I have a very nice Drake L-7. It has been in storages for years and I
just got it going this past fall. Stock as a rock, low serial number of
134. Original tubes.
Last weekend I was operating, everthing normal, full output 1200+ but I
started to smell something burning. Not bad, like maybe something has
fell against one of the tubes. I finally got time to look inside.
Using my nose, I quickly found the smell coming from the filament
transformer. Oh no!, but wait, it wasn't from the tranformer but a the
junction of the filament transformer and filament choke. At this
intersection, Drake has a PC Board which the connection is made. There
is also a .05 Cap to ground and a connection for the meter lamps. It is
the PC Board that is burning and making the smell.
Something on one side of the of the filament transformer is drawing too
much current. I suspect a filament-to-grid short in one of the
tubes(?).
Drake cautions as not to defeat the interlock but on the L-7 the
cabinet is closed so there is not way to see the tubes without the cover
on.
So before I go any farther, I thought I would asked the "Experts". Any
ideas, or comments? BTW this junction is the same as on a SB-220 if you
want to look at the SB220 Diagram on Measures WebPage.
Thanks Joe KØBX
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