If a #47 bulb seems short lived, or runs hot in your radio, it can be
replaced with the more dim light of a 4 digit bulb type number that is
rated for 28 volts. (Check that the current drain is similar or less
than that of a #47.) There are several examples with 4 digit part nos.
I want to say from memory 1428 is one such bulb. Just verify the base is
the bayonet, opposed pins identical to the #47, and same length of brass
shell, to identically fit the lamp holder, if one is used.
The 28 volt bulbs should still be in Mouser, Digi Key, Allied and other
large distributor's catalogs.
Some years ago, we replaced many #47 bulbs with 28 volt bulbs, which we
stocked for tape recorders we owned from Ampex Corp. I think we are
down to one instrument with a 28 volt substitute, but it was a pleasure
to not have to keep ordering #47 bulbs and replacing them. Some were in
tube based instruments, some in transistor based instruments. Now
replacement instruments come with long lived LED lamps or indicators.
-Stuart Rohre
K5KVH
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