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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Tue 02, 2018 5:07 pm 
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Okay, thanks for the suggestions to look into.

That shield over the tuning cap is fastened to chassis with 4 screws. I will add more lock washers to be sure of good contact to chassis.

I forgot to mention that just before Christmas I removed the worn out original power cord and installed a new one with polarized plug. I ran the hot side to the switch / C12. I used a safety cap of .01. I ran the neutral to the power transformer.

The problem I hear is only when tuning into a station, the buzz starts to modulate the station. I removed the shield mentioned above and the audio clears up and sounds good. I could just leave that shield off but that wouldn't be correct. Later today I will add those lock washers and try it again.


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Tue 02, 2018 9:58 pm 
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Okay, now this is getting crazy. I added the lockwashers to all 4 screws and fastened the shield to the chassis. Now on the bench it is playing well. Next I installed the steel bottom cover under the chassis and it still played well.

So at this point I installed the chassis back in the cabinet and fastened everything down. Now the buzz is back when I tune in a station.

The only thing I can figure being different between playing on the bench and being in the cabinet is the proximity of the speaker / voice coil. Could this cause rf or audio interference?


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Tue 02, 2018 10:31 pm 
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It might be time for Mr. Oscilloscope......I'm wondering what other frequencies might be present.

Otherwise, my normal next step is to try and confirm that the behavior is repeatable---in the process---assuming it does not misbehave on the bench--try to make it do so---eg by moving the speaker around, poking things, whatever.

This kind of thing is not fun......

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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Tue 02, 2018 10:44 pm 
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Okay.
A new problem, now the wife is running the Plasma TV & noisy Roku box so I can not do more testing until all of that stuff is turned off.
Do I dare ask her to shut it down. NO.

I will have to wait until later, but I'm thinking maybe one of those 4 long screws holding the chassis into the cabinet may be shorting something inside the chassis? I have seen this happen before on a stereo receiver I took apart!

G.


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Tue 02, 2018 11:27 pm 
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There is a significant difference between buzz & hum. Moving the chassis from one point to another may in fact bring it closer to the source of the interference. Unless there is an electrical arc in the field coil & it still has a field coil speaker, it is an unlikely. Did you try shorting out the antenna?

I am of the opinion that if it is Buzz, it has to be external. I have found power supplies in fridges running LED lights to generate RFI same with LED floodlights; computers, computer modems; wall warts, compact fluorescent lighting, etc. Telephone company here actually found a fridge light wiping out signal. Switch-mode PSU's in general are a curse. and I have even had one put a whistle into a 175KHz IF. Most of the regulatory authorities seem to have lost the plot with RFI suppression. Even test equipment is not immune.

The signal can come from the Utility power supply. As noted several times, mains here has RF riding on it and there are several line filters around the place, doing their best to be rid of it. There have been articles in an electronics Mag here, re inferior utility earth / grounding. That would affect Neutral & arcing of inferior earth stakes is not uncommon. My best earth was a bore casing 120ft long into 80 feet of water. The current main one is in an old creek bed.

I would try a direct couple to chassis of an earth lead. I would support running through the set with an Oscilloscope. An oscillating stage due to a voltage sensitive faulty component can generate "saw tooth" (relaxation oscillator). Make sure that mounting screws cannot touch any component in their path. Faults like this can keep you entertained for hours. I don't have Her indoors as a problem: It's just me: No problem.

Marc


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Thu 04, 2018 2:18 am 
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I agree about tracking down all of the noise sources in our homes these days. Our home is full of them, so I do use other shortwave radios in my collection to check the noise sources and shut them down when possible. They upset both the AM broadcasts here plus the shortwave, we are located in a fringe area for AM reception.

Anyway, back on the Clarion this afternoon, I have removed chassis screws, moved wires around, removed the shield, and moved the speaker all around and nothing helps remove this buzz. But with the radio out of the cabinet and the shield removed the radio again is sounding fine. So I hate to do this but I believe I will send the radio back to the owner minus that troublesome shield over the tuning cap. That seems to be the only reasonable option at this point.


G.


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Thu 04, 2018 5:46 am 
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It is odd that something meant to be a Faraday Cage is doing that. Did you try grounding the chassis. What have you got electrical in proximity of the radio when the chassis is put into the cabinet? That is up down & sideways. A switched off CFL can still create sawtooth.

Marc


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Thu 04, 2018 5:57 pm 
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Today I am running the chassis and speaker out of the cabinet and sitting on the bench. Also that shield is off and the radio is playing well that way.

I have a 100 foot long wire antenna out side hooked up and no ground to the radio. The only ground I have available to try to hook up is through the electrical ground terminal in the wall outlet.

I will be around the bench all day today, I have a Tektronix 2215 analog scope here but I don't have much experience using it. If someone would like to look at the schematic and walk me through some test points with the scope, I would appreciate that.

http://www.nostalgiaair.org/pagesbymodel/690/M0040690.pdf

G.


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Thu 04, 2018 10:57 pm 
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There are two different & intertwined groundings / earthing involved here. The approved Line cap of around 0.01mfd, actually is there to provide a grounding for RF; This is why it should be on Neutral and why I suggest that value & type for shorting out the antenna, to see if its an internal fault. Make sure that there is nothing that can touch that shield. If there are visible trimmers through those holes then then the cover likely behaves as a capacitor. That would mean that it has to be calibrated with it on. In other words it's quite likely to be throwing it off frequency enough to see the fundamentals of the RFI generators being stronger.

Unless the primary of the antenna coil is isolated, grounding the chassis bleeds of any charge from the transformer, or appearing on the chassis and also provides an RF path to ground. As I have noted previously defective Utility earthing is not uncommon but should tend to generate hash.

Marc


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 Post subject: Re: Need help replacing Clarion power supply-Work is Finishe
PostPosted: Jan Fri 05, 2018 6:04 pm 
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Thanks to everyone for the suggestions to help me get this radio working. Not too bad for one about 88 years old!

I do have it running well now. Yesterday I tried swapping the first RF and Detector tubes around. These are old #24 tubes and that seemed to help. Around 4pm yesterday I was able to hear stations from KFAB Omaha and KMOX St. Louis. This amazes me with its ability to pull these in. I also noted that there is no AVC circuit so stations will change volume somewhat.

The radio is back in the cabinet and all fastened down and playing this morning. Consider this project finished. It will be delivered back to the owner in a few days.

G.


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Sat 06, 2018 12:04 am 
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AVC / AGC really came to the fore with detector tubes with independent diodes & for BC band the Pentagrid. The SW never got AGC unless it was a 6SA7, even then rarely as it destabilised the tubes. Many of the older sets had a Local / DX switch, sometimes a contra potentiometer working with the antenna and cathode type volume control.

With the last one with no AGC that I ended up with, there was no schematic, it had been hacked and the DX switch was missing. What I found (in conjunction with an Oscilloscope) was switching into the antenna a 68pF series cap, gave the best compromise between distortion & a reasonable level of controllable audio output. I also increased the IF Amp bias from-3 to -4.5, to sort out distortion on its Plate detector.

Good that you now have it sorted.

Marc


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Sat 06, 2018 2:56 am 
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Yes this radio did come with the Antenna Local / Distant switch. This works very well to cut down strong local stations. I am in a fringe area so most of the time I can leave it in the Distant position.

G.


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 Post subject: Re: Need help replacing Clarion power supply-Work Continues
PostPosted: Jan Sat 06, 2018 5:34 am 
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I am in a different position in respect of AM signal. I have a HPON, one Commercial at 2KW at 11Km, Federal (ABC) at 10KW at 8Km, as the Crow flies and others within a circle of 50KM & 100Km. This does give a better idea of how the set behaves each end of the dial & with different signal strengths. That is why, faced with missing information, I could determine practically the 68pF cap as the most suitable for the set.

Marc


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