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 Post subject: Heathkit RF signal generator - Internal Arcing
PostPosted: Jun Mon 23, 2003 2:02 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 142
Location: Montclair, CA USA
I am fairly new to repairig radios, but do have an electronics background. <P>I purchased a Heathkit RF signal generator at the SCARS (So Cal Antique Radio) swap yesterday. <P>When I plug it in, it lights up, but has no output. When I switch to the higher frequency setting, I hear internal arcing.<P>I opened the unit and can see that the arcing is between the plates of the dual gang capacitor. The arcing is occurring on both gang units of the cap. I was thinking that maybe a bypass cap was shorted letting excessive voltage get to the cap, but since it is happing to both sides, this is unlikely.<P>The unit has two tubes (6C4 and 12AU7) which both test good.<P>I unsoldered a wire from the selenium rectifier - performed a diode test - the rectifier appear good to me(open one direction and 2v drop in the other).<P>There seems to be no model number on the generator. <P>1) How do a find a schematic?<P>2) What could be causing the arcing? <P>------------------<BR>Thanks - <BR>JohnS..


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 Post subject: Heathkit RF signal generator - Internal Arcing
PostPosted: Jun Mon 23, 2003 2:19 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1265
Location: Grand Blanc, MI USA
With this class of vintage equipment you will likely save time by replacing all the paper and electrolytic caps first--then proceed with any troubleshooting. Often all the caps will be bad and could cause all types of symptoms. Then again--with kit built equipment there is always the possibility that a mistake was made during assembly.<P>Arcing in the cap plates would suggest dirt is present there, and the best way (after as much physical removal as possible) to clear that is to apply high voltage DC (through a current limiting resistor) and burn the dirt out of there. You need to disconnect the cap to do this and make sure the plates are not bent and touching. If the plates are shorted by dirt or touching, the generator would probably have no output.<P>Other folks may have an idea where to find a schematic, and how to identify the generator you have. I think Heath made several different models.<P>------------------<BR>


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 Post subject: Heathkit RF signal generator - Internal Arcing
PostPosted: Jun Mon 23, 2003 2:32 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 142
Location: Montclair, CA USA
Thanks Chris -<P>The unit is very clean, The filter cap did measure 50uF on each leg. <P>I will take you advice and recap the unit. I do want to look at a schematic first though.<P>------------------<BR>Thanks - <BR>JohnS..


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 Post subject: Heathkit RF signal generator - Internal Arcing
PostPosted: Jun Mon 23, 2003 3:26 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
The SG-8 (1955) has that tube lineup. Photo shows a gray panel with white lettering. The BAMA site probably has a manual for download, for this or a similar model (the earlier SG-6 uses different tubes). <P>There's plate voltage on both halves of the cap, so probably it's just dirt or corrosion that needs to be cleaned out.<P>------------------<BR>


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 Post subject: Heathkit RF signal generator - Internal Arcing
PostPosted: Jun Mon 23, 2003 3:36 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 22625
Location: Somers, CT
Alan beat me to this while was I getting the URL for BAMA:<BR> <A HREF="http://bama.sbc.edu/heath.htm" TARGET=_blank>http://bama.sbc.edu/heath.htm</A> <P>Please describe the physical appearance of the generator, including the paint texture. Heath used the same circuitry in lots of generators, and just changed the boxes to reflect their current test gear styling. The SG-8 did use a 6C4 and 12AU7.<P>The RF oscillator is a multivibrator, the tank coil is across both plates of the 12AU7. B+ is feed to a center tap on each of the band coils. You should be reading between 75 to 85 volts on the 12AU7 depending on the band. If the plate voltages look reasonable, you might suspect either bend plates on the tuning cap, or dirt and dust buildup.<P>Pete, K1ZJH<P>------------------<BR>


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 Post subject: Heathkit RF signal generator - Internal Arcing
PostPosted: Jun Mon 23, 2003 4:44 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 5136
Location: Rochester NY USA
The Heath schematic site is gone, but many of the pages live on. Like this one: <A HREF="http://www.continental.freeserve.co.uk/heath/sg-8.gif" TARGET=_blank>http://www.continental.freeserve.co.uk/heath/sg-8.gif</A> <P>------------------<BR>


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 Post subject: Heathkit RF signal generator - Internal Arcing
PostPosted: Jun Mon 23, 2003 6:12 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 142
Location: Montclair, CA USA
Thanks all -<P>I did not know about the BAMA site. The unit is indeed a SG-8. I down loaded the entire HK manual. <P><P>------------------<BR>Thanks - <BR>JohnS..


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 Post subject: Heathkit RF signal generator - Internal Arcing
PostPosted: Jun Mon 23, 2003 6:47 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 37194
Location: Livermore, CA
Hi<P> Bookmark this.. Someone gave us the Heathkit backup address. Maybe it was Tom<P> <A HREF="http://web.archive.org/web/20020201194744/http://www.circuitarchive.co.uk/heath.htm" TARGET=_blank>http://web.archive.org/web/20020201194744/http://www.circuitarchive.co.uk/heath.htm</A> <P>------------------<BR>Norm


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 Post subject: Heathkit RF signal generator - Internal Arcing
PostPosted: Jun Tue 24, 2003 8:10 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2846
Location: Warwick,RI
Before doing anything else,all power supply and tubular caps need replacing as a matter of procedure,along with a thorough cleaning of all controls and switches in all this vintage test gear.You shuld check all resistors,also as some may have changed in value.<BR>Poor solder joints and some lugs left unsoldered are as common as apple pie in kit instruments,and wiring mistakes are very possible.<BR>Malcolm Leonard<P>------------------<BR>


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