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  #31  
Old 02-05-2010, 02:30 PM
ctc17 ctc17 is offline
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Dave, walk me through the alignment. How fast of a scope do you need? From reading the sams it looks like you start with the marker and null then peak some slugs. Then add the signal generator into the scope and the mixer and adjust the waveform.

I have plenty of sets to practice on. I have a cbs bw that I already tweeked by eye and even though it has a good pix I know its way off.

Im definitely not going to touch this for awhile. Would just like to get the equipment and learn how
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  #32  
Old 02-05-2010, 02:50 PM
ctc17 ctc17 is offline
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Gave Hawkeye a call on the crt, $380 to rebuild it.
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  #33  
Old 02-05-2010, 03:10 PM
DaveWM DaveWM is offline
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any old scope will do, you dont need a fast sweep, in fact since your sweeping the detected signal the scope will prob be looking at 60 cps.


I followed the sams, yes it had me set the traps 1st using a vtvm, then the markers on the curve. The vtvm was wierd is said set for a min reading, but that was odd since it seemed backwards that is the it worked better when set for a max, of course maybe I had it reading a min neg which would have been the highest pos, the the lowest neg. I got confused on that part.

the other thing is how to inject the signal, here I followed the instructions, found a old osc tube, cut a grid pin off (hated doing that) used a tube shield wrapped with some paper to isloate from the tuner built in shield. there was a TP just after the detector (this one used a mutipupose tube, some use a SS diode). this is where I had trouble, since on one of my sets the TP was INSIDE the sheid of the IF coil. I had to remove the shield and use a clip on the TP, it was very critical on placement. The Emerson had a better layout.


dont for get to use an AGC bias, the B&K 415 has 3 adjust bias supplies. just make sure you getting neg at the AGC point. I think I started out with about
-3vdc with respect to ground.

you start the sweep and adj both the RF ouput/sweep/AGC bias all of them until you get the unclipped humps. It takes all 3 and is a real balancing act.

If you clip at all it will give false readings so adj to just the point where clipping stops.

turn on the markers (on the 415 you can turn on several). On my sweep gen there is a phasing adj that lets you center the hump otherwise you may get the end of one and the begin of the other hump.

the Sams should tell you what coil does what, have fun.

I just ended up using the markers for setting the traps rather than the vtvm approach.

When your done, try for grins swapping IF tubes (assuming they are the same of course) and watch how it effects the form. Since gain will always be different you will no doubt see a swap since its almost impossible to the humps to be the exact same size.

If you have analog transmisson on reg stations you may want to touch up the traps by eye if you have interference from adjacent channels.

If you want to see some scope patterns go to my thread on vintage tech on IF alignment.

http://www.videokarma.org/showthread.php?t=246854

Last edited by DaveWM; 02-05-2010 at 03:14 PM.
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  #34  
Old 02-05-2010, 04:12 PM
ctc17 ctc17 is offline
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The sams talks about using a signal generator and feeding it into the horizontal of the scope as well as the set. Where does that come in? or does the bk do that?
You cut the grid pin off to killl the osc?

I was looking at the factory service manual on that zenith combo we both got and the alignment is totally different from the sams. They say put the tuner between two channels to kill the osc. (if i can remember ill take that book and photocopy it for you, i think you would enjoy it)

Last edited by ctc17; 02-05-2010 at 04:17 PM.
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  #35  
Old 02-05-2010, 04:27 PM
DaveWM DaveWM is offline
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Quote:
Originally Posted by ctc17 View Post
The sams talks about using a signal generator and feeding it into the horizontal of the scope as well as the set. Where does that come in? or does the bk do that?
You cut the grid pin off to killl the osc?

I was looking at the factory service manual on that zenith combo we both got and the alignment is totally different from the sams. They say put the tuner between two channels to kill the osc. (if i can remember ill take that book and photocopy it for you, i think you would enjoy it)
The B&K does that it has a horz scope out but I dont really think its an issue.


My scope does not have a horz drive just a source for triggers. If your scope has a horz drive input then you can prob reverse the sweep direction, and get a mirror image. On mine the wave pattern was reversed from the direction shown on the B&K and I had no way to correct it. You just have to remember that, easy to tell by flipping the markers on and off. on mine the low side was on the right, while on the B&K is shown on the left.

Guess that makes since if the osc coil is shorted or open mid channel. Better than destroying a tube for sure.

Buddy of mine told me to install a ferrite bead at the end of my coax feed that attaches to the tube shield. I got one of those you find on some computer or VHS tape AC power leads, the kind that clips on.

also note if there is any resistors put in series with the TP's
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