Have a Bendix m-112 im trying to do my first alignment on. Have a signal generator and a VOM. Chart says to hook output meter across voice coil. Output meter? Will my vom work for this and if so what setting do i use? Voice coil? On the speaker itself? I have no isolation transformer. Can someone lead me and tell me what im suppose to hear, see, and hopefully not feel. Have always just tweeked screws for best performance but would like to understand and be a little more professional than that.
Jack

you could probably use VOM AC setting across the speaker checking for peak voltage in that application. I just do it by ear. mostly without any device just listening to radio stations at opposite ends of the dial for best sound. there are many voltage checks including across AVC resistor if you want to do it that way. meter checks will tell you more about how well each section is working or not. I am sure that there is plenty of internet reference material on the subject

Thanks tubeAMP, hope all you pros will share your experience on this, teach me and the other newbs a few things.

Jack,

Is there a schematic for your radio online, somewhere? Can you point us that way? ( NA doesn't list this exact model number.) Are the alignment instructions online?

What sort of VOM do you have? Is it an analog meter? What low level DC and AC ranges does it have? What is the sensitivity on the DC ranges? ( Usually expressed as ohms per volt.)

Is your signal generator checked-out and working? Did the check-out include safety? Does it have a three prong AC line plug that grounds it?

Sorry to have so many questions, but the answers may lead to better advice.

NA have a Rider schematic for a Bendix 112. If this is a similar radio, the set is an AC/DC AA5 with 50L6, etc.

This schematic shows the on/off switch wired to assure that there will be line AC voltage on the set's B- bus. One side of the AC line is switched to the B- bus, while the other end of the heater string and the rectifier plate are tied directly to the other side of the AC line.

If the radio is indeed wired this way, it's bad news on the service bench. An isolation transformer is a really good idea.

Ted

Hey Ted, thanks for response. Riders 18-7. 50L6 is correct. Anolog meter, DC 20K ohms/V. AC 9Kohms/V. I probably need to learn what that means in relationship to troubleshooting radios huh. The radio is actually working pretty good, im mainly trying to get familiar with the sg operation for when i really need it. Looks like its time to get an isolation transformer. What do i need to be looking for?
Jack

Output measurement -- if you're measuring across the speaker voice coil, I suppose any meter will do, capable of measuring AC voltage. Adjust for loudest tone, or measure for highest voltage, meaning the same thing except the meter might be a tad more accurate. Some radios ask you to measure a DC voltage, generally around the AVC line. For this you should go with a high-impedance meter, such as a VTVM or good digital meter. I personally use a scope -- one of the few things I actually use the scope for.

Yes, with most simple radios it's easy enough to tweak for strongest signal and leave it there. But sometimes things just don't seem to line up, and "using the instruments" can help. It will also uncover such things as bad IF's, and also realize that on some fancier radios, not all IF adjustments are for tweaking. Many wonderbar car radios have one IF adjustment you set to MINIMUM instead of maximum.

I agree with the line isolation transformer; I personally hate working on AA5's for that reason -- but if you use the isolation, and understand what you're doing, it's really not that hard to work on them.

Jack

Is there some reason you aren't aligning by measuring AVC voltage? AVC goes negative with alignment. That way you don't have to listen to a loud tone from the speaker.

http://www.nostalgiaair.org/PagesByMode ... 002321.pdf

Thanks Gary for the input. Hey Norm, Since ive never done this before i was going by what the alignment chart says about hooking a meter across the voice coil and thats what the initial ???s were about. I am looking for input from you veterans so i can get a little more familiar with this. Thanks Jack