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

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

In article , lid
says...
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.

oops. right. 1 diode backwards in a full wave (not a bridge) rectifier
would short the xfrmr.

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.

If you're using a diode bridge like most people do these days, and the
diode bridge output terminals (+ and -) are reversed, the filter
capacitor would get hot and the receiver wouldn't work.

As others have pointed out, an electrolytic capacitor with reverse
voltage applied can catch fire or explode. Be careful when
troubleshooting while the capacitor is unhappy. When you do find the
problem, it would be a good idea to replace the capacitor.

Roy Lewallen, W7EL

Active8 wrote:
In article , lid
says...

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.


oops. right. 1 diode backwards in a full wave (not a bridge) rectifier
would short the xfrmr.

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.

If you're using a diode bridge like most people do these days, and the
diode bridge output terminals (+ and -) are reversed, the filter
capacitor would get hot and the receiver wouldn't work.

As others have pointed out, an electrolytic capacitor with reverse
voltage applied can catch fire or explode. Be careful when
troubleshooting while the capacitor is unhappy. When you do find the
problem, it would be a good idea to replace the capacitor.

Roy Lewallen, W7EL

Active8 wrote:
In article , lid
says...

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.


oops. right. 1 diode backwards in a full wave (not a bridge) rectifier
would short the xfrmr.

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.

In article , lid
says...
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.

oops. right. 1 diode backwards in a full wave (not a bridge) rectifier
would short the xfrmr.

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.

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

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

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.

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

"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?!?!?!

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.

It's a good idea to build things in stages, testing each stage as you go.

Try disconnecting everything from the power supply and sort that out first.
The capacitor shouldn't get hot.

73, Leon
--
Leon Heller, G1HSM

http://www.geocities.com/leon_heller