Troubleshooting Tips


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About Capacitors
Different capacitor values can be used, but it depends on the circuit.
If a cap on a B+ line to ground is increased, you probably won't notice a difference. You could use 1 mfd instead of .01 mfd on a screen grid to ground and not make any difference.
If an audio coupling cap between plate of one stage and grid of the next is increased, the radio will have better low frequency response. .01 mfd can be increased to .05 mfd but very large values may start a radio motorboating.
Increasing caps on signal lines to ground reduces high frequency response. If on RF lines to ground can eliminate the signal. Those 100 pf caps are used to remove RF from the audio signal after the detector. 200 pf would be ok but large caps will eliminate all signal.
In some cases a cap is needed across signal lines to reduce high frequency response. Without these caps a high pitch sound may be heard. It's a good idea to have a .002 to .01 mfd across the output transformer primary to prevent this feedback.
Cap values in tuned circuits, around the oscillator, should not be changed. If a different value is used the radio may not align.

Use this reference

  • 100 pf (mmf) = .0001 mfd
  • 1000 pf----- = .001 mfd
  • 10000 pf --- = .01 mfd

    Common symptoms and remedies of noises in a old radio.

    Troubleshooting with noise other than the random type, we must however recognize the latter when it bears a relation to other troubles. One advantage in tracing noise problems or troubles is that most noises have a characteristic sound or sounds, which allow us to classify each type when we hear it. The type of sound gives a clue to its possible causes. These remedies are just some of the permanent fixes I have encountered.

    • 1. Steady howl on all stations. Oscillator grid resistor has changed values, check and replace if necessary.
    2. Defective oscillator tube, replace if necessary, defective output filter capacitor in power supply, and battery receivers, it could be the defective decoupling capacitor connected across the B - battery input.
    3. Defective resistors or capacitors in decoupling network.

    Steady rushing noise over part, or all, of the tuning ranges, with traces of some signals through it.

    1. Probably the local oscillator is super regenerating - that is, it is going rapidly in and out of oscillation.
    2.Remedy oscillator grid leak resistor has changed value to a much higher value than it should be.

    Ruff or scratching distortion with considerable blocking on stronger stations.

    1. Defect in AVC system, check for improper values of load resistors and capacitors in detector and AVC circuits.
    2. Main AVC bypass capacitor (usually 0.5uf ) short-circuited or leaky, short circuit cathode resistor or bypass capacitor, short circuit in bypass capacitor at low end of grid windings of RF and IF transformers.

    Fuzzy Rattling and Buzzing with AF Signal.

    1. Dirt or other foreign matter between voice coil and pole piece of speaker. Blow foreign matter out with gentle air pressure.
    2. Foreign matter on or against speaker on speaker cone. Remove.
    3. Speaker rim does not fit tightly against hole in cabinet, and vibrate against cabinet. Install rubber or felt gasket around rim.
    4. Cabinet resonates at certain frequencies, and loose parts vibrate.
    Tightened loose parts and try to deaden resonat by adding felt inside of cabinet.

    Steady whistle heterodyne sweeps rapidly back and forth across desired signal during normal reception, or gradually lowers or raises in pitch and settles at one steady tone without any adjustments of the radio receiver.

    1. Excessive radiation from interfering with a receiver, or two receivers using same antenna or antenna lead, or the other receivers oscillator is radiating a signal at a desired station frequency and is heterodyning with the desired stations signal in your receiver.
    Note: Unfortunately, it is not feasible to construct low-priced receivers in which oscillator radiation is so that nearby receivers cannot pick it up. Of course, and more elaborate receivers with RF amplifiers, radiation is negligible and this trouble is seldom experience.

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