[R-390] Blowing B+ fuse

[Barry]

> > I finally got a couple of 1/8A B+ fuses (SloBlo)
>
> I think that the B+ fuses are supposed to be non-sloblo (fastblow).
> The idea is that a short/overload on the B+ should break the circuit
> immediately.
>

I figured they were all SloBlo, but maybe not.  Any other comments here?

> Incidentally both my R-390A's came to me with 2 or 3A fuses in the B+
> positions.  May as well have been a penny...
>

The reason I've been running with the 1/4A is: 1) It's what I had on hand,
and 2) The older radios didn't have this fuse at all.  I figured if
something catastrophic occurred, the 1/4A *might* protect something, but a
"penny" would have been the same as the older radios so I wasn't too
worried.

> > [Blowing fuse = bad electrolytic filters]
>
> Probably.  Do the electrolytic cans get noticeably hot (hotter than
> the chassis around them at least?)
>

If I recall, the caps do get a bit warm (at least one of them).  I'll do a
current check with the cans and the new caps and see what difference it
makes.

> It's entirely possible for the electrolytics to still have enough
> capacitance to effectively filter but have so much leakage that
> they blow the fuse.
>
> Also check for burnt resistors on the decks... indication that
> a tube is drawing way too much current.
>

I didn't notice any obviously burned resistors when I recapped the decks.  I
could have some high values, but none looked obvious.

> The army manual has a good procedure for finding B+ shorts with an
> ohmmeter but it doesn't always show up too-much-current-when-real-power-
> applied faults.
>
> Tim.

I need to do a resistance/voltage check on all tube pins before I call this
one complete.  Hopefully, I can get things going with the 1/8A fuse with the
electrolytic changes, but if not, I have other issues.

Thanks,

Barry - N4BUQ