TP4 waveform wrong?

[exciter]

shouldnt i be able to adjust main delay at Tp6??
when measuring with my scope on tp6, moving the main delay pot changes nothing on screen but audio tone is changing, beeping...
when changing secondary delay, i can change delay on tp8.

[exciter]

oh i see, i need a two channel scope ;(
only have one channel...

by the way- why does the edit button disappear several minutes after posting??

[Reg]

Hi Exciter,

It is easier to see the adjustments of the delay using a dual scope, but it can be done with a single trace scope also.

If you increase the sensitivity a little on the scope and then look at TP 4, the output of the preamp and look carefully at the trace, you should see a small bump or ripple move left or right when you adjust the delay. This bump or ripple will slide along the decay curve signal trace.

What you will see is somewhat like you see on Fig's 27, 28. and 30 on the HH article. If you look closely at those pictures (pics) and look at the tp 6 signal which is the upper trace, you will see a small wiggle or bump directly on the decay curve, directly above the pulse on the bottom trace. That small bump or wiggle is the delay signal. If you adjust the delay pot, you should see that little wiggle move left or right, depending upon which way you turn it.

Also, if you adjust the sample width pot, you should see that wiggle get wider and narrower.

Now, this sample or wiggle indication is not a large signal on the decay curve, so you will have to look carefully to see it, but it can be seen. Some times it is easier to see by increasing the sensitivity of the scope so the decay curve signal is bigger.

Let me know if this makes sense.

Reg

[exciter]

Hi Reg!
im sorry for my many questions
so i followed your instructions.
here a picture. i hope i have understand it:
i dont tuned the main/sec width yet.

[Reg]

Hi Exciter,

First, your pic is upside down. Do you have your scope on invert? If you do, you might want to turn off the invert.

Now, when you carefully look at the pic you posted, you will see 4 small bumps. The left trace half shows this better than the right half.

Now, I suspect the first two bumps are actually the pulse delay and the distance between the first two bumps is the pulse width. The later two bumps are the secondary delay and the distance between them is also the width.

To know for sure, look at the same test point and adjust the sample width, R46. You should see the distance between the first two bumps narrow or widen.

Right now, I suspect you have a sample width of about 60 to 70 usec and not 10 usec.

The bumps happen when the gate opens and close, so that is why you have two for each sample. On very short delays, the bumps to not recover and look more like one bump.

Try moving the delay pot and you should see the first two bumps move left and right. If you adjust the sample width, you should see the first two bumps come closer to each other or separate.



Reg

[exciter]

upside down??
i cant see any invert buttons here.
its an old hameg 312 dont know which rev.
have just a +/- Button, but its not an invert...
yes with R46 i can change width of both, main and secondary.
in according to Fig.6 i thought, that the space which i have marked with 10us between the main pulse, and the first bump is the main sample delay.

[Reg]

Post a pic of your scope's controls.

Now, when you adjust R 46, you should see a change in distance between the first two bumps.

The area you marked xxx on your pic is the secondary delay.

Getting back to the pulse width, when you adjust R 46, you should see the distance between the first and second bump change as well as the distance between the 3rd and 4th bump. If you reduce R46, the distance between the first two bumps should narrow.

The area you have marked 10 usec is not the pulse width, but just the width of the first bump. So, that is not the pulse width.

Reg

[exciter]

i mean its the main sample delay.
picture:

[Reg]

Here is your pic with my evaluation of what is what.

[exciter]

"For starters, I would try to get the main delay down as short as possible. I would start out with a 100 usec pulse length, a 10 usec sample time and a second sample at a couple of hundred usecs later than the main sample."

Okay this big pulse should be my pulse length, which i can calibrate with R2/R3.
I have set it to 50~75us.
You said 10usec sample time, dont you mean the sample delay????
where should the main delay be, if not there, where i added the 10usec???

[Reg]

Hi exciter,

It is hard to tell, but does you scope have banana plug connectors? Also, do you have three different connectors being used? If so, why?

I see a red connector plugged in. What does this do? I also see a plug going into the 1m input. What does this do?

It appears you have a connector on the vert input. What does this do?

I suspect you don't need all three.

If you do not have anything connected to the vert input, then try switching the other two leads and see what happens.

Reg

[exciter]

Hi Reg.
Could be also look like in this picture. I plugged my black Ground wire there because if im using my Oscilloscop probe, i use an extra ground.

[Reg]

Exciter,

We need to make sure the scope pics are correct before trying to adjust things. So, we need to get the scope setup right.

Your pic of TP 4 should more like the pics in the HH article. We need to get that to happen first. Once we do that, we can continue

Now, I just saw your latest pic and you should only use one ground. In the latest pic, it appears you are doing that. So, now, try switching the two leads and see if your pic doesn't invert.

Reg

[Reg]

Hi Exciter,

It appears you are using two plain insulated wires for your scope leads. Is this correct? If so, connect the scope ground lead to the pc board ground connection. The scope input then is used to look at TP 4.

Now, if you are using plain wires and not a scope probe, then this is why you probably are having trouble getting your scope to stabilize or sync correctly.

Reg

[exciter]

okay this worked.
picture: