Do the following, re-solder all joints, even if they look good. Caveat, any joint that is fastened to a molded part or to a coil form should be loosened first. Some parts are made of a molded shellac compound that will deform and flow at soldering temperature, coil forms can be made of celluloid which could ignite. I have had this happen and ruin a corner of the form.
Check all tuning condenser rotors for continuity, often the contact blade is dirty or the pigtail is broken
Loosen, move about and re-tighten all electromechanical connections even if they are currently tight.
Circuit returns to filament will be to "A-" for all circuits except for the detector if it is grid leak to "A+". This is how some of the grid bias is achieved via voltage drop in the rheostat.
Many encounter 20's era sets and attempt to operate the "A" supply at 5 volts. This is too low to muster activity in the thoriated filament of a good tube.
Raise the "A" supply to 6 to 6.6 volts, that is the voltage of fresh and fully charged lead/acid battery for which they were designed for.
If using 201A tubes be sure they are all the "A" version, do not mix with the 201 tube.
Depending if bias connections are available, a 112 or 171a can be used in the last audio.
The detector grid leak is generally 2 megohms, up to as much as 8 megohms. With the grid leak resistor disconnected, check the leakage of the detector grid capacitor, it should be infinite. Use an analog meter or a service capacitor checker at 200 volts. Looking for 250pf, but 100 to 300 pf will be O.K. If capacitance is O.K. but leakage, deduct leakage from the desired range and replace the OEM grid leak, some OEM grid leaks resistor can be "stuffed" with new resistor.
The pins of 20's era tubes are soldered with a high tin solder. This causes inter-granular corrosion over the 90 years. File the end of the pin down 1/16" and then de-solder using the application of new solder then extract, clean the inner edge of the pin and the wire with the pointed Exacto blade. Use liquid flux and re-solder, heat-sink the pin as Bakelite will blister, loosening the pin...
The thoriated tubes can be re-rejuvenated several times before the thorium is fully consumed, it is possible to get some 5K+ hours of life, instructions are published all over the web.
First step rejuvenation is to burn filaments for an hour no plate or grid connection at 6 volts ('01a). If O.K. done, subsequent steps include flashing and aging voltages, all done no connection to grid or plate...
Since this is a Neutrodyne, it is possible that it is no longer neutralized. However, that would not stop the set from working, it will simply oscillate at some tuner setting, a dummy tube (open filament) is needed or a method to turn off one leg of the filament. Come back here for instructions, it is easy but but methodology is surprising.
DO use at least 18 ga wire for the filament leads to the "A" supply if using '01's, the "A" must be 6 to 6.6 volts at the terminals of the set.
If the tube type is not designated by the radio data,it is possible that the set may be very early and use 1 amp 201 tubes. This can be seen by the use of very low resistance rheostats. In the 20's radio enthusiasts often confused tubes and put early 1 amp tubes into a set designed for 1/4 amp tubes, this often roasted the rheostats.
Any tube that tests gassy should be reserved for the detector. Using gassy tubes in the RF or AF locations will result in high B current and distortion.
The AES battery set power supply will not support more than two or three 201 (one amp) tubes.
Be aware the first digit in this series of tubes is usually assigned to the manufacturer, 201a is RCA, 301a is Cunningham, 401a is Deforest, etc. Odd manufacturers often used "X"
Note the output circuit must have at least a 2000 ohm resistance load either a magnetic headphone or speaker. A salvage output transformer can be pressed into service to a PM speaker but do not expect good efficiency. When using diaphragm headphones or a magnetic diaphragm speaker the plate current must flow through the windings and pull the diaphragm inward, wrong connection will eventually discharge the magnet. Armature speakers or Baldwin type phones are bi-polar.
Do use a 25 to 50 foot antenna, too long an antenna is not good, causes overload. Do use a short path of wire to an EARTH ground, do not ground to the electrical service even if it "seems" to work better. Such a response indicates reception from the ground path which will include all the electrical noises in the home.
Occasionally, there will be a bad mica stack or paper bypass capacitor, this is rare, good old caps are still floating around. However, cased paper bypass cap can be stuffed with a new resin dipped.
Sometimes the "B" circuits will need bypassing, this happens when using a power supply, generally a 1 MF cap at the supply Detector, amp and last audio each to B-
Operational note, never operate a battery set in an electrical storm, static discharges can abruptly cutoff the plate current in the audio and cause a kickback than can flash-over in the windings of the audio transformer(s). Some radios include a small mica cap across the windings to bypass such a surge, limit frequency response and bypass RF around the transformer.
That should get your radio working, unless someone has creatively re-wired it
GL
Chas
Subject: Re: Lafayette Neutrodyne Receiver 
August 15th 2018, 4:34 am
