[Hammarlund] HQ140 - really *LOW* sensitivity

[Richard Knoppow]

----- Original Message ----- 
From: <na2x at yahoo.com>
To: <hammarlund at mailman.qth.net>
Sent: Tuesday, January 15, 2013 11:54 AM
Subject: [Hammarlund] HQ140 - really *LOW* sensitivity


I'm working on a HQ-140X trying to get it into working 
order. I've spent many hours trying to figure out what's 
going on with it but so far, no luck.

The radio basically works, but the sensitivity is really low 
on it. Yes, the sensitivity control is at max. The only AM 
station I can pick up is our local 50KW clear channel 
station. It comes in about S4 on the meter. Other than being 
weak, it sounds OK.

Here's the puzzle. Quite by accident, I had the aluminum 
cover off the variable tuning capacitors on top of the 
chassis. I noticed when I bring my hand near the antenna 
trimmer cap, the sensitivity comes way up. If I touch the 
trimmer cap, the radio really comes alive to the point where 
I think it's working as it should (if it would only stay 
like that). The local 50KW station almost pegs the S meter.

To me it sounds like something in the antenna input 
circuitry but I've traced the wires to the switch and that 
area, checked the antenna coils for continuity, checked 
grounds, and haven't found anything. Should I continue 
looking in this area or does anyone have any other 
suggestions?

I'm just about ready to through in the towel, I've spent way 
too much time on it. I really don't want to give up on this 
receiver, it's a nice one and it's in really good shape.

Thanks,
Bob NA2X

   The antenna trimmer is right at the grid of the first RF 
tube.  If you get a signal by getting close to it it means 
the everything following is working OK. If the low 
sensitivity is on all bands something has happened at the 
band switch. I suggest cleaning it very thoroughly and 
examining it for any mechanical damage or loose or 
unsoldered wires.  You can also check for loose contacts by 
pushing on them with a toothpick. I would go over the whole 
band switch even though the antenna section is only a couple 
of decks. Certainly clean it thoroughly.


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