01-23-2008, 10:18 AM
Everyone seems to be on the same track!
As for the BED (color code= body-end-dot) or "dogbone" resistors- start with the higher values first - above 5K- these are the ones that will be the most out of tolerance and will cause popping and sudden changes in volume. The lower value BED resistors generally retain proper resistance and don't cause many problems. More simply, any resistor with an orange, yellow, or green dot MUST be changed; the reds come next if necessary.
Audio tube sockets are a major cause of intermittents- I suggest that you take out the audio tube (tubes) and squeeze the socket contacts slightly with needle-nosed pliers. Wiggle the tube around a bit when reinserting it. Audio tubes run quite hot and allow metal fatigue and contact oxides to develop in the sockets.
I strongly suggest a contact cleaner that contains "cramolin". I have been using the same 2 oz. bottle of pure industrial Cramolin for about 40 years but I dilute it about 100:1 with wood alcohol, and apply with a fine needle syringe. Ten diluted drops will service an entire radio, including pots. Cramolin cleaners are on Ebay- use it VERY sparingly, applying with a toothpick only.
A lousy volume control pot is most often from the carbon resistor layer being worn through; these can't be fixed. RadioDaze has lots of replacement pots with switches that the buyer configures. Don't torture yourself with a ratty worn-out pot- replace it.
Before long you will have a great 620!
As for the BED (color code= body-end-dot) or "dogbone" resistors- start with the higher values first - above 5K- these are the ones that will be the most out of tolerance and will cause popping and sudden changes in volume. The lower value BED resistors generally retain proper resistance and don't cause many problems. More simply, any resistor with an orange, yellow, or green dot MUST be changed; the reds come next if necessary.
Audio tube sockets are a major cause of intermittents- I suggest that you take out the audio tube (tubes) and squeeze the socket contacts slightly with needle-nosed pliers. Wiggle the tube around a bit when reinserting it. Audio tubes run quite hot and allow metal fatigue and contact oxides to develop in the sockets.
I strongly suggest a contact cleaner that contains "cramolin". I have been using the same 2 oz. bottle of pure industrial Cramolin for about 40 years but I dilute it about 100:1 with wood alcohol, and apply with a fine needle syringe. Ten diluted drops will service an entire radio, including pots. Cramolin cleaners are on Ebay- use it VERY sparingly, applying with a toothpick only.
A lousy volume control pot is most often from the carbon resistor layer being worn through; these can't be fixed. RadioDaze has lots of replacement pots with switches that the buyer configures. Don't torture yourself with a ratty worn-out pot- replace it.
Before long you will have a great 620!
Pete AI2V
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