www.geocities.com/wa2ise/radios/12ba7.html

Souping up ferrite core antennas.
cuhulin

wrote:
www.geocities.com/wa2ise/radios/12ba7.html

Souping up ferrite core antennas.
cuhulin

Any one know a good source for aa5s in good to excellent shape?

I have never found a mass-produced radio that was properly aligned.A
good first step is to tune the ferrite antenna to the maximum gain. The
oscillator coil is usually the one with a red core. Tune the radio to
about 570 for white noise or a weak station. Then adjust the oscillator
coil for maximum gain. You may have to follow the weak station up or
down the dial as you look for the signal peak. Next find the rf trimmer
and adjust it for maximum gain at 1500. Then go back to the red-marked
oscillator coil and readjust it for peak. It should not need much of an
adjustment. Do this several times until the gain is ok at both 570 and
1500. For dedicated knob-twiddlers you can also ajust the oscillator
trimmer to extend the range to 1700. I have found that careful
alignment so increases the gain that further mods are not necessary.
You will probably have to adjust the dial pointer mechanism to get the
numbers right. No test equipment is necessary but you should have a
proper screwdriver to avoid cracking the coil core.

wrote:
I have never found a mass-produced radio that was properly aligned.A
good first step is to tune the ferrite antenna to the maximum gain. The
oscillator coil is usually the one with a red core. Tune the radio to
about 570 for white noise or a weak station. Then adjust the oscillator
coil for maximum gain. You may have to follow the weak station up or
down the dial as you look for the signal peak. Next find the rf trimmer
and adjust it for maximum gain at 1500. Then go back to the red-marked
oscillator coil and readjust it for peak. It should not need much of an
adjustment. Do this several times until the gain is ok at both 570 and
1500.

Where did you get the idea that these are gain adjustments? They adjust the
FREQUENCY of the local oscillator, and assume that the ferrite antenna is
properly tuned as well. The adjustments you describe do *nothing* to
adjust the ferrite antenna.

--
If John McCain gets the 2008 Republican Presidential nomination,
my vote for President will be a write-in for Jiang Zemin.

Those little gain control and trimmer thingys,all the other little
thingys that have those little slots for screwdrivers.Back in the 1940's
and 1950's,they looked sooooo anxious to be meddeled around with,with my
little screwdrivers! No telling how many radios I messed up because I
didn't know (and I still dont know) what I was doing.Reminds me of my
first love life.
cuhulin

Most of the mass-produced radios lack the RF coil to properly match the
ferrite antenna. As you adjust the oscillator coil you will find a spot
where the gain of the circuit is optimum. You are not adjusting the
ferrite antenna: you are matching the oscillator to wherever the
ferrite is tuned to. This will produce stronger signals. Try it.

wrote:
Most of the mass-produced radios lack the RF coil to properly match the
ferrite antenna. As you adjust the oscillator coil you will find a spot
where the gain of the circuit is optimum. You are not adjusting the
ferrite antenna: you are matching the oscillator to wherever the
ferrite is tuned to. This will produce stronger signals. Try it.


That would do winders for dial accuracy.

craigm wrote:
wrote:
Most of the mass-produced radios lack the RF coil to properly match the
ferrite antenna. As you adjust the oscillator coil you will find a spot
where the gain of the circuit is optimum. You are not adjusting the
ferrite antenna: you are matching the oscillator to wherever the
ferrite is tuned to. This will produce stronger signals. Try it.


That would do winders for dial accuracy.

************************************************** **********************************
Actually, this type of radio doesn't have good dial accuracy out of the
box, so the tuned version is not much different than the original as
long as the tuning device is adjusted.
This adjustment is made to have the oscillator 455 khz higher than
whatever the ferrite is tuned to. Since there is no easy way to adjust
the ferrite, adjust the oscillator coil until it is 455 khz higher than
the antenna (ferrite) coil. You will find a spot where the signals are
the loudest. This is where the correct difference frequency is 455 khz
and the gain is maximum through the IF. For example, if the station you
want to receive is at 600 khz, and the antenna is tuned to 610 khz due
to manufacturing tolerances, the oscillator must be tuned to 1065 khz
to have the correct difference frequency. Since the oscillator is the
only thing that can be adjusted, you adjust it. The IF is happy: all it
wants is a 455 khz signal. The increase in gain is especially
noticeable from 550 to 700. All the radios I have tuned could easily
add the new 1600 to 1700 frequencies. The 455 khz IF coils are quite
stable: I haven"t run into any that needed adjusting.

Promoting alternative energy,bush-style.
www.thinkprogress.org

Cutting back on alternative energy,cutting back on VOA.Do y'all see a
pattern there? I See It.

About a year and a half ago,I read an article in the Clarion Ledger
newspaper www.clarionledger.com about what a hindrance bush is to
businesses in Mississippi,that article is right too.
Just name one,ONE,business endevor bush has ever been sucessful in.
cuhulin