Troubleshooting Tips

About Capacitors

Different cap values can be used but it depends on the circuit.

If a cap on a B+ line to ground is increased 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 altogether. Those 100 pf caps are used to remove RF from the audio signal after the detector circuit. A 200 pf would be ok but larger caps will eliminate the signal altogether.

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 from happening.

Capacitor values in tuned circuits, around the oscillator circuit, should not be changed. If a different value is used the radio probably won't align right or not at all.

Use this reference
100 pf (mmf) = .0001 mfd
1000 pf----- = .001 mfd
10000 pf --- = .01 mfd
100000 pf -- = .1 mfd

Common symptoms and remedies of noises in a old radios.

In troubleshooting with noise other than the random type, we must however recognized 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 want to share with you.

1. Steady howl on all the 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 the supply. On 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 going through it.

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

Ruff or scratchy distortion with considerable blocking on stronger stations sometime no stations at all.

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.

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 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.

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.

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