[Hallicrafters] SX-28A Issues

[Mike Everette]

The clue here, is that the B plus is at least 100 volts low.

Something is drawing a helluva lot of current.

You have a shorted filter cap; or more than one.  At least one is so leaky it's all but shorted.  You are definitely at risk of burning up the filter choke, in a short time.

Replace the filters.  All of them.  

If you have not recapped the radio, bite the bullet and get out your soldering iron.  If there is a paper cap from the output tube plate(s) to ground, be sure you replace that one because if it shorts, your output transformer will fry.  The Hammond replacement audio transformer costs more than you want to know.

73

Mike
WA4DLF
--------------------------------------------
On Tue, 4/1/14, Richard Knoppow <1oldlens1 at ix.netcom.com> wrote:

 Subject: Re: [Hallicrafters] SX-28A Issues
 To: "Joe Connor" <joeconnor53 at yahoo.com>, "Waldo Magnuson" <magnuson at mac.com>, hallicrafters at mailman.qth.net
 Date: Tuesday, April 1, 2014, 10:55 PM
 
 
 ----- Original Message ----- From: "Joe Connor" <joeconnor53 at yahoo.com>
 To: "Waldo Magnuson" <magnuson at mac.com>;
 <hallicrafters at mailman.qth.net>
 Sent: Tuesday, April 01, 2014 7:04 PM
 Subject: Re: [Hallicrafters] SX-28A Issues
 
 
 How old are the filter caps? Could they be leaking? What you
 did with parallel caps would work if they were open but not
 if they were leaky or shorted.
 
 Joe Connor
 On Tuesday, April 1, 2014 9:59 PM, Waldo Magnuson <magnuson at mac.com>
 wrote:
 
 Hi, My SX-28A was playing okay (after a long rest). Then the
 BCB station went away and the audio became a loud hum. I've
 tried: pulling the 1st audio amplifier (v12, 6SC7), hum
 remains, Substituted both 6V6GT audio output tubes - hum
 still present, paralleled C48 & C49 (power supply output
 caps) and C47 (cathode bypass for 6V6s) - no change, B+
 measures maybe 150v (not schematic 250v). Any suggestions
 welcome.
 > Skip W7WGM
 
     Joe has probably got it. Disconnect the filter
 caps and put others in their places. Even if only one is bad
 replace them both.  The symptoms are typical of bad
 filter caps.
 
 
 --
 Richard Knoppow
 Los Angeles
 WB6KBL
 dickburk at ix.netcom.com
 
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