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Antique Radio Technical Forum
The Hum From The Speaker

Posted by Edd on 04/14/2009 11:27



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:Thought that you had that dude in a quasi- operational state ?
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:With initial consideration to be given to the probably ok. . . power supply levels. . . . and then in considering the audio portions of the receiver, would you evaluate that portion in the following manner for me.
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: Almost ZERO requirements, in equipment, although I think ? that I remember you gradually adding onto your test equipment cache. Should the following modulated 455 R.F. signal be needed on the follow up.
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:What you need is a . . .on the safe side. . . .600VDC rated . .. coupling capacitor of a .001 ufd value and two test leads with clip ends.
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:Consult your schematic and note the coupling of the sets low level audio from the detector stage via the item #38 which is an .01 ufd cap.
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:Then have power down and lift one end of that cap. . .the easiest one to do. Then connect a clip lead to one of the plates of one of the #41 AF output tubes (50/50 chance of being right here. . ..phasing considerations) and then the other end of that clip lead gets connected to one lead of that aforementioned .001 cap, with its other lead receiving another test leads clip and then the free test lead clip goes to the high side of the volume control where the other cap . . . .just lifted. . .. .was cutting off the incoming radio audio.
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:NOW if you power up and warm up the set with the volume at its minimum, you should then be able to slowly advance the volume control and find yourself with an audio sweep
:oscillator.
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:That being, from the initial acoustical antics of a cricket ( on steroids) on upwards thru the resonant frequency of the speaker cone and then the cabinet resonance ( if so contained within) up to the point where some of the higher frequencies should drive Aunt Murgatriod out of the guest bedroom. . . in a frenzied state of panic shock.
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:Should the oscillation effect not have occurred, then you need to move that plate lead connection clip over to the OTHER 41’s plate connection.
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:Somewhere within that sweep the audio level should approach the most volume that the set will ever produce. . . .thus confirming adequate current and voltage supply being present for your audio circuitry as well as the audio portion being up to par.
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: Some evaluation of the tone control circuitry can even be made at the higher frequencies by the “colorization” of the tone control, upon the produced signal.
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:Next question. . ..after the mod RF sig generator availability will be if you have . . . ..preferably, one of the OLD generation fluorescent desk lamps with 1-2 small tubes and the “all important” OLD generation common metal ballast transformer.
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:(Also, some aquariums top illumination lamps, are of that category as well as “gro lux” plant lamps, kids older style black light lamps, etc.)
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:The new generation CFL lamps with their “electronic ballasts” are LESS than desirable with their sharp banding of switch mode activity within 60-75-120 khz clusters.
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:Standing by. . . ..
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:73's de Edd

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:Thanks for getting back Edd. And everyone else too. I will perform these tasks as soon as the radio is back together again. Knocked off at 10 last night and here it is 3:45 am and I'm back at it. Should be done soon. Couldn't sleep anyway.
This is my nephews first resto job. A few mistakes were made and I believe I have identified all of them and made the necessary corrections. I did however decide to pull the band switch assembly because it is the only thing I haven't thoroughly checked. Found mostly dirt in this area. I am having some trouble making sense of the pinouts on the "OSC. TRANS." as pictured on the schematic. Bottom center of page. It looks as if pin 1 is at the right then pin 4 is the next pin at the top of the coil with the black dot next to it. Then pin 7 (also black dot) and 5 on left side. Pin 3 and 2 appear to be at the bottom of the coil. It also appears that pin 6 is at the top of the back of the coil. Is this view looking down with the chassis upside down or looking down with the chassis right side up? With the chassis upside down and looking down at the osc. trans my pin 6 is at the bottom. Not as pictured at the top. Once again, what's the view? I can't trust the nephews connections so I really need to determine this. Lots of connections between band switch and these coils. "ANT. TRANS." is much easier to read but once again... What is the view on this? Looking up, down etc.?
I really do appreciate the help with this and I know we'll get it figured out. Now! Any advice on how to teach a young man patience? I'm telling him that you just can't rush through one of these things.
Thanks folks,
Johnny



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The way that I am seeing that osc coil terminals, is per the enhancement.
Now, as far as the locational dimensional view, rely upon the sole one sided terminal reference of # 6 at the very bottom. Additionally , use for referencing, the physical presence of the 22k resistor that is shunting terminals #5 and #6.




73's de Edd




:


The Hum From The Speaker 
Johnny 04/11/2009 14:58 
Thomas Dermody 04/12/2009 00:16 
Ed M 04/13/2009 13:28 
Johnny 04/13/2009 19:10 
Thomas Dermody 04/13/2009 21:05 
Lewis L 04/13/2009 21:18 
Edd 04/13/2009 22:43 
Johnny 04/14/2009 07:01 
Edd 04/14/2009 11:27 
Doug H 04/15/2009 11:38 
Johnny 04/15/2009 12:01 
Doug H 04/15/2009 12:40 
Johnny 04/15/2009 17:51 
Johnny 04/15/2009 11:54 
Johnny 04/15/2009 19:58 
Johnny 04/16/2009 02:15 
The Rework Is Done 04/15/2009 23:21 

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