Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM radio
works fine, well minimal hash from the buzzer mechanism of the vibrator 12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try in
the way of screening/ wire routing makes little difference. Any ideas before
rejecting the project?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

On Jul 10, 1:26*pm, "N_Cook" wrote:
Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM radio
works fine, well minimal hash from the buzzer mechanism of the vibrator 12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try in
the way of screening/ wire routing makes little difference. Any ideas before
rejecting the project?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse:graffiti.net/

Most mp3 players derive their radio reception from the headphones.
Isolate and bring out that wireto an external aerial and you will be
good for the strong FM stations. Next, get some filtering caps and put
them across the B+ and grounds of your player. Your audio output
ground will need to be shielded properly. Can you make a Faraday box
inside that radio?

Adam Kb2jpd

James Sweet wrote in message
news:aetdk.1248$bn3.1183@trnddc07...

N_Cook wrote:
Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those
keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM
radio
works fine, well minimal hash from the buzzer mechanism of the vibrator
12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and
the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try
in
the way of screening/ wire routing makes little difference. Any ideas
before
rejecting the project?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




There's guys who do this regularly, I don't know the details but
hopefully some of them will reply with details. Undertaking this myself,
I would be inclined to replace the vibrator with solid state internals,
not too difficult and you get a lot of added reliability. I'm a little
confused when you say you're operating the FM receiver off the HV power
supply, are you trying to regulate down from the B+ supplied to the
tubes? If you need isolation, how about one of those little DC-DC
converters? I salvaged one from an old eithernet card for a different
automotive project where I needed isolation.

An option that would avoid modifying the original radio at all is to
use a low power AM transmitter fed by the FM receiver and just stick
that elsewhere.

I've replaced the switches with a 10 turn pot for dial tuning of the FM via
the varicap. The 3V is derived from the 12V which is positive ground which
I'm wondering if that may be part of the problem, grounding the + rail of
the TDA. The audio out buffered through a transistor, I've fed in via a
switch , at the volume control prior to the EL42.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

On Jul 10, 4:14*pm, "N_Cook" wrote:
James Sweet wrote in message

news:aetdk.1248$bn3.1183@trnddc07...







N_Cook wrote:
Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those
keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM
radio
works fine, well minimal hash from the buzzer mechanism of the vibrator
12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and
the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try
in
the way of screening/ wire routing makes little difference. Any ideas
before
rejecting the project?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

There's guys who do this regularly, I don't know the details but
hopefully some of them will reply with details. Undertaking this myself,
I would be inclined to replace the vibrator with solid state internals,
not too difficult and you get a lot of added reliability. I'm a little
confused when you say you're operating the FM receiver off the HV power
supply, are you trying to regulate down from the B+ supplied to the
tubes? If you need isolation, how about one of those little DC-DC
converters? I salvaged one from an old eithernet card for a different
automotive project where I needed isolation.

* An option that would avoid modifying the original radio at all is to
use a low power AM transmitter fed by the FM receiver and just stick
that elsewhere.

I've replaced the switches with a 10 turn pot for dial tuning of the FM via
the varicap. The 3V is derived from the 12V which is positive ground which
I'm wondering if that may be part of the problem, grounding the + rail of
the TDA. The audio out buffered through a transistor, I've fed in via a
switch , at the volume control prior to the EL42.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse:graffiti.net/- Hide quoted text -

- Show quoted text -

YOu need to figure out if the Hash is getting conducted or radiated
into the receiver. It should be posible to put the FM unit into an
aluminum foil shielded compartment and then filter the heck out of the
input voltage.

Bob Hofmann

"hr(bob) " wrote in message
...
On Jul 10, 4:14 pm, "N_Cook" wrote:
James Sweet wrote in message

news:aetdk.1248$bn3.1183@trnddc07...


N_Cook wrote:
Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those
keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM
radio
works fine, well minimal hash from the buzzer mechanism of the vibrator
12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and
the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try
in
the way of screening/ wire routing makes little difference. Any ideas
before
rejecting the project?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

There's guys who do this regularly, I don't know the details but
hopefully some of them will reply with details. Undertaking this myself,
I would be inclined to replace the vibrator with solid state internals,
not too difficult and you get a lot of added reliability. I'm a little
confused when you say you're operating the FM receiver off the HV power
supply, are you trying to regulate down from the B+ supplied to the
tubes? If you need isolation, how about one of those little DC-DC
converters? I salvaged one from an old eithernet card for a different
automotive project where I needed isolation.

An option that would avoid modifying the original radio at all is to
use a low power AM transmitter fed by the FM receiver and just stick
that elsewhere.

I've replaced the switches with a 10 turn pot for dial tuning of the FM via
the varicap. The 3V is derived from the 12V which is positive ground which
I'm wondering if that may be part of the problem, grounding the + rail of
the TDA. The audio out buffered through a transistor, I've fed in via a
switch , at the volume control prior to the EL42.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list
onhttp://home.graffiti.net/diverse:graffiti.net/- Hide quoted text -

- Show quoted text -

YOu need to figure out if the Hash is getting conducted or radiated
into the receiver. It should be posible to put the FM unit into an
aluminum foil shielded compartment and then filter the heck out of the
input voltage.

Bob Hofmann

Yeppers, that's exactly what I was going to suggest. I'll bet that shielding
will significantly reduce the hash. Probably need to use a shielded wire for
the antenna as well.
The vibrator is a nasty source of hash noise, and it might take a lot of
shielding to get it under control. I don't think the positive ground system is
necessarily a show stopper. You'll just have to experiment to get the right
configuration... what and how to shield and where to connect it.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Experience: What you get when you don't get what you want

DaveM wrote:
"hr(bob) " wrote in message
...
On Jul 10, 4:14 pm, "N_Cook" wrote:
James Sweet wrote in message

news:aetdk.1248$bn3.1183@trnddc07...


N_Cook wrote:
Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those
keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM
radio
works fine, well minimal hash from the buzzer mechanism of the vibrator
12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and
the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try
in
the way of screening/ wire routing makes little difference. Any ideas
before
rejecting the project?
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
There's guys who do this regularly, I don't know the details but
hopefully some of them will reply with details. Undertaking this myself,
I would be inclined to replace the vibrator with solid state internals,
not too difficult and you get a lot of added reliability. I'm a little
confused when you say you're operating the FM receiver off the HV power
supply, are you trying to regulate down from the B+ supplied to the
tubes? If you need isolation, how about one of those little DC-DC
converters? I salvaged one from an old eithernet card for a different
automotive project where I needed isolation.
An option that would avoid modifying the original radio at all is to
use a low power AM transmitter fed by the FM receiver and just stick
that elsewhere.
I've replaced the switches with a 10 turn pot for dial tuning of the FM via
the varicap. The 3V is derived from the 12V which is positive ground which
I'm wondering if that may be part of the problem, grounding the + rail of
the TDA. The audio out buffered through a transistor, I've fed in via a
switch , at the volume control prior to the EL42.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list
onhttp://home.graffiti.net/diverse:graffiti.net/- Hide quoted text -

- Show quoted text -

YOu need to figure out if the Hash is getting conducted or radiated
into the receiver. It should be posible to put the FM unit into an
aluminum foil shielded compartment and then filter the heck out of the
input voltage.

Bob Hofmann

Yeppers, that's exactly what I was going to suggest. I'll bet that shielding
will significantly reduce the hash. Probably need to use a shielded wire for
the antenna as well.
The vibrator is a nasty source of hash noise, and it might take a lot of
shielding to get it under control. I don't think the positive ground system is
necessarily a show stopper. You'll just have to experiment to get the right
configuration... what and how to shield and where to connect it.


Or put in a modern little isolated switcher followed by a LM317 linear
regulator. OTOH this sounds like a vintage car and one isn't supposed to
have modern fluff such as FM, let alone gasp integrated circuits in
there ;-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Thu, 10 Jul 2008 18:26:22 +0100, N_Cook wrote:

Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM radio
works fine, well minimal hash from the buzzer mechanism of the vibrator 12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try in
the way of screening/ wire routing makes little difference. Any ideas before
rejecting the project?

My gut feeling is the buzz is getting into the FM through the power supply
- your voltage-reduction circuit isn't filtering it out.

What kind of filtering is on the 12=3v ps?

"N_Cook" wrote in message
...
Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM
radio
works fine, well minimal hash from the buzzer mechanism of the vibrator
12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and
the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try in
the way of screening/ wire routing makes little difference. Any ideas
before
rejecting the project?


As many on this newsgroup know, I'm converting car radios to modern AM/FM
stereo.

The Stereo PCB's are made by Antique Automobile Radio of Palm Harbor,
Florida. They also make solid state vibrators, voltage boosters/inverters,
and they used to make an "FM Module."

The FM Module was a neat little device, in my opinion. It was a very small
PCB with an FM tuner, that used the AM oscillator to tune the FM.
Connections were -- one wire to the LO coil, a wire to the antenna, a wire
to the 12v supply (or a small voltage booster could be added if 6 volts
and/or positive ground), and two wires to the volume control -- where you
would tap in at the top of the control. This module worked very well; you
could tune FM with the tuning knob and even set pushbuttons. You switched
bands by turning the radio off and back on. Aside from the FM tuner, the
radio worked normally.

These modules are no longer available, and it's a complicated story, but
overall its popularity diminished when the stereo PCB's were perfected --
when they were discontinued I was one of only two dealers in the world who
were still offering them.

Now -- as for vibrator hash, you are right -- vibrator power supplies are
very noisy. For this reason, car radios always used shielding to keep the
power supply isolated from the tuner. On some radios there is a metal
partition between the vibrator power supply and the rest of the radio. On
others, the power supply (and often the output tubes) were mounted on the
back of the radio, outside the rest of the casing. On still other models
the power supply and output was mounted on a second chassis beside the radio
itself, sometimes with the speaker mounted to the power unit. But in ALL
cases there was isolation to prevent interference from vibrator noise.

The FM modules seldom had problems with this noise, as they were mounted
near the AM tuner which was already isolated from the power unit. However
to prevent the AM from interfering with the FM, a 6.8uH choke was added to
the AM antenna wire (if the radio didn't have one already). In extreme
cases (rare) a relay was placed at the antenna socket, to disconnect the
antenna from whichever band was not being used. On occasional instances
where the vibrator noise would find its way into the FM, a hash choke in the
DC line would take care of it.

Now -- one place where noise WAS a problem was with Stereo Conversions.
Although the vibrator power supply gets removed entirely, on 6 volt or
positive ground cars a voltage booster/inverter is added. Yes, with earlier
versions THESE were noisy (new ones are better) and they would interfere
with the AM reception. The fix: mount the voltage booster as far away from
the PCB as possible, then install a 1000uF electrolytic at the voltage
booster output, then a choke. Although not specified by AAR, I used a
second electrolytic to make a pi filter -- why not? This eliminated the
noise.

As for using a little FM tuner, does it make the noise when you're using the
batteries? If not, probably a pi filter would do the trick. If this runs
on a lower voltage than 12v, you might try a resistor and a zener, and then
an electrolytic (probably doesn't have to be very big) and maybe even bypass
this with something like a .001. Of course you'll want to mount the
filtering near the power supply, and mount the FM tuner in a place that's
partitioned off.


--
Gary E. Tayman/Tayman Electrical
Collector Car Audio
http://www.taymanelectrical.com

On Jul 10, 1:26*pm, "N_Cook" wrote:
Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM radio
works fine, well minimal hash from the buzzer mechanism of the vibrator 12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try in
the way of screening/ wire routing makes little difference. Any ideas before
rejecting the project?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse:graffiti.net/
_________________
There used to be this FM tuner, back 30-40 years ago when most cars
came only with AM radio standard; FM and/or cassette cost extra. You
would mount this paperback-book sized unit below the dash, hook it
into power and add an antenna to a fender to pick up signal. On the
back was a switch that allowed you to select one of three AM
frequencies to which this FM Tuner's AM transmitter would broadcast
the audio to. You would then turn on the existing factory AM radio
and tune it to the AM frequency that matches that selected on the FM
tuner box. Voila - FM - mono! - but FM for sure! I don't know if
this is still manufactured or if most of them are in wrecking yards or
in peoples' garages gathering dust.

Basically it contained an AM transmitter similar to the FM transmitter
you'd plug a MP3 player into, nowadays, to transmit the MP3's audio
over a selected FM freq, IE 88.7 or 108.1 .

-CC

"Barry OGrady" wrote in message
...
On Thu, 10 Jul 2008 18:26:22 +0100, "N_Cook" wrote:

Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM
radio
works fine, well minimal hash from the buzzer mechanism of the vibrator
12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and
the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try in
the way of screening/ wire routing makes little difference. Any ideas
before
rejecting the project?

New AM/FM car radios are cheap.


This is true, but the OP, and many classic car buffs (most, in fact) do not
want to have a modern radio in the dash. They want the original, or one that
looks exactly like the original.

On Jul 11, 11:32*pm, "Brenda Ann" wrote:
"Barry OGrady" wrote in message

...





On Thu, 10 Jul 2008 18:26:22 +0100, "N_Cook" wrote:

Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM
radio
works fine, well minimal hash from the buzzer mechanism of the vibrator
12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and
the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try in
the way of screening/ wire routing makes little difference. Any ideas
before
rejecting the project?

New AM/FM car radios are cheap.

This is true, but the OP, and many classic car buffs (most, in fact) do not
want to have a modern radio in the dash. They want the original, or one that
looks exactly like the original.- Hide quoted text -

- Show quoted text -
---
How about an MP3 player:
http://wps.com/projects/MP3-system/radio-player.html

Gary Tayman wrote in message
news:JTJdk.1$Cw5.0@trnddc01...

"N_Cook" wrote in message
...
Seemed a neat idea but ...
There is space inside this 1950s dashboard radio for one of those
keyfob/
matchbox size FM radios, this one based on a TDA7088T. The original AM
radio
works fine, well minimal hash from the buzzer mechanism of the vibrator
12V
to HV supply and the FM works fine with a proper linear mains derived HV
unit and the 12V to 3V ps. But try the FM off the original HV supply and
the
hash from the buzzer mechanism makes it unlistenable to. Whatever I try
in
the way of screening/ wire routing makes little difference. Any ideas
before
rejecting the project?


As many on this newsgroup know, I'm converting car radios to modern AM/FM
stereo.

The Stereo PCB's are made by Antique Automobile Radio of Palm Harbor,
Florida. They also make solid state vibrators, voltage
boosters/inverters,
and they used to make an "FM Module."

The FM Module was a neat little device, in my opinion. It was a very
small
PCB with an FM tuner, that used the AM oscillator to tune the FM.
Connections were -- one wire to the LO coil, a wire to the antenna, a wire
to the 12v supply (or a small voltage booster could be added if 6 volts
and/or positive ground), and two wires to the volume control -- where you
would tap in at the top of the control. This module worked very well; you
could tune FM with the tuning knob and even set pushbuttons. You switched
bands by turning the radio off and back on. Aside from the FM tuner, the
radio worked normally.

These modules are no longer available, and it's a complicated story, but
overall its popularity diminished when the stereo PCB's were perfected --
when they were discontinued I was one of only two dealers in the world who
were still offering them.

Now -- as for vibrator hash, you are right -- vibrator power supplies are
very noisy. For this reason, car radios always used shielding to keep the
power supply isolated from the tuner. On some radios there is a metal
partition between the vibrator power supply and the rest of the radio. On
others, the power supply (and often the output tubes) were mounted on the
back of the radio, outside the rest of the casing. On still other models
the power supply and output was mounted on a second chassis beside the
radio
itself, sometimes with the speaker mounted to the power unit. But in ALL
cases there was isolation to prevent interference from vibrator noise.

The FM modules seldom had problems with this noise, as they were mounted
near the AM tuner which was already isolated from the power unit. However
to prevent the AM from interfering with the FM, a 6.8uH choke was added to
the AM antenna wire (if the radio didn't have one already). In extreme
cases (rare) a relay was placed at the antenna socket, to disconnect the
antenna from whichever band was not being used. On occasional instances
where the vibrator noise would find its way into the FM, a hash choke in
the
DC line would take care of it.

Now -- one place where noise WAS a problem was with Stereo Conversions.
Although the vibrator power supply gets removed entirely, on 6 volt or
positive ground cars a voltage booster/inverter is added. Yes, with
earlier
versions THESE were noisy (new ones are better) and they would interfere
with the AM reception. The fix: mount the voltage booster as far away
from
the PCB as possible, then install a 1000uF electrolytic at the voltage
booster output, then a choke. Although not specified by AAR, I used a
second electrolytic to make a pi filter -- why not? This eliminated the
noise.

As for using a little FM tuner, does it make the noise when you're using
the
batteries? If not, probably a pi filter would do the trick. If this runs
on a lower voltage than 12v, you might try a resistor and a zener, and
then
an electrolytic (probably doesn't have to be very big) and maybe even
bypass
this with something like a .001. Of course you'll want to mount the
filtering near the power supply, and mount the FM tuner in a place that's
partitioned off.


--
Gary E. Tayman/Tayman Electrical
Collector Car Audio
http://www.taymanelectrical.com






Upped the 3V rail cap from 100uF to 1000uF and upped the 50 ohm resistor
(replacing the earpiece) to 330 ohm to give more signal and the FM was not
too bad, about equal to the AM. That was as far as I was going. AM/FM switch
and small 10 turn tuning pot knob tucked out of sight under the radio
dashboard mounting frame next to the built in ashtray.
At least with this arrangement, rather than down-converter, there is always
a station on either side of the waveband switch without having to tune into
a spot on the AM dial.

So it works in principle but a few more chokes,screening or something is
required, also the bass is lacking on the FM. I'd replaced the 0.1uF AF out
coupler with 2uF but no noticeable difference. No mention in specsheet about
output audio other than the mW but maybe TDA7088 is designed only for
earphones.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/