"TC Dufresne" wrote in message
...
Hi:
I am having a problem with a "Simple Receiver for Beginners". It is from a
design that was featured in an old (1981) ARRL handbook. It is a DC
receiver, looks like alot of fun, but it isn't fun now.
Here is the problem.

1) No oscillation! I can't find it (the VFO) on my DX-398 receiver at
all,
or on my Radio Shack freq counter.
2) The power (+ side) electrolytic is supposed to be a 500uF, 16 volt. I
am
using a 470uF 35 volt. It gets really hot!! Short somewhere?!?!?!

Electrolytic capacitors are polarized. Probably you reversed the cap and
smoked it.

The VFO is REALLY simple, it has one transistor and about 7 other parts. I
can't seem to see what is wrong, and I have tried.

I would sure appreciate some Elmer'ing here!
ANY help would be much appreciated. I have the above mentioned tools at my
command, a multimeter, and an old Heathkit "scope. (which I really don't
know how to use.

Start by looking at the voltage at the electrolytic cap, and see if you in
fact have voltage or not.

Any chance?
Thanks in advance,
Tom
KCØGXX

"Carl R. Stevenson" wrote in message
...

"TC Dufresne" wrote in message
...
Hi:
I am having a problem with a "Simple Receiver for Beginners". It is from
a
design that was featured in an old (1981) ARRL handbook. It is a DC
receiver, looks like alot of fun, but it isn't fun now.
Here is the problem.

1) No oscillation! I can't find it (the VFO) on my DX-398 receiver at
all,
or on my Radio Shack freq counter.
2) The power (+ side) electrolytic is supposed to be a 500uF, 16 volt. I
am
using a 470uF 35 volt. It gets really hot!! Short somewhere?!?!?!

Are you using a tantalum capacitor? If they are inserted with the wrong
polarity they will get really hot ... sometime will actually burn.

More likely explode, sending HARD ceramic fragments in ALL directions at
HIGH velocity.

"Carl R. Stevenson" wrote in message
...

"TC Dufresne" wrote in message
...
Hi:
I am having a problem with a "Simple Receiver for Beginners". It is from
a
design that was featured in an old (1981) ARRL handbook. It is a DC
receiver, looks like alot of fun, but it isn't fun now.
Here is the problem.

1) No oscillation! I can't find it (the VFO) on my DX-398 receiver at
all,
or on my Radio Shack freq counter.
2) The power (+ side) electrolytic is supposed to be a 500uF, 16 volt. I
am
using a 470uF 35 volt. It gets really hot!! Short somewhere?!?!?!

Are you using a tantalum capacitor? If they are inserted with the wrong
polarity they will get really hot ... sometime will actually burn.

More likely explode, sending HARD ceramic fragments in ALL directions at
HIGH velocity.

In article , says...
"TC Dufresne" wrote in
:

Hi:
I am having a problem with a "Simple Receiver for Beginners". It is
from a design that was featured in an old (1981) ARRL handbook. It is
a DC receiver, looks like alot of fun, but it isn't fun now.
Here is the problem.

1) No oscillation! I can't find it (the VFO) on my DX-398 receiver at
all, or on my Radio Shack freq counter.
2) The power (+ side) electrolytic is supposed to be a 500uF, 16 volt.
I am using a 470uF 35 volt. It gets really hot!! Short somewhere?!?!?!

The VFO is REALLY simple, it has one transistor and about 7 other
parts. I can't seem to see what is wrong, and I have tried.

I would sure appreciate some Elmer'ing here!
ANY help would be much appreciated. I have the above mentioned tools
at my command, a multimeter, and an old Heathkit "scope. (which I
really don't know how to use.

Any chance?
Thanks in advance,
Tom
KCØGXX






Gotta be a short somewhere. Filter caps ain't supposed to get hot, and
yours is over rated to begin with.

and when you run an electrolytic at a different WVDC than it's rated at,
you can't be sure the capacitance is the same as marked on the can. but
it should still filter and not get hot. you'd think something else would
heat up if there was a short. should draw excessive current. unless it
blew something and is now an open, then the cap shouldn't get hot any
more.

In article , says...
"TC Dufresne" wrote in
:

Hi:
I am having a problem with a "Simple Receiver for Beginners". It is
from a design that was featured in an old (1981) ARRL handbook. It is
a DC receiver, looks like alot of fun, but it isn't fun now.
Here is the problem.

1) No oscillation! I can't find it (the VFO) on my DX-398 receiver at
all, or on my Radio Shack freq counter.
2) The power (+ side) electrolytic is supposed to be a 500uF, 16 volt.
I am using a 470uF 35 volt. It gets really hot!! Short somewhere?!?!?!

The VFO is REALLY simple, it has one transistor and about 7 other
parts. I can't seem to see what is wrong, and I have tried.

I would sure appreciate some Elmer'ing here!
ANY help would be much appreciated. I have the above mentioned tools
at my command, a multimeter, and an old Heathkit "scope. (which I
really don't know how to use.

Any chance?
Thanks in advance,
Tom
KCØGXX






Gotta be a short somewhere. Filter caps ain't supposed to get hot, and
yours is over rated to begin with.

and when you run an electrolytic at a different WVDC than it's rated at,
you can't be sure the capacitance is the same as marked on the can. but
it should still filter and not get hot. you'd think something else would
heat up if there was a short. should draw excessive current. unless it
blew something and is now an open, then the cap shouldn't get hot any
more.

In article ,
says...

Tom:

The hot cap has two likely possibilities: either the cap is shorted
internally (an ohmeter check will show leakage) or you have bad diode(s) so
AC is being applied to the cap. An ohmeter will show the diodes as bad.

a backward diode will supply AC to the cap, also


Of course a wiring error could also be involved, but I am assuming you have
double checked that.

If the cap is running hot you probably don't have the correct voltage for
the VFO, and correcting it may solve the other VFO problem.

Roger K6XQ

In article ,
says...

Tom:

The hot cap has two likely possibilities: either the cap is shorted
internally (an ohmeter check will show leakage) or you have bad diode(s) so
AC is being applied to the cap. An ohmeter will show the diodes as bad.

a backward diode will supply AC to the cap, also


Of course a wiring error could also be involved, but I am assuming you have
double checked that.

If the cap is running hot you probably don't have the correct voltage for
the VFO, and correcting it may solve the other VFO problem.

Roger K6XQ

In article ,
says...
Try contacting ARRL for corrections to the article. I built a DC rcvr from
about that time frame and it did not work. The ARRL sent corrections to the
schematic and there were a lot!!



good idea. he (OP) said 500uF cap. never heard of one. some article!

the disconnect the load and shoot the supply idea is also good. then
check the load (circuit for shorts b4 reconnecting the supply.

In article ,
says...
Try contacting ARRL for corrections to the article. I built a DC rcvr from
about that time frame and it did not work. The ARRL sent corrections to the
schematic and there were a lot!!



good idea. he (OP) said 500uF cap. never heard of one. some article!

the disconnect the load and shoot the supply idea is also good. then
check the load (circuit for shorts b4 reconnecting the supply.

Active8 wrote:
In article ,
says...

Tom:

The hot cap has two likely possibilities: either the cap is shorted
internally (an ohmeter check will show leakage) or you have bad diode(s) so
AC is being applied to the cap. An ohmeter will show the diodes as bad.


a backward diode will supply AC to the cap, also

No, it won't.

It will however supply the wrong polarity of DC, which could indeed
cause these symptoms.

I would think some other semiconductors might be running rather hot too
if that were the case.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com