PHILCO PHORUM

Loctal Socket Troubles:
Strange Hum Problem in AC/DC Model 41-605

Having replaced all of the paper and electrolytic capacitors in this radio, I applied power for the first time to discover that the radio played well with good volume - only it had a very loud hum!

As I began troubleshooting the set the next day, suddenly it began to make loud static noise, like the sound of a close thunderstorm. Remembering my experience with the Type 75 tube (which can be notorious for producing loud static even when it tests good), I went for 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. Loctal tube sockets are notorious for developing bad contacts and should always be cleaned; I had let myself get in a hurry and failed to clean the sockets in this case. Many repairmen use a very tiny file, found in welding supply shops, to carefully clean the contacts. In my experience, a careful spraying of each contact in the tube socket, accompanied by the use of a tiny brush intended to clean between your teeth, usually does the trick. I 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!

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