Hello,

Got this radio in a hamfest. Now in the process of restoring. Replaced all tubes, filter caps, all other tubular caps and line cord. Rewired line cord so that the switch is in the hot side of the line. Repainted the cabinet. The radio played fairly OK when I got and plays the same now.

The problem is that there is a high pitched squeal when tuning the radio from station to station. When a strong station is tuned in, the noise is gone. If a weak station is tuned in, the squeal is still there but lower in intensity and very annoying. The noise was present when I got the radio; nothing that I have done has corrected the problem of affected it in any way.

Any ideas as to what this is and what I can do to correct it?

Thanks in advance,
Noel

Sounds like it needs an IF alignment. Also clean the CW AM switch.

:Hello,
:
:Got this radio in a hamfest. Now in the process of restoring. Replaced all tubes, filter caps, all other tubular caps and line cord. Rewired line cord so that the switch is in the hot side of the line. Repainted the cabinet. The radio played fairly OK when I got and plays the same now.
:
:The problem is that there is a high pitched squeal when tuning the radio from station to station. When a strong station is tuned in, the noise is gone. If a weak station is tuned in, the squeal is still there but lower in intensity and very annoying. The noise was present when I got the radio; nothing that I have done has corrected the problem of affected it in any way.
:
:Any ideas as to what this is and what I can do to correct it?
:
:Thanks in advance,
:Noel

I had a similar problem once. The squeal was dependent on the signal strength which controlled the AVC, and the gain of the IF amp. I finally found it was an oscillating IF strip. A couple of little caps in the AVC line were defective. New caps fixed the problem.
When the station was weak and the IF was high gain, the thing oscillated through the AVC bus. Shorting the AVC to ground should prove this.
Lewis

::Hello,
::
::Got this radio in a hamfest. Now in the process of restoring. Replaced all tubes, filter caps, all other tubular caps and line cord. Rewired line cord so that the switch is in the hot side of the line. Repainted the cabinet. The radio played fairly OK when I got and plays the same now.
::
::The problem is that there is a high pitched squeal when tuning the radio from station to station. When a strong station is tuned in, the noise is gone. If a weak station is tuned in, the squeal is still there but lower in intensity and very annoying. The noise was present when I got the radio; nothing that I have done has corrected the problem of affected it in any way.
::
::Any ideas as to what this is and what I can do to correct it?
::
::Thanks in advance,
::Noel
:
:
:I had a similar problem once. The squeal was dependent on the signal strength which controlled the AVC, and the gain of the IF amp. I finally found it was an oscillating IF strip. A couple of little caps in the AVC line were defective. New caps fixed the problem.
:When the station was weak and the IF was high gain, the thing oscillated through the AVC bus. Shorting the AVC to ground should prove this.
:Lewis
:
I agree with Lewis. If you decrease the RF gain, does the squeal disappear?
I had a squealer NC-98 like this and by 'detuning' the 2nd IF slightly, the squeal would stop. During the oscillation my AVC was something like -22 volts and the S-meter would almost peg.
I never actively set out to collect Nationals, but now find myself with a few of them. I have a scanned owners manual for the NC-60 Special if you would provide your e-mail I will send it.
There is a National forum on the QTH.net website. It is free to join and has good folks there.
:

:::Hello,
:::
:::Got this radio in a hamfest. Now in the process of restoring. Replaced all tubes, filter caps, all other tubular caps and line cord. Rewired line cord so that the switch is in the hot side of the line. Repainted the cabinet. The radio played fairly OK when I got and plays the same now.
:::
:::The problem is that there is a high pitched squeal when tuning the radio from station to station. When a strong station is tuned in, the noise is gone. If a weak station is tuned in, the squeal is still there but lower in intensity and very annoying. The noise was present when I got the radio; nothing that I have done has corrected the problem of affected it in any way.
:::
:::Any ideas as to what this is and what I can do to correct it?
:::
:::Thanks in advance,
:::Noel
::
::
::I had a similar problem once. The squeal was dependent on the signal strength which controlled the AVC, and the gain of the IF amp. I finally found it was an oscillating IF strip. A couple of little caps in the AVC line were defective. New caps fixed the problem.
::When the station was weak and the IF was high gain, the thing oscillated through the AVC bus. Shorting the AVC to ground should prove this.
::Lewis
::
: I agree with Lewis. If you decrease the RF gain, does the squeal disappear?
: I had a squealer NC-98 like this and by 'detuning' the 2nd IF slightly, the squeal would stop. During the oscillation my AVC was something like -22 volts and the S-meter would almost peg.
: I never actively set out to collect Nationals, but now find myself with a few of them. I have a scanned owners manual for the NC-60 Special if you would provide your e-mail I will send it.
: There is a National forum on the QTH.net website. It is free to join and has good folks there.
::
:
:Hello all,

Thanks for the ideas. Spraying the volume control with cleaner seemed to help a bit. Surprised at myself for not doing this sooner. The squealing is still there but not as bad.

I was now able to "tune around" which allowed me to notice another issue which may be related to the original squealing problem.

Switching to CW (40M) the squealing is completely gone when tuning from one station to another. However, the volume is very low. Switching back to AM the "CW thumps" are nice and loud. A;so, switching the antenna from a 10' wire on the floor to a dipole 50' up increases the volume as you would expect.

However, when tuning an AM station (on AM), switching between the wire and dipole really produces little or no change in volume. I'm wondering at this point if the problem is something in the AVC line and/or IF strip.

The NC60 does not have an RF gain control or S-meter.

I have the manual but no test equipment other than a Simpson 260.

1. Detune the IF, can I realistically do this by "ear" and make small incremental adjustments (1/4 turn, then another, etc.)? Adjust 1st or 2nd or both?
2. AVC line, there are 3 caps associated with the volume control: 1x (0.01uf) attached to the wiper terminal and the other 2x (100uuf) roughly in parallel with terminals 2 & 3. - are these the caps you mean? The cap from the plate of the Det/Amp 12AV6 to grid of the Audio/Out 50C5 (0.01uf) I already replaced.

Thanks,
Noel

Would think tuning the IF correctly first would give the best results. A 1/4 turn on any of the IF trimmers is really a lot. It would be just a slight turn less than 1/8. If you don't have a signal generator, post your E-Mail address. I can send you a procedure for Aligning Without Instruments. After doing this the performance should be improved.

:Would think tuning the IF correctly first would give the best results. A 1/4 turn on any of the IF trimmers is really a lot. It would be just a slight turn less than 1/8. If you don't have a signal generator, post your E-Mail address. I can send you a procedure for Aligning Without Instruments. After doing this the performance should be improved.
:
Thank you Warren.
Please send to nlukens1@comcast.net

Noel

::Would think tuning the IF correctly first would give the best results. A 1/4 turn on any of the IF trimmers is really a lot. It would be just a slight turn less than 1/8. If you don't have a signal generator, post your E-Mail address. I can send you a procedure for Aligning Without Instruments. After doing this the performance should be improved.
::
:Thank you Warren.
:Please send to nlukens1@comcast.net

Warren,

Received, thank you.
I should be able to do this.
Will start and advise after next weekend the results.

Noel
:
:Noel
: