Knight R-100A Keeps Blowing Fuses
 

Knight R-100A Receiver dropped dead while listening, and hoping to get
back on the air if only with a "nostalgia" station. The fuse had
blown. No previous problems. I replaced the fuse, turned it on,
the dial lights glowed dimly for a couple of seconds, long enough for
me to say "that's not good". Then the fuse blew again.

Preliminary checks don't show anything visibly shorted.

Any suggestions appreciated. TNX es 73, Mike

Sounds like either the rectifier has failed, or the filter caps.
Try it REAL quick with the rectifier tube pulled, on hand on
the line cord.

Pete


"KE9EX" wrote in message
oups.com...
Knight R-100A Receiver dropped dead while listening, and hoping to get
back on the air if only with a "nostalgia" station. The fuse had
blown. No previous problems. I replaced the fuse, turned it on,
the dial lights glowed dimly for a couple of seconds, long enough for
me to say "that's not good". Then the fuse blew again.

Preliminary checks don't show anything visibly shorted.

Any suggestions appreciated. TNX es 73, Mike

I did try that... The slo blo fuse blew after a second. This should
have removed power from the filter caps. Does this indicate that the
problem lies elsewhere than the Power supply? Thanks.

Uncle Peter wrote:
Sounds like either the rectifier has failed, or the filter caps.
Try it REAL quick with the rectifier tube pulled, on hand on
the line cord.

Pete


"KE9EX" wrote in message
oups.com...
Knight R-100A Receiver dropped dead while listening, and hoping to get
back on the air if only with a "nostalgia" station. The fuse had
blown. No previous problems. I replaced the fuse, turned it on,
the dial lights glowed dimly for a couple of seconds, long enough for
me to say "that's not good". Then the fuse blew again.

Preliminary checks don't show anything visibly shorted.

Any suggestions appreciated. TNX es 73, Mike

KE9EX wrote:
Knight R-100A Receiver dropped dead while listening, and hoping to get
back on the air if only with a "nostalgia" station. The fuse had
blown. No previous problems. I replaced the fuse, turned it on,
the dial lights glowed dimly for a couple of seconds, long enough for
me to say "that's not good". Then the fuse blew again.

Preliminary checks don't show anything visibly shorted.

Check supply caps. Check rectifiers.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I have a different receiver that continually blew fuses. I eventually
determined that it was a bad power transformer, probably a shorted
winding, since it blows fuses with the secondary completely
disconnected. I hope this is not your problem. Good luck.

In article .com,
wrote:
I have a different receiver that continually blew fuses. I eventually
determined that it was a bad power transformer, probably a shorted
winding, since it blows fuses with the secondary completely
disconnected. I hope this is not your problem. Good luck.

If it blows fuses with the rectifier tube removed, this is almost
certainly the problem.

But, the good news is that when this happens, the shorted turn is
almost always on the (very fine wire) HV secondary, which is the
top winding in the bundle and the easiest thing to rewind.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Scott Dorsey" wrote in message
...
In article .com,
wrote:
I have a different receiver that continually blew fuses. I eventually
determined that it was a bad power transformer, probably a shorted
winding, since it blows fuses with the secondary completely
disconnected. I hope this is not your problem. Good luck.

If it blows fuses with the rectifier tube removed, this is almost
certainly the problem.

But, the good news is that when this happens, the shorted turn is
almost always on the (very fine wire) HV secondary, which is the
top winding in the bundle and the easiest thing to rewind.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I'd suggest removing all of the secondary windings at this point.
It could be a wiring problem--such as a pilot lamp socket
shorting out, or even arcing in the rectifier tube socket.
You have nothing to lose. The dim bulb test on a transformer
will the secondaries unloaded will reveal a shorted winding
quickly.

If it is the transformer, I suspect the radio should have some
burnt odor to it. They usually take several minutes of cooking
to fail to that degree.

Next step is dumpstering/parting the receiver, or finding a
donor. Those R-100s are problematic with the PCB
style bandswitches...

Pete

Most always the HV winding is under the filament windings. HV windings are
not the easiest to wind.

--
Regards,
Gary...WZ1M
"Scott Dorsey" wrote in message
...

In article .com,
wrote:
I have a different receiver that continually blew fuses. I eventually
determined that it was a bad power transformer, probably a shorted
winding, since it blows fuses with the secondary completely
disconnected. I hope this is not your problem. Good luck.

If it blows fuses with the rectifier tube removed, this is almost
certainly the problem.

But, the good news is that when this happens, the shorted turn is
almost always on the (very fine wire) HV secondary, which is the
top winding in the bundle and the easiest thing to rewind.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Mike:
I had this problem with the same receiver. It is the line bypass caps.
One or both are no good. Replace with 1600 volt discs and your problem is
solved.

--
Regards,
Gary...WZ1M
"KE9EX" wrote in message
oups.com...
Knight R-100A Receiver dropped dead while listening, and hoping to get
back on the air if only with a "nostalgia" station. The fuse had
blown. No previous problems. I replaced the fuse, turned it on,
the dial lights glowed dimly for a couple of seconds, long enough for
me to say "that's not good". Then the fuse blew again.

Preliminary checks don't show anything visibly shorted.

Any suggestions appreciated. TNX es 73, Mike