[Heathkit] HW-16 problem

[Tom NØJMY - AAR7FV]

I'm not sure I understand your description of the problem.  Seems like 
many, if not most, HW-16's exhibit a hum, or hollow feedback noise in 
the speaker when the AF gain is backed away from full clockwise.  I 
think it's due to stray ground loops.  You can try ungrounding the 
shield of the coax at the AF gain pot, but that seldom works for me.

Here's part of a post I made on the subject earlier this year:

"In the end, I cure the problem, rightly or wrongly, by replacing and
changing the value of C87, which which bypasses the control grid of V6B,
the audio power amp half of the 6FH8.  This was originally a .001 uf.
disk cap.  I replaced it with a .01 uf.

I experimented with various values using a capacitor substitution box,
although it and the attendant hook-up wires exacerbate the problem
somewhat themselves.  Generally, the larger the value of the cap the
greater the hum reduction (through about .047 uf. where it was
imperceptible).  However, the gain of the amp started to take a hit
above about .0033.  I settled on .01 as a good compromise, as the
decrease in gain was barely noticeable, and once the jumper wires were
removed and the installation was made permanent, the hum virtually
disappeared.  Maybe a .0068 would have sufficed.

I recapped the power supply prior to this, BTW.  It's possible that this
might be an uncouth "brute force" approach to a problem whose origins
are elsewhere in the rig, but hey, that's what God created us uncouth
brutes for."

As for the low sensitivity, is it on all bands?  First thing I do is 
tighten all the circuit boards screws down real good, and then wiggle 
the tubes around a bit (don't burn yourself).  Lots of times the 
contacts are deformed from people setting the rig upside-down with the 
cabinet off while working on it (eventually the unit gets tipped and a 
tube or two gets knocked out at an angle --  seems to happen most on the 
6HF8).  You may have to clean or reform a contact or two with a dental 
pick or whatever.  Also, another common culprit is the bandswitch.  At 
30+ years it should be cleaned real good with some DeOxit.

GL and keep the list informed.

73,
Tom

----- Original Message ----- 
From: "Cam and Juli Hedrick" <walnutcreek at appstate.net>
To: <heathkit at mailman.qth.net>
Sent: Saturday, August 20, 2005 6:41 PM
Subject: [Heathkit] HW-16 problem


> Sensitivity is down, and I'm hearing an oscillation when I turn the AG 
> gain
> to off at 2 like a clock.  It happening when is warm, what cause this? 
> Boy,
> new tubes in it as well.  Please help me guys.  I built this Hw-16 
> when I
> was 13 years old.
> 73,
> Cam Hedrick
> WA4JKW
>
>
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