Slight Ignition Noise in Radio

[TED DIMON]

My '69 has the original AM radio in it.  It works fine but there is a little ignition noise in the reception when the signal is not strong.  Do you think the ignition shielding from a '63 or '64 would solve this?

[Jim78]

The shielding from a 63-64 Studebaker engine wouldn't fit up to your Chevrolet engine.  Similar shielding was used on Corvettes, and while it is available, it's quite expensive.  Unless you are particularly attached to the old AM radio,  I think that the best solution would be to upgrade to an AM/FM.  If originality is a concern, there are vendors who can upgrade the internals of your existing radio without changing the outward appearance. 

Another option to maintain originality in appearance would be to add a modern radio in the glove box. 

Edited May 10, 2020 by Jim78

[TED DIMON]

5 hours ago, Jim78 said:

The shielding from a 63-64 Studebaker engine wouldn't fit up to your Chevrolet engine.  Similar shielding was used on Corvettes, and while it is available, it's quite expensive.  Unless you are particularly attached to the old AM radio,  I think that the best solution would be to upgrade to an AM/FM.  If originality is a concern, there are vendors who can upgrade the internals of your existing radio without changing the outward appearance. 

Another option to maintain originality in appearance would be to add a modern radio in the glove box. 

Good catch....thank you!  I am a news junky, so I only listen to AM while in a car.  Therefore, I'll check out the availability/cost of shielding for that vintage 350 engine.  I'll also check out the upgrading of the existing radio. 

[Jim78]

A complete shield set for a 350 (available from Corvette America) will set you back about $500.  And, there's no guarantee that it will solve the problem.  I would first check to see if there is a static suppression capacitor attached to the + pole of the coil.  It could be missing or bad.  Radio interference can also come from the alternator.  A suppressor there may help. 

https://shop.advanceautoparts.com/p/acdelco-ignition-capacitor-d204/3964752-P?searchTerm=rfi capacitor

https://shop.advanceautoparts.com/p/bwd-alternator-capacitor-sc139/10100275-P?searchTerm=alternator capacitor

I would also check to see if the spark plug wires are of a radio suppression type.  It is possible that over the years someone changed them to a copper core type for performance reasons.  The spark plugs should also be a resistor type.

Might there be a local automotive radio installation shop in your area?  If you can find one there, look for a gray haired guy who might know what an AM radio is, and understand your problem.  

Good luck. 

[Gunslinger]

Is the noise you hear a constant or does it go up and down with the engine rpms?  If it's constant it's ignition noise.  If it changes with engine rpms it's alternator whine.  An appropriate noise elimination condenser at the distributor or the alternator may fix the problem.  A noise filter being added under the dash in the radio power lead might help as well but it may not be necessary of the others do the job.

Check the antenna ground and make sure it's a solid connection and not corroded. The antenna may also need to be "trimmed" which is done at the radio itself.  Its pretty much a lost art but easy to do depending on the radio.  

To "Trim" the antenna, remove the tuning knob of the radio and the escutcheon behind it...you should see a small screw just behind and above the shaft.  Set the radio to as strong a station as you can find around 1400 on the dial.  Turn the screw until you get the best signal and the antenna is trimmed.  After so many years it would not be unusual to find this necessary.  

[TED DIMON]

Thank you all.  This is great input and advice.  I will try one thing at a time and avoid the shielding approach.  I don't think it is the alternator since the noise does not vary with engine RPM's.  Therefore, I will trim the antenna first, then a condenser at the distributor. 

[TED DIMON]

On 5/11/2020 at 11:24 AM, TED DIMON said:

Thank you all.  This is great input and advice.  I will try one thing at a time and avoid the shielding approach.  I don't think it is the alternator since the noise does not vary with engine RPM's.  Therefore, I will trim the antenna first, then a condenser at the distributor. 

I "trimmed" the antenna as Gunslinger suggested above.  That did the trick!  Apparently, the 51 year old radio needed a little tweaking.  Thanks, Gunslinger for your help!

I

[Gunslinger]