[R-390] Blown B+ Fuse - Cont'd

Barry N4BUQ at aol.com
Sat Jul 9 23:56:03 EDT 2005


That is certainly plausible.  I turned the radio on its side to get at the
fuse so the tubes are in a different gravitational orientation than when the
fuse blew.  I didn't even check the tubes before cranking this thing up and
I really should do that.  The leakage/short test may hav some surprises
waiting for me.

I plan to try this with the fuse inline with the meters.  If it blows when
the circuit is drawing significantly less than 125mA, then I'm guessing a
bad set of fuses.

Thanks!

Barry - N4BUQ

----- Original Message -----
From: <Flowertime01 at wmconnect.com>
To: <R-390 at mailman.qth.net>
Sent: Saturday, July 09, 2005 10:28 PM
Subject: Re: [R-390] Blown B+ Fuse - Cont'd


> Barry,
>
> First thought on this is a tube doing an internal short.
> Something flaked inside a tube and gives you an over current.
> So you bumped the receiver around and now it behaves.
>
> The 1/8 amp is out after the filter supply caps.
> So it looks like a by pass cap in the RF- IF B+ line.
> And the switched RF-IF B+ Line.
>
> If the receiver is still killing 1/8 amp fuses, put the tubes in the
tester
> and
> smack them around a bit. In the past blown fuses were bad tubes.
> If you have this receiver all recapped, I would expect a tube is erratic.
>
> Second though on this is a poor cap.
> It looks to have reformed its self for the time being.
> If you keep the voltage on and carefully watch the critter it looks like
it
> will
> behave. If you let the receiver cool for a few days, the problem could
> reappear.
> But a tube will do the same thing to you.
>
> It may not be the cap per say. It could be a left over grim or
condensation
> problem.
> Two much current leaking off a wire to ground. Just as hard to find as a
> marginal tube or cap.
>
> Roger KC6TRU
>
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