:Hi Norm
I have a stupid question, I'm trying to determine which side of the original diode is Cathode and Anode, according too the SAMS the Cathode is connected to the IF coil and the Anode is connected too the next stage via of resistor/coil parallel, the original diode has a tappered side and a flat side, the way it was in ckt, I'm guessing the tappered side is the Cathode, and the flat side is the Anode, if this is the case then the SAMS is wrong, do you have any ideas on this, I don't dare put the new one in until I know for sure the polarity is right.
Mark

The general convention is that the cathode end of a diode (wire lead mount) has a band marking. Some manufacturers used a taper to indicate the cathode end, but this was usually only on power rectifiers in plastic encapsulated cases, not on signal diodes.
Rich

::Hi Norm
: I have a stupid question, I'm trying to determine which side of the original diode is Cathode and Anode, according too the SAMS the Cathode is connected to the IF coil and the Anode is connected too the next stage via of resistor/coil parallel, the original diode has a tappered side and a flat side, the way it was in ckt, I'm guessing the tappered side is the Cathode, and the flat side is the Anode, if this is the case then the SAMS is wrong, do you have any ideas on this, I don't dare put the new one in until I know for sure the polarity is right.
:Mark
:

:The general convention is that the cathode end of a diode (wire lead mount) has a band marking. Some manufacturers used a taper to indicate the cathode end, but this was usually only on power rectifiers in plastic encapsulated cases, not on signal diodes.
:Rich
:
:::Hi Norm
:: I have a stupid question, I'm trying to determine which side of the original diode is Cathode and Anode, according too the SAMS the Cathode is connected to the IF coil and the Anode is connected too the next stage via of resistor/coil parallel, the original diode has a tappered side and a flat side, the way it was in ckt, I'm guessing the tappered side is the Cathode, and the flat side is the Anode, if this is the case then the SAMS is wrong, do you have any ideas on this, I don't dare put the new one in until I know for sure the polarity is right.
::Mark
::Hi Rich
I understand that, but the diode that is in there is a plastic encapsulated Tappered type, and it is a Germanium Detector diode, this is the delma I'm facing, is there a way too tell by resistance measurement too determine which is which?
Mark

I have an original copy of the manual for a Heathkit TC-2 tube tester, printed in 1953. The schematic shows a diode backwards from the way it should be (and the way it was actually installed). If the diode were installed the way it was shown, the meter swings backwards.

I was told that this was likely not an error, that in those days there was not a uniform convention for showing a diode's polarity. Seems hard to believe.

(Now, of course, the bar is toward the cathode and the arrowhead points away from the anode, in the direction of conventional positive current flow - but that Heath manual has it the other way around.)

:I have an original copy of the manual for a Heathkit TC-2 tube tester, printed in 1953. The schematic shows a diode backwards from the way it should be (and the way it was actually installed). If the diode were installed the way it was shown, the meter swings backwards.
:
:I was told that this was likely not an error, that in those days there was not a uniform convention for showing a diode's polarity. Seems hard to believe.
:
:(Now, of course, the bar is toward the cathode and the arrowhead points away from the anode, in the direction of conventional positive current flow - but that Heath manual has it the other way around.)
Well there was a mark on the original diode at one time, but do too age it has long since worn off, so I have no idea which way to put this new diode in, in relation too the old one, until I can find a definitive way of determining which way to put the new one in, I just can't risk it.
Mark

Mark

If not sure try both directions. A Video Detector is similar to a crystal set. There is very little voltage and the diode should work in either direction. Try both ways to see if there is any difference?

Norm

::I have an original copy of the manual for a Heathkit TC-2 tube tester, printed in 1953. The schematic shows a diode backwards from the way it should be (and the way it was actually installed). If the diode were installed the way it was shown, the meter swings backwards.
::
::I was told that this was likely not an error, that in those days there was not a uniform convention for showing a diode's polarity. Seems hard to believe.
::
::(Now, of course, the bar is toward the cathode and the arrowhead points away from the anode, in the direction of conventional positive current flow - but that Heath manual has it the other way around.)
:Well there was a mark on the original diode at one time, but do too age it has long since worn off, so I have no idea which way to put this new diode in, in relation too the old one, until I can find a definitive way of determining which way to put the new one in, I just can't risk it.
:Mark

:Mark
:
: If not sure try both directions. A Video Detector is similar to a crystal set. There is very little voltage and the diode should work in either direction. Try both ways to see if there is any difference?
:
:Norm
:Hi Norm
I did notice one thing, in checking both diodes with the Digital VOM, I noticed that in one direction they both have about the same resisitance, around .650K, which would mean that the cathode does in fact go to the 4th IF Amp coil, as the schematic states, going to connect the new diode in this manner and see what happens, hopefully this will solve the picture problem.
Mark
:::I have an original copy of the manual for a Heathkit TC-2 tube tester, printed in 1953. The schematic shows a diode backwards from the way it should be (and the way it was actually installed). If the diode were installed the way it was shown, the meter swings backwards.
:::
:::I was told that this was likely not an error, that in those days there was not a uniform convention for showing a diode's polarity. Seems hard to believe.
:::
:::(Now, of course, the bar is toward the cathode and the arrowhead points away from the anode, in the direction of conventional positive current flow - but that Heath manual has it the other way around.)
::Well there was a mark on the original diode at one time, but do too age it has long since worn off, so I have no idea which way to put this new diode in, in relation too the old one, until I can find a definitive way of determining which way to put the new one in, I just can't risk it.
::Mark

Mark, when you test the diode with your meter, use the most sensitive meter setting (like X10,000 or whatever moves the meter the most when you touch it with your fingers).

When you test your diode, it should have some continuity in one direction, but most good diodes should have NO continuity in the other direction. Continuity in the other direction makes detectors less efficient, and possibly inoperable. With power supplies, electrolytics get destroyed with diodes which have reverse leakage.

In my experience, the small germanium and similar type diodes used for detectors usually have no reverse leakage.....well, then again germanium sometimes does. Ask Norm if he thinks that leakage is bad. Maybe it isn't.

Thomas

:Mark
:
: If not sure try both directions. A Video Detector is similar to a crystal set. There is very little voltage and the diode should work in either direction. Try both ways to see if there is any difference?
:
:Norm
:Hi Norm
Well I determined which way the diode went in, unfortunately, still the same result, weak picture, at this point I must admit, I'm just about too throw in the towel on this one, I just don't know where too go from here.
Mark
:::I have an original copy of the manual for a Heathkit TC-2 tube tester, printed in 1953. The schematic shows a diode backwards from the way it should be (and the way it was actually installed). If the diode were installed the way it was shown, the meter swings backwards.
:::
:::I was told that this was likely not an error, that in those days there was not a uniform convention for showing a diode's polarity. Seems hard to believe.
:::
:::(Now, of course, the bar is toward the cathode and the arrowhead points away from the anode, in the direction of conventional positive current flow - but that Heath manual has it the other way around.)
::Well there was a mark on the original diode at one time, but do too age it has long since worn off, so I have no idea which way to put this new diode in, in relation too the old one, until I can find a definitive way of determining which way to put the new one in, I just can't risk it.
::Mark

Mark

Do you have an oscilloscope? You could check the video signal from detector to picture tube. Since you already changed the video detector check the video amplifiers.

Later TV's used the same IF amplifiers for video and sound. Early TV's has separate amplifiers. Check video IF amplifiers after sound take off.

You could feed in a video signal from VCR to the detector. This will give you a known signal to work with...

Thomas was discussing leakage. Silicon diodes will show no leakage in one direction and somewhere around half way on an ohm scale in the other. Germanium diodes may show some leakage even in the reverse direction. It depends on the meter scale and diode. They are still good.

Norm

::Mark
::
:: If not sure try both directions. A Video Detector is similar to a crystal set. There is very little voltage and the diode should work in either direction. Try both ways to see if there is any difference?
::
::Norm
::Hi Norm
: Well I determined which way the diode went in, unfortunately, still the same result, weak picture, at this point I must admit, I'm just about too throw in the towel on this one, I just don't know where too go from here.
:Mark
::::I have an original copy of the manual for a Heathkit TC-2 tube tester, printed in 1953. The schematic shows a diode backwards from the way it should be (and the way it was actually installed). If the diode were installed the way it was shown, the meter swings backwards.
::::
::::I was told that this was likely not an error, that in those days there was not a uniform convention for showing a diode's polarity. Seems hard to believe.
::::
::::(Now, of course, the bar is toward the cathode and the arrowhead points away from the anode, in the direction of conventional positive current flow - but that Heath manual has it the other way around.)
:::Well there was a mark on the original diode at one time, but do too age it has long since worn off, so I have no idea which way to put this new diode in, in relation too the old one, until I can find a definitive way of determining which way to put the new one in, I just can't risk it.
:::Mark

Generally, with tube type radios, the plate of a tube detector faces the IF transformer, and the cathode faces the chassis. The other end of the IF transformer is then connected to the grid of the 1st AF tube through a condenser and potentiometer (or coils and resistors as you say--these filter tone). Placing the cathode towards the IF transformer will reverse the phase of the audio, and depending upon how the radio is wired, may necessitate re-thinking the AVC circuit, if one is used. Also, if this reverse phase radio is played next to another radio wired using the previously mentioned diode orientation, they will be out of phase with eachother, and the audio will suffer.

This really isn't important, though. Most people don't play two AM radios next to eachother, and if you want to play your whole collection at the same time, there's going to be phase cancellation anyway. These aren't high fidelity stereos. They're just AM radios, some of them quite good, but still AM. It isn't that important. All that is important is that a new diode be installed in the same direction as the old one. A radio will work with the diode installed in either direction. Audio rides on both sides of the carrier wave. Reversing the diode might affect other circuitry, though, like the AVC circuit. Obviously with a tube, you can't install it backwards. You can change the wiring under the chassis perhaps, though with some tubes like the dual-diode-triode tubes, this is difficult, as the cathode also serves for the triode part. With a solid state diode, you can install it any way you wish. Installing it correctly is only important for the reasons mentioned above (which are very important reasons).

Thomas

Little did I know that you may be the same Mark with the picture tube problem...and in that case this would be a video detector. (I should have read your other post.) As Norm just said, though, polarity may make little difference. Pictures for television are sent out via the Amplitude Modulation system, and are detected in almost the same way as AM audio is detected.

I don't wish to overstate an obvious thing.. but just in case:
If you need to identify the polaraity on a solid state diode that isn't clearly marked or has puzzling markings... then use your ohm meter to see which way it conducts. If this too confuses you... then take a known, clearly marked, diode with a band at the cathode end. Put the neg black lead of the ohm meter there and the red pos lead on the other side. It sould conduct in this direction and not when reversed. Then perform the test on your 'unknown' diode and after observing the similar conduction directions you can mark it yourself however you wish but the best is a band on the cathode end.