Tech Section: Loctal Socket Problems and Their Cure
Having replaced all of the paper and electrolytic capacitors in a Philco 41-605, power was applied for the first time. The radio played well with good volume - only it had a very loud hum!
The next day, the radio suddenly began to make loud static noise, like the sound of a close thunderstorm. Remembering an experience with the Type 75 tube (which can be notorious for producing loud static even when it tests good), the decision was made to go after the 7C6 second detector/first audio tube. Wiggling this tube not only made the static stop, but also ended the hum.
Thoroughly cleaning the tube socket with contact cleaner, and replacing the 7C6, cured the trouble.
Bad loctal tube socket contacts can produce a multitude of symptoms, including intermittent or no reception.
Loctal tube socket contacts should always be cleaned; in this case, they had not been. Many repairmen use a very tiny file, found in welding supply shops, to carefully clean the contacts. Another approach is to carefully spray each contact in the tube socket, accompanied by the use of a tiny brush intended to clean between your teeth, in each socket contact hole. Spray contact cleaner into all eight holes of the socket, one at a time, then insert and remove the brush several times to work the contact cleaner in before it evaporates. Do this to every loctal socket in the set.
Important: Wait a while before you apply power again, however, to allow the cleaner residue to completely evaporate.