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

GBrown wrote:


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.

Aha! That might be it. Better (more logical) choice on caps nowadays
would be the ac-rated X-Y disc caps. Available at Mouser, Justradios, etc.

-Bill M

"-ex-" wrote in message
...
GBrown wrote:


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.

Aha! That might be it. Better (more logical) choice on caps nowadays
would be the ac-rated X-Y disc caps. Available at Mouser, Justradios,
etc.

-Bill M

Yes, Gary has a good point. I didn't expect they placed the caps
behind the fuses, most manufacturers had them right at the line
cord entry!

Pete

"Edmund H. Ramm" wrote in message
...
In vC5Oe.1983$sw6.530@fed1read05 " Uncle Peter"
writes:
Instead of dumpstering etc., what is wrong with having a new
transformer wound?

73, Eddi ._._.
--


Depends on the sentimental value. A rewound transformer would
buy TWO nice examples of the R-100 Stateside. It should be
easy to find a replacement from a junker, even from another
brand, that would work though.

Pete

" Uncle Peter" wrote in message
news:1hsOe.2111$sw6.1426@fed1read05...

"Edmund H. Ramm" wrote in message
...
In vC5Oe.1983$sw6.530@fed1read05 " Uncle Peter"
writes:
Instead of dumpstering etc., what is wrong with having a new
transformer wound?

73, Eddi ._._.
--


Depends on the sentimental value. A rewound transformer would
buy TWO nice examples of the R-100 Stateside.

Yikes! I could buy a brand new standard transformer from Hammond for
$40 -$50. No, it wouldn't be original, but would it matter? Are R-100s
really down to the $20 range?

!!!!!!!!!!!!

"BFoelsch" wrote in message
...

" Uncle Peter" wrote in message
news:1hsOe.2111$sw6.1426@fed1read05...

"Edmund H. Ramm" wrote in message
...
In vC5Oe.1983$sw6.530@fed1read05 " Uncle Peter"
writes:
Instead of dumpstering etc., what is wrong with having a new
transformer wound?

73, Eddi ._._.
--


Depends on the sentimental value. A rewound transformer would
buy TWO nice examples of the R-100 Stateside.

Yikes! I could buy a brand new standard transformer from Hammond for
$40 -$50. No, it wouldn't be original, but would it matter? Are R-100s
really down to the $20 range?

!!!!!!!!!!!!

Further to my previous message....

What I usually do in the case of a blown power transformer is as follows.

If an exact replacement transformer is not available or affordable, I buy a
good electrical replacement from Hammond or whomever. It is never a good
mechanical match, as we all know. Rather than hacking the chassis to death,
I make up an adapter plate. I take a piece of flat steel (old computer cases
are exactly the right thickness, and they're free) and drill two sets of
holes in it, one to match the original transformer, one to match the new
transformer. I then mount the adapter plate either above or below the
chassis using 8-32 hardware and spacers of the appropriate length. Next I
mount the transformer to the adapter and wire it up. This permits me to use
the "wrong" transformer, but does no damage to the collector value in case
the "right" transformer comes along; I just remove the adapter plate.

Before you dumpster the R-100, send it to me. I'll give you the price of a
new transformer for it! The R-100, if I remember correctly, has only two
windings, 600VCT and 6.3 filament. Replacing the transformer as I describe
is an easy afternoon project! Radio Daze and AES both list suitable
replacement transformers.

Just so happens, I have a good tranny from a R-100A, ready to ship, and it
doesn't blow fuses.

--
Regards,
Gary...WZ1M
" Uncle Peter" wrote in message
news:1hsOe.2111$sw6.1426@fed1read05...


"Edmund H. Ramm" wrote in message
...
In vC5Oe.1983$sw6.530@fed1read05 " Uncle Peter"
writes:
Instead of dumpstering etc., what is wrong with having a new
transformer wound?

73, Eddi ._._.
--


Depends on the sentimental value. A rewound transformer would
buy TWO nice examples of the R-100 Stateside. It should be
easy to find a replacement from a junker, even from another
brand, that would work though.

Pete

I would hope it had a primary winding to.

--
Regards,
Gary...WZ1M
"BFoelsch" wrote in message
...


"BFoelsch" wrote in message
...

" Uncle Peter" wrote in message
news:1hsOe.2111$sw6.1426@fed1read05...

"Edmund H. Ramm" wrote in message
...
In vC5Oe.1983$sw6.530@fed1read05 " Uncle Peter"
writes:
Instead of dumpstering etc., what is wrong with having a new
transformer wound?

73, Eddi ._._.
--


Depends on the sentimental value. A rewound transformer would
buy TWO nice examples of the R-100 Stateside.

Yikes! I could buy a brand new standard transformer from Hammond for
$40 -$50. No, it wouldn't be original, but would it matter? Are R-100s
really down to the $20 range?

!!!!!!!!!!!!

Further to my previous message....

What I usually do in the case of a blown power transformer is as follows.

If an exact replacement transformer is not available or affordable, I buy
a
good electrical replacement from Hammond or whomever. It is never a good
mechanical match, as we all know. Rather than hacking the chassis to
death,
I make up an adapter plate. I take a piece of flat steel (old computer
cases
are exactly the right thickness, and they're free) and drill two sets of
holes in it, one to match the original transformer, one to match the new
transformer. I then mount the adapter plate either above or below the
chassis using 8-32 hardware and spacers of the appropriate length. Next I
mount the transformer to the adapter and wire it up. This permits me to
use
the "wrong" transformer, but does no damage to the collector value in case
the "right" transformer comes along; I just remove the adapter plate.

Before you dumpster the R-100, send it to me. I'll give you the price of a
new transformer for it! The R-100, if I remember correctly, has only two
windings, 600VCT and 6.3 filament. Replacing the transformer as I describe
is an easy afternoon project! Radio Daze and AES both list suitable
replacement transformers.

Uncle Peter wrote:
"Edmund H. Ramm" wrote in message
In vC5Oe.1983$sw6.530@fed1read05 " Uncle Peter"
writes:
Instead of dumpstering etc., what is wrong with having a new
transformer wound?

Depends on the sentimental value. A rewound transformer would
buy TWO nice examples of the R-100 Stateside. It should be
easy to find a replacement from a junker, even from another
brand, that would work though.

If it's just the HV winding, you can do the rewinding yourself. It won't
cost much, and it'll be fun.
--scott

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

If you dig that deep into the tranny, mite as well rewind the primary as
well.

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

Uncle Peter wrote:
"Edmund H. Ramm" wrote in message
In vC5Oe.1983$sw6.530@fed1read05 " Uncle Peter"
writes:
Instead of dumpstering etc., what is wrong with having a new
transformer wound?

Depends on the sentimental value. A rewound transformer would
buy TWO nice examples of the R-100 Stateside. It should be
easy to find a replacement from a junker, even from another
brand, that would work though.

If it's just the HV winding, you can do the rewinding yourself. It won't
cost much, and it'll be fun.
--scott

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

"BFoelsch" wrote in message
...


Depends on the sentimental value. A rewound transformer would
buy TWO nice examples of the R-100 Stateside.

Yikes! I could buy a brand new standard transformer from Hammond for
$40 -$50. No, it wouldn't be original, but would it matter? Are R-100s
really down to the $20 range?

!!!!!!!!!!!!



Well, I may have overstated that. But, I see nice ones going in the
50 to 60 dollar range, and ones that would make good parts units
in the 20 dollar range on ePay.

But, most likely it was the linebypass caps as others noted, and
not the transformer.

Pete