TRABEM wrote:

Thanks Paul,

My old Drake C line had a multiple ganged permeability tuned inductor
mechanically coupled to a variable cap.

One of the assemblies tuned the front end, one peaked the driver
stage, etc.

It covered from 1 Mhz to 30 Mhz with a half turn on the front panel
preselector control. Most likely the variable C and L tuned together
maintained a desirable Q across all the bands.

I was hoping for something similar, but have no idea where to get
permeability tuned inductors today.

Regards,

T


Fair Radio used to have some in their catalog, and they were used in
all of the old Delco (and some other brands) car radios of the '60s and
'70s.


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Michael A. Terrell
Central Florida

Michael A. Terrell wrote:

Fair Radio used to have some in their catalog, and they were used in
all of the old Delco (and some other brands) car radios of the '60s and
'70s.

Just about all the radios I've seen with mechanical pushbuttons for
station presets used permeability tuned inductors -- the pushbuttons
each just positioned a ferrite core to a preset depth in a coil. It
wouldn't be difficult to construct one, unless you're mechanically
declined like I am.

Roy Lewallen, W7EL

Roy Lewallen wrote:

Michael A. Terrell wrote:

Fair Radio used to have some in their catalog, and they were used in
all of the old Delco (and some other brands) car radios of the '60s and
'70s.

Just about all the radios I've seen with mechanical pushbuttons for
station presets used permeability tuned inductors


All of the american made radios were, but some cheap imports weren't.

-- the pushbuttons
each just positioned a ferrite core to a preset depth in a coil. It
wouldn't be difficult to construct one, unless you're mechanically
declined like I am.

Roy Lewallen, W7EL


I once told one of the Vice president of marketing at United Video
Cablevision that he was mechanically declined and my boss freaked out.
;-) The VP yelled at him and told him to shut up because it was true,
and he was happy that whenever he had to launch a new channel in the
Cincinnati system that everything was set up and ready for him when he
arrived.


Of course, you could make them as individually tuned coils with a
stepper motor or servo per coil.

--
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Michael A. Terrell
Central Florida

"Michael A. Terrell" ) writes:
TRABEM wrote:

Thanks Paul,

My old Drake C line had a multiple ganged permeability tuned inductor
mechanically coupled to a variable cap.

One of the assemblies tuned the front end, one peaked the driver
stage, etc.

It covered from 1 Mhz to 30 Mhz with a half turn on the front panel
preselector control. Most likely the variable C and L tuned together
maintained a desirable Q across all the bands.

I was hoping for something similar, but have no idea where to get
permeability tuned inductors today.

Regards,

T


Fair Radio used to have some in their catalog, and they were used in
all of the old Delco (and some other brands) car radios of the '60s and
'70s.

I thought it was the norm for car radios to be permeability tuned, right
up to the time synthesizers came along. No manually tuned car radio
that I've looked at had a variable capacitor, with the exception of
a relatively recent one that had a frequency counter for the readout.

Car radios would be the best source of the mechanics, at least for
front end tuning and not oscillator use. Of course, the issue isn't
changing the permeability of a coil, that's easy with a tuning slug,
but making it easy to do that from a front panel control, ie the knob
doesn't move in and out. The pre-synthesized car radios would proved
the mechanism. But you did see the occasional article in the old
days about making up such a mechanism, though those tended to be
for oscillators where there was more fuss because they wanted/hoped
for linear tuning.

Michael VE2BVW

Michael Black wrote:

I thought it was the norm for car radios to be permeability tuned, right
up to the time synthesizers came along. No manually tuned car radio
that I've looked at had a variable capacitor, with the exception of
a relatively recent one that had a frequency counter for the readout.

Car radios would be the best source of the mechanics, at least for
front end tuning and not oscillator use. Of course, the issue isn't
changing the permeability of a coil, that's easy with a tuning slug,
but making it easy to do that from a front panel control, ie the knob
doesn't move in and out. The pre-synthesized car radios would proved
the mechanism. But you did see the occasional article in the old
days about making up such a mechanism, though those tended to be
for oscillators where there was more fuss because they wanted/hoped
for linear tuning.

Michael VE2BVW


Some of the cheap imported car radios used the same plastic cased
variable capacitor with mylar film between the plates that were used in
a six transistor pocket radio. They didn't have a tuned front end and
amp like the US made car radios. They were ok if you only wanted to
listen to a local station but they were very poor quality radios.

I think I would use a variable capacitor and electronically switch
the inductor for different ranges, like the broadband L-C Based VCO in
the telemetry receivers I worked on. Diodes were used to short segments
of the inductor, at the grounded end and the band segment was controlled
by simple logic. Bias on hard to short a tap to ground, and reverse
bias it to prevent it from clipping the RF when its off. They used
discrete +/- 12 or 15 volt switching , but a decent buffer amp would
work and could be driven by CMOS or TTL compatible logic. If the
receiver has any switched DC signals to show which band its on, you
could make it change bands without touching it. You could even sample
the L.O. with a counter circuit and use the output to control the
tuning. If you want to g to extremes, you could add a microprocessor
with lookup tables to drive a stepper motor that can adjust the variable
capacitor(s) for you as you tune the radio.

--
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Michael A. Terrell
Central Florida