On 9/25/05 7:00 PM, in article QDIZe.27130$8q.1230@lakeread01, "Steven
Burrows" wrote:

I am resoring a pair of Hallicrafters S-40B recieivers. I started fiddling
with these radios about ten months ago. Initially, I just recapped one and
cleaned it up to give my father as a Christmas gift. I worked OK, but was
seriously in need of reallignment. The second S-40B I was planning on
rebuilding for myself.

When I tried to reallign my father's radio, I found that it would not
reallign on several bands. This problem, in addition to the poor condition
of my own, led me to decide on a complete rebuild of both radios from the
ground up (all new caps, resistors, and transformers). I worked off of
schematics for the S-40B that I downloaded off of the BAMA web archive.

Recently, I got both chassis ready to try out. They both worked ok, but I
noticed a new problem on both radios that I didn't see on the first
restoration (new caps only). When I turn the RF gain pot up beyond
approximately 66% of full rotation clockwise, the radio sensitivity drops
significantly and no stations or normal static can be heard. When I back off
on the gain control, the radio returns to normal. I am guessing that this
sympton (observed on bot radios) is from RF amplifier overload. Is this
behavior normal for a tube radio, and is there a fix? These are the first
boatanchors that I have ever tried to work on, so all of this is a new
experience to me. In all cases, I had the radio hooked up to a 100 ft.
random longwire antenna.

If this behaviour is a symptom on a goof-up on my part in rewiring the sets,
I would appreciate some advice on how to fix the problem.

Steve Burrows




The "RF gain" control really is not just RF gain. It is RF and IF gain.

With the sensitivity pot set to highest gain AND AVC on, the receiver won't
overload except on very strong (local) signals. Normally no overload will
be perceived.

If the AVC is off, the receiver will overload about as you describe.

Since the receiver does not have a product detector, for CW and SSB the AVC
will be off and sensitivity will be set to avoid overload. For AM signals
use AVC on and full sensitivity unless overload is discerned, then reduce
sensitivity.

Don