#46
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He knows. He was posing it as an example of what happens when you don't have a filter cap.
The outer coating of the CRT should be ground. It allows the CRT itself to act as a filter capacitor for the high voltage. |
#47
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Also IIRC the ad claims it will transmit...It doesn't seem to have the power for anything other than a direct connection and even then was going dark regularly.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#48
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I've been working backwards from the speaker in the troubleshooting. Speaker pops and moves on contact with a 9v battery. AOTrans ohms out ok and there's continuity all the way back to the AOTube sockets but that's where it gets dicey. Filament voltages are OK and the tube is new but there's all sorts of out of spec voltages on the other pins. I was going to get a read on them last night and post but I never got off the couch and YouTube all night!!! |
#49
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#50
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That HV meter looks OK. I haven't seen that model before. Yeah, it could be the capacitor smoothing effect.
A quick and dirty way to check the audio output circuit is to touch the wiper on the volume control with a screwdriver with a finger touching the blade. Don't have the volume control turned down however. You should hear a hum. If this was a hot chassis set you definitely want it plugged into an isolation transformer to do this. You would need a FM modulated 4.5MHz audio signal to inject to trace the signal further up (from the volume control towards the tuner). A oscilloscope could enable you to trace the audio from the tuner toward the volume control. Without those you are left with checking voltages, resistors and tubes, etc. |
Audiokarma |
#51
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I do have a scope and a signal generator. I can give those a try. Maybe Mr. Andersen would know if this is a hot chassis but I do have the hot and neutral blades of the power cord marked so I can be sure it acts as a keyed plug. On the topic of the power cord, it's in terrific condition. Is there anything I can do or a treatment I can apply to help preserve the rubber and keep it from becoming hard and brittle? Thanks Chris |
#52
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It is not a hot chassis. I believe the original cord would by vinyl not rubber.
BTW less expensive and more readily available Slip Plate graphite coating works well on CRTs. |
#53
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[QUOTE=bandersen;3242720]It is not a hot chassis. I believe the original cord would by vinyl not rubber.
BTW less expensive and more readily available Slip Plate graphite coating works well on CRTs.[/QUOTE Great...one less shock hazard! I'll google SP and check price and availability. I've got a Zenith and a Philco Seventeener where the dag is flaking off in big chunks! |
#54
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Also he may be able to get away with a tube AM modulated signal generator...Most tube TV/radio repair grade generators distort the the RF carrier enough to create FM/PM modulation that TV audio systems can detect. I've done this with 2-3 different generators so far.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
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Audiokarma |
#56
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Before you start with IF injection first try audio injection at the first audio stage grid. That knight generator should have an audio output you can use. If the set passes audio from the 1st audio grid decently then IF injection is the next troubleshooting step. If it doesn't pass audio injected at the 1st audio grid then troubleshoot the audio stages and make them work before messing with the audio IF. We can walk you through audio IF injection if you end up needing to do it.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#57
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IE, you should hear some pretty weird stuff when you get it right!
__________________
=^-^= Yasashii yoru ni hitori utau uta. Asu wa kimi to utaou. Yume no tsubasa ni notte. いとおしい人のために |
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Nice loud tone on the FM radio BTW from the Knight
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Audiokarma |
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