[Hallicrafters] SX-17 BFO Question

[Richard Knoppow]

----- Original Message ----- 
From: "Joe Connor" <joeconnor53 at yahoo.com>
To: <hallicrafters at mailman.qth.net>
Sent: Sunday, December 22, 2013 8:06 PM
Subject: [Hallicrafters] SX-17 BFO Question


I'm having trouble troubleshooting the BFO in this receiver 
and I need help. Here's the most legible schematic: 
http://bama.edebris.com/manuals/hallicra/sx17/ When I first 
got the receiver, the BFO was loud and strong but it got 
very weak as I went through the recap procedure and it is 
now still very weak.

Here's what I've done: checked the 6J7 tube and tried 
several replacements, replaced the two wax paper caps in the 
BFO compartment, checked the resistors in the BFO 
compartment, tried adjusting the trimmer on the BFO can, 
tested the BFO pot and switch. All the BFO voltages are good 
per the manual.

I'm wondering about C-62, the 10 pf cap that couples the BFO 
to the 6R7, second detector. Is that a possible culprit? The 
manual says that it's mica but it's tubular and about the 
size of a very small resistor. Does that sound right? Can I 
replace it with a silver mica? Since I probably don't have 
10 pf in my parts drawer, does 51 pf sound reasonable? Any 
other ideas?

As always, thank you for your help and guidance.

Joe Connor

     The tubular cap sounds like an early ceramic cap. Many 
of these look like "dog bone" resistors.
     The SX-17 has a BFO injection control, did you check 
that its turned up?  If that is not the problem and you have 
a scope you can use it to check the BFO function.  Its not 
uncommon when doing extensive work like re-capping to 
mis-wire something or to disturb marginal soldering 
somewhere.  Check your work _very_ carefully and poke at the 
wiring to see if there is an old solder joint that no longer 
makes contact.

--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com