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

Hi,

It sounds like you no longer have automatic gain control (AGC)action.
The AGC circuit should provide a negative voltage to the grids of the IF
amplifier tubes, to reduce their gain with strong signals.
Lack of AGC would lead to "blocking" which is as you describe.

73,
Ed Knobloch



Steven Burrows wrote:
snip
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

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

What would cause a lack of AGC action? I was operating the radios with the
AVC off when I noted the apparent RF gain saturation. Would a lack of AGC
be a result of the radios being misalligned, or is it symptomatic of a
component failure?
"Edward Knobloch" wrote in message
news:kcJZe.9419$gi4.6305@trndny04...
Hi,

It sounds like you no longer have automatic gain control (AGC)action.
The AGC circuit should provide a negative voltage to the grids of the IF
amplifier tubes, to reduce their gain with strong signals.
Lack of AGC would lead to "blocking" which is as you describe.

73,
Ed Knobloch



Steven Burrows wrote:
snip
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

"Steven Burrows" wrote in message
news:MgKZe.27142$8q.19130@lakeread01...
What would cause a lack of AGC action? I was operating the
radios with the
AVC off when I noted the apparent RF gain saturation. Would a
lack of AGC
be a result of the radios being misalligned, or is it
symptomatic of a
component failure?

The key words are " I was operating the radios with the
AVC off when I noted the apparent RF gain saturation.

Leanne

Hi,

If you were operating the radios with the AGC off,
that would cause the blocking action at the higher gain settings
which you noted.

The S-40 radios are intended to be used with AGC switch "on" in A.M. mode.

AGC "off" is intended to be used only with the BFO on (for c.w. reception).
This is because the beat frequency oscillator would otherwise
be detected by the AGC circuit as if it was a very strong received
carrier, which would cause an unwanted constant reduction in the
receiver gain by AGC action during c.w. reception.

73,
Ed Knobloch



getSteven Burrows wrote:

What would cause a lack of AGC action? I was operating the radios with the
AVC off when I noted the apparent RF gain saturation. Would a lack of AGC
be a result of the radios being misalligned, or is it symptomatic of a
component failure?
"Edward Knobloch" wrote in message
news:kcJZe.9419$gi4.6305@trndny04...

Hi,

It sounds like you no longer have automatic gain control (AGC)action.
The AGC circuit should provide a negative voltage to the grids of the IF
amplifier tubes, to reduce their gain with strong signals.
Lack of AGC would lead to "blocking" which is as you describe.

73,
Ed Knobloch



Steven Burrows wrote:
snip

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

Read the instruction manual carefully. A careful reading should tell you
how the avc switch works, and your description sounds perfectly normal if
the avc switch is off.

Very few transformers need replacing. They are simply wire on an iron core
and unless the wires corrode due to moisture, they will last much longer
than the owner. It would be difficult to find transformers that are exact
match for the original.

Colin K7FM