Until fairly recently I didn't use a signal generator for alignment. Signals heard on the air were adequate. Everything from WWV to local AM BC stations. Sometimes I only used background noise. I peaked everything and got pretty good results. Occasionally the unit would break into oscillation and that would confound me. I remember fooling with bypass capacitors, off-peak alignment, swapping tubes, and anything else I could think of. I used to assume crystals were accurate; I didn't learn until much later that it's not so.
These are the ways you learn what is going on. The better the test equipment, the more we rely upon it, sometimes to the detriment of understanding circuit operation. Other times, it shows how some fundamental things really work.
Unless you are dealing with a critical adjustment, listening to the radio as you tweak each trimmer can tell you a lot. Bias adjustments do require a means of measuring the voltage. Often you can play 'adjustment roulette' by assuming the engineers knew what they were doing, and setting all adjustments in the center of their ranges. If nothing else, it makes a decent starting point in most cases.
Learning the hard way actually can be the best way. I'm not advocating these seat of the pants methods, just saying that with some thought they can actually work.
Bob
On Monday, June 6, 2016 11:56 AM, "Ralph Mowery ku4pt@yahoo.com [Amateur-repairs]" <Amateur-repairs@yahoogroups.com> wrote:
If it is one of the newer digital scopes and the time base is accurate enough and if it will read out to the resolution you need you may be able to use it. I am seeing a lot of others saying you can not, but they may be thinking of the older analog scopes.
The computer should be fine to generate the audio if you isolate the output to protect the sound card. There may be some problem adjusting the audio to the correct level, but a few resistors will take care of that if the level is too high.
One of the best bargains in test equipment on ebay is the used HP 8924C service monitor. It is big and weighs about 70 pounds. It will do almost anything you can think of, but be ready to spend about a month of playing with to find out what it will do. The manual that comes with it is useless as the set was sold to work on the old cell phone systems. Look for the 8920 manual and learn how to use it as the 8924c is very similar except for the added cell phone stuff. They can be had for around $ 700. There is a great user group on Yahoo for them.
From: "hitekgearhead@hotmail.com [Amateur-repairs]" <Amateur-repairs@yahoogroups.com>
To: Amateur-repairs@yahoogroups.com
Sent: Monday, June 6, 2016 10:53 AM
Subject: [Amateur-repairs] substitute test equipment
I am starting to go through the alignment on one of my radios and don't have every piece of test equipment listed in the service manual.
So, I wanted to see if I could use the following substitutions.
For the frequency counter & RF voltmeter, couldn't I just use my oscilloscope? I have access to a scope that can internally measure all kinds of parameters including frequency, Vp, Vrms, etc. Any problem with doing that?
Audio signal generator: I have both a program on my computer and an app on my phone that will generate audio tones at adjustable levels. Any problem with that instead of using a dedicated audio generator?
I still need to get my RF signal generator up and running. I have an old wavetek that is a little persnickety...
Thanks,
Albert
KI4ORI
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Posted by: Bob Albert <bob91343@yahoo.com>
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