How does that meter work?
 

I opened the meter of an Hallicrafters SX-117 to mechanically adjust the zero.
Once open, the meter appeared to be of the moving iron type, that is with no
moving coil. But I was surprised to see that that meter has no spiral torsion
springs either; I can only see a metal (?) dish mounted on the axis, part of
which lies inside a rather flat coil.

With no spring, I cannot understand what forces the needle to stay at zero scale
in absence of current. Therefore I cannot figure out what I should do to adjust
the zero.

The HT-44 as well as the EICO 723 use the same type of meter. Dumping is poor,
and the needle keeps banging for a while when you apply a DC current.

73

Tony I0JX

How does that meter work?
 

Sorry for the OT. I made a mistake, and posted the mesage on the wrong
newsgroup.

Tony I0JX

How does that meter work?
 

On Fri, 8 Dec 2006 21:11:44 +0100, "Antonio Vernucci"
wrote:

I opened the meter of an Hallicrafters SX-117 to mechanically adjust the zero.
Once open, the meter appeared to be of the moving iron type, that is with no
moving coil. But I was surprised to see that that meter has no spiral torsion
springs either; I can only see a metal (?) dish mounted on the axis, part of
which lies inside a rather flat coil.

Hi Tony,

Consult paragraph 5-5:
http://www.rigpix.com/hallicrafter/sx117_manual.pdf

73's
Richard Clark, KB7QHC

How does that meter work?
 

Consult paragraph 5-5:
http://www.rigpix.com/hallicrafter/sx117_manual.pdf

73's
Richard Clark, KB7QHC

Dick,

you read my question too quckly. I was not referring to the electrical
adjustment (there is a potentiometer just for that) but to the mechanical
adjustment.

In a properly maintained radio, the meter should stay at zero even when the
radio is off. That is the reason for the mechanical adustment.

73

Tony I0JX

How does that meter work?
 

On Fri, 8 Dec 2006 22:19:15 +0100, "Antonio Vernucci"
wrote:

you read my question too quckly. I was not referring to the electrical
adjustment (there is a potentiometer just for that) but to the mechanical
adjustment.

Hi Tony,

From paragraph 5-5 "The Meter Zero control may be found directly under
the rear of the meter housing."

73's
Richard Clark, KB7QHC

How does that meter work?
 

Hi Tony,

From paragraph 5-5 "The Meter Zero control may be found directly under
the rear of the meter housing."

73's
Richard Clark, KB7QHC

Again Dick, I have adjusted that control many times and any SX-117 owner knows
that that contriol exists.

I am instead trying to adjust the mechanical zero which has nothing to do with
the control under the rear of the meter housing. Do you appreciate the
difference?

Tony I0JX

How does that meter work?
 

On Sat, 9 Dec 2006 10:49:08 +0100, "Antonio Vernucci"
wrote:

Do you appreciate the difference?

Hi Tony,

Nope.

The meter is always in a condition where current is flowing given that
it shares the cathode load. Paragraph 5-5 says quite clearly how to
set zero for a zero signal condition. Basically, the design reveals
an admission that there is no "zero" in the first place (merely a
minimum).

Aside from that, there is no need to be concerned about a meter
reading for a receiver that is turned off. In short, any attempt to
force a mechanical zero would be negated by the "electrical zero" set
and S-9 calibration.

73's
Richard Clark, KB7QHC

How does that meter work?
 

Aside from that, there is no need to be concerned about a meter
reading for a receiver that is turned off. In short, any attempt to
force a mechanical zero would be negated by the "electrical zero" set
and S-9 calibration.

Yes, I agree that is in principle there is no need to be concerned about a meter
reading for a receiver that is turned off. But I am instead concerned about
that, because I like to have all my equipment in perfect order, and a meter that
does not stay on its zero when the radio is turned off is something that I
dislike and anyway wish to fix.

If I would not have had such requirement, I would not have put the question
because it is fairly evident that, when the radio is on, the zero can be
adjusted by means of the control indicated in the manual. All old receivers have
a zero control for the S-meter.

Moreover, the same problem anyway occurs for the RF output meter of the matching
transmitter (Hallicrafters HT44), which is of the same type. But in the HT44
there is no electrical zero adjustment control, so the only way of zeroing the
meter is to open it and adjusting it mechanically.

By the way, in the meantime I have found the way of zeroing the meter, so it is
no longer an issue.

73

Tony I0JX

How does that meter work?
 

"Antonio Vernucci" wrote in message
...
Aside from that, there is no need to be concerned about a meter
reading for a receiver that is turned off. In short, any attempt to
force a mechanical zero would be negated by the "electrical zero" set
and S-9 calibration.

Yes, I agree that is in principle there is no need to be concerned about a
meter reading for a receiver that is turned off. But I am instead
concerned about that, because I like to have all my equipment in perfect
order, and a meter that does not stay on its zero when the radio is turned
off is something that I dislike and anyway wish to fix.

If I would not have had such requirement, I would not have put the
question because it is fairly evident that, when the radio is on, the zero
can be adjusted by means of the control indicated in the manual. All old
receivers have a zero control for the S-meter.

Moreover, the same problem anyway occurs for the RF output meter of the
matching transmitter (Hallicrafters HT44), which is of the same type. But
in the HT44 there is no electrical zero adjustment control, so the only
way of zeroing the meter is to open it and adjusting it mechanically.

By the way, in the meantime I have found the way of zeroing the meter, so
it is no longer an issue.

73

Tony I0JX

A lot of meters dont "zero" on purpose. This area of the meter is inherently
inaccurate so they are biased off of this point either electrically,
mechanicanically or even magnetically on purpose. Forcing these meters to do
otherwise isnt always making them"right". Unless there is some indication
that there is an inaccuracy with the meter and zeroing will help it is best
left alone. For example I have a linear scale capcitance meter that must
be"zeroed" at about 2pf for it to be accurate on the rest of the scale.
Perhaps one day I will solve this problem by replacing the 50uA meter
movement with a digital meter but it has served me well for 30 years so I
think I will leave it "as is" for now. I guess I could make it "zero" on
power off by applying a bias voltage to the meter when it is on to slightly
move the meter off the peg but attempts to do this have shown that it would
significantly complicate the circuitry and comprimise accuracy.

Jimmie

How does that meter work?
 

"Jimmie D" wrote in message
...

"Antonio Vernucci" wrote in message
...
Aside from that, there is no need to be concerned about a meter
reading for a receiver that is turned off. In short, any attempt to
force a mechanical zero would be negated by the "electrical zero" set
and S-9 calibration.

Yes, I agree that is in principle there is no need to be concerned about
a meter reading for a receiver that is turned off. But I am instead
concerned about that, because I like to have all my equipment in perfect
order, and a meter that does not stay on its zero when the radio is
turned off is something that I dislike and anyway wish to fix.

If I would not have had such requirement, I would not have put the
question because it is fairly evident that, when the radio is on, the
zero can be adjusted by means of the control indicated in the manual. All
old receivers have a zero control for the S-meter.

Moreover, the same problem anyway occurs for the RF output meter of the
matching transmitter (Hallicrafters HT44), which is of the same type. But
in the HT44 there is no electrical zero adjustment control, so the only
way of zeroing the meter is to open it and adjusting it mechanically.

By the way, in the meantime I have found the way of zeroing the meter, so
it is no longer an issue.

73

Tony I0JX

A lot of meters dont "zero" on purpose. This area of the meter is
inherently inaccurate so they are biased off of this point either
electrically, mechanicanically or even magnetically on purpose. Forcing
these meters to do otherwise isnt always making them"right". Unless there
is some indication that there is an inaccuracy with the meter and zeroing
will help it is best left alone. For example I have a linear scale
capcitance meter that must be"zeroed" at about 2pf for it to be accurate
on the rest of the scale. Perhaps one day I will solve this problem by
replacing the 50uA meter movement with a digital meter but it has served
me well for 30 years so I think I will leave it "as is" for now. I guess I
could make it "zero" on power off by applying a bias voltage to the meter
when it is on to slightly move the meter off the peg but attempts to do
this have shown that it would significantly complicate the circuitry and
comprimise accuracy.

Jimmie

I hope Antonio never comes accross a device with a bolometer. It would make
his life miserable.