out
of wack, with the top ends of the tuning ranges as much as 25% higher in
frequency than they should be.


You probably know this already, but it bears repeating:
Alignment is never waaay out of whack - unless someone with
a "golden screwdriver" was in there before you. Look for
a defective component in the circuit - open/shorted/changed
value caps come to mind.

Sometimes the alignment is not correct in the factory manual ,try the
reverse ,set top of band with slug and bottom with cap,if that doesn`t
work---set top with cap and bottom with slug,,also if you have
bandspred make sure the var cap in min position,(out) position..make
sure youhave an accurate sig source..GL Harold W4PQW

You probably know this already, but it bears repeating:
Alignment is never waaay out of whack - unless someone with
a "golden screwdriver" was in there before you. Look for
a defective component in the circuit - open/shorted/changed
value caps come to mind.

The rig has obviously been worked on -- it had a silicon diode on the
rectifier, a new power supply cap of unknown vintage, and no glass in the
window. I originally suspected a golden screwdriver type because of that,
but the problem now is that it just _won't_ go where it's supposed to.

I was hoping that the symptom (the coils tune the _wrong_ direction with
capacity change) would ring a bell for someone; it looks like I'll actually
have to dig in and engage my brain on this problem.

Thanks

Tim Wescott wrote:
You probably know this already, but it bears repeating:
Alignment is never waaay out of whack - unless someone with
a "golden screwdriver" was in there before you. Look for
a defective component in the circuit - open/shorted/changed
value caps come to mind.


The rig has obviously been worked on -- it had a silicon diode on the
rectifier, a new power supply cap of unknown vintage, and no glass in the
window. I originally suspected a golden screwdriver type because of that,
but the problem now is that it just _won't_ go where it's supposed to.

I was hoping that the symptom (the coils tune the _wrong_ direction with
capacity change) would ring a bell for someone; it looks like I'll actually
have to dig in and engage my brain on this problem.

Thanks


Could this be a case of low-side versus high-side LO injection?

-Bill

"- - Bill - -" exray@coquidotnet wrote in message
...
Tim Wescott wrote:
-- snip --
I was hoping that the symptom (the coils tune the _wrong_ direction with
capacity change) would ring a bell for someone; it looks like I'll
actually
have to dig in and engage my brain on this problem.

Thanks


Could this be a case of low-side versus high-side LO injection?

-Bill


I wish it were, but its in the input circuit -- when the dial (in band 'C')
reads 3MHz the coil tunes at 4.5MHz, as verified both with a grid-dip
oscillator and with a signal generator/scope. At the low end of the range
it's not so bad.

Tim Wescott wrote:


I wish it were, but its in the input circuit -- when the dial (in band 'C')
reads 3MHz the coil tunes at 4.5MHz, as verified both with a grid-dip
oscillator and with a signal generator/scope. At the low end of the range
it's not so bad.


I just looked at the schematic...I gather that there is a "T1" for each
band although only one is shown?
Is it just that one band or do all of them misbehave?

-Bill

"- - Bill - -" exray@coquidotnet wrote in message
...
Tim Wescott wrote:


I wish it were, but its in the input circuit -- when the dial (in band
'C')
reads 3MHz the coil tunes at 4.5MHz, as verified both with a grid-dip
oscillator and with a signal generator/scope. At the low end of the
range
it's not so bad.


I just looked at the schematic...I gather that there is a "T1" for each
band although only one is shown?
Is it just that one band or do all of them misbehave?

-Bill


Yes, that's the arrangement -- I've checked the two lower bands ("D" and
"C") and they both have the problem. The other two don't, which is odd --
you'd expect the problems to be worse at the high-frequency end.

Tim Wescott wrote:


Yes, that's the arrangement -- I've checked the two lower bands ("D" and
"C") and they both have the problem. The other two don't, which is odd --
you'd expect the problems to be worse at the high-frequency end.


Hmmm...shorted turns comes to mind since those coils would have the most
turns. Whithout doing any major surgery could you try to add a few
turns as an experiment to see what the result might be?
Another guess might be moisture having impregnated the coil forms.
Often a good DVM can read a leakage resistance right across the cardboard.
Do you have the correct 6K8 in place (glass vs metal)

-BM