Valve Radio Vs Solid State Radio - Page 2

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Re: Valve Radio Vs Solid State Radio



"Joerg"...
Quoted text here. Click to load it


**   Ever heard of AFC  ( automatic frequency control)  ??




...............   Phil



Re: Valve Radio Vs Solid State Radio


Hello Phil,

Quoted text here. Click to load it

ROFL.

Actually when you turn AFC on it gets even worse. Then the tuner hangs
on to a strong station for more than 400kHz. In my opinion AFC was a
kludge, probably invented because some folks couldn't figure out how to
design a stable oscillator.

Regards, Joerg

http://www.analogconsultants.com

Re: Valve Radio Vs Solid State Radio



"Joerg"
Quoted text here. Click to load it

** The point is that AFC creates an effect like that of a very broad IF when
this is not the case.


Quoted text here. Click to load it


**  No -  the AFC is counteracting your attempts to re-tune the radio  -  it
needs to be disabled when tuning.

 In any case - a broad IF is *required* for low distortion on the FM band -
plus you will not hear adjacent channel signals along with the wanted one
since the FM "capture effect" prevents that.


Quoted text here. Click to load it


**  So the dial says -  but the local oscillator frequency has been pulled
in the opposite direction to the tuning dial.


Quoted text here. Click to load it


** Variable VHF oscillators stable to within  +/- 20 kHz  over the room temp
plus internal gear temp range are indeed a design challenge, especially in
the case of varicap ( non tuning gang) tuners.  However, AFC compensates for
oscillator drift and mistuning for very little cost.

Modern FM tuners ( since the 1980s) have their tuning frequencies derived
from a crystal time base so drift is eliminated.



..........   Phil



Re: Valve Radio Vs Solid State Radio


Hello Phil,

Quoted text here. Click to load it

Yes, I see what you mean. But you would notice that because there would
be a "hysteresis" in frequency, you'd have to get closer to the station
frequency for it it pop in versus where you lost it.

Quoted text here. Click to load it

I never use AFC. In radios where it can't be disabled I usually go in
there and do a little surgery.

Quoted text here. Click to load it

Not if you want to listen to a weak station next to a strong one. A high
IP front end and a good crystal filter is the ticket here. My old
Kenwood did great but anything after that was, well, close to junk in
performance.

Quoted text here. Click to load it

No, I don't use AFC.

Quoted text here. Click to load it

Little cost but often at the expense of not being able to listen to a
weak station on the next frequency.

Quoted text here. Click to load it

This is one of those. But the lack of a reasonable IF filter does it in.

Regards, Joerg

http://www.analogconsultants.com

Re: Valve Radio Vs Solid State Radio



"Joerg"
Phil  Allison
Quoted text here. Click to load it

 **  That is correct.  One receiver I saw ( Goodmans 110 from the late
1970s ) allowed you to move the dial pointer half way along the band before
the AFC finally let go and the frequency snapped back to match to pointer
!!!!!


Quoted text here. Click to load it


**  A very rare thing for anyone living in a major Australian city.

   I understand Yanks are far more keen on that hobby activity.


Quoted text here. Click to load it


 **   Errr,   IP  =   "intercept point"   ??

Short for:  "third order, intercept point"  ??

Jargon I can handle,  but abbreviated acronyms for jargon is bit much.



Quoted text here. Click to load it


**   Shame how that contradicts your comment above.


Quoted text here. Click to load it


**  I see you like to ignore facts and post red-herrings.

   (  Nearly all radios have AFC disable switches )



Quoted text here. Click to load it


**  I just checked my hi-fi FM tuner ( digital tuning) and found that with a
strong signal I can offset the frequency by +/- 200 kHz before the signal
deteriorates to a garbled noise.

This suggests that the IF filter is  400 kHz wide at the -60 dB points.

The IF filter for a hi-fi tuner is likely to be about 200 kHz wide at
he  -3dB points.

I reckon that is OK performance.





..............    Phil





Re: Valve Radio Vs Solid State Radio


Hello Phil,

Quoted text here. Click to load it

Oh man, I haven't seen AFC this bad.

Quoted text here. Click to load it

They are actually not too far away but we have some interesting stations
that are low power (the ones that play the real blue grass country
stuff...). So their signal might be 60dB or more below the mainstream
stations. Unless you live right in the city, which we don't.

Quoted text here. Click to load it

Sorry. Yes, I meant 3rd oder IP.

Quoted text here. Click to load it

Huh? I hope I didn't leave the impression that I advocate AFC. To me it
is and always was a kludge. The guys that designed the tube sets somehow
were able to come up with a stable oscillator, despite the intense temp
changes in these sets. But that doesn't surprise me. Once when I
mentioned the tempco of a cap in a meeting all the young engineers
looked at me with wrinkled foreheads.

Quoted text here. Click to load it

I have seen (and repaired) a lot that didn't. The one I had went under
the knife and after that it no longer featured an AFC.

Heck, I even repaired a TV set once that had an "automatic station
finder" that used the AFC principle. No disable switch. It was terrible.
You watch a nice old movie, an airplane flies through the path and the
set whooshes to some moronic show on the next channel.

Quoted text here. Click to load it

200kHz at 3dB is a bit wide but ok. 400kHz at 60dB would be quite
stunning. They must have had good engineers (or a decent enough
cost-of-goods budget). Are you sure it's 60dB down there? That would be
highly unusual for an FM tuner unless it is in the >$1000 class.

Most of them I measured wouldn't reach -60dB anywhere.

Regards, Joerg

http://www.analogconsultants.com

Re: Valve Radio Vs Solid State Radio




Joerg wrote:

Quoted text here. Click to load it

AFC isn't normally needed in a well built tube AM tuner,
especially if they have a temp compensated C in the oscillator circuit.

In FM sets with all tube tuners and ratio detectors,
AFC is easy with the detector DC applied to a 1/2 twin triode
at the input to make a reactance tube, thus a small DC offset change
prevents the oscillator from drifting much, because
little C change is needed to tune a large F change at 100MHz.


Quoted text here. Click to load it

Most old AM/FM receivers did not have and did not need
crystal filters for local stations.

Quoted text here. Click to load it

Tube sets drift a bit without AFC.

Patrick Turner.

Quoted text here. Click to load it


Re: Valve Radio Vs Solid State Radio


Hello Patrick,

Quoted text here. Click to load it

Not much though if their designers were clever and had enough budget.
They used variable caps with dissimilar metals in them that compensated
for temperatur expansion. These old engineers also knew how to gauge the
drift of an inductor and compensate for that with capacitor tempco.

Seriously, I have met young engineers who didn't even know that
capacitors had a temperature coefficient.

The best radio I ever saw was an old (tubed) Drake short wave receiver
whose oscillator barely drifted 100Hz. It doesn't have to be this good
but there should be no problem keeping an FM tuner to within a few kHz
without an AFC.

Regards, Joerg

http://www.analogconsultants.com

Re: Valve Radio Vs Solid State Radio




Joerg wrote:

Quoted text here. Click to load it

AM sets below 1,600 kHz don't drift much with a tempco cap
in series with the oscilator tuning gang section.

But the FM sets drift a bit, but the AFC using detector DC applied
to a triode to vary C on the oscillator LC tank works very well and once
tuned
a set won't drift. Set up right, it can run without a disable switch as it
is in my set,
and once one of two tuning meters indicates strongest limiting and the other

indicates 0VDC as a centre reading for the ratio detector, the set would
stay tuned for years if left on.


Quoted text here. Click to load it

The point of using FM is that tuning does not have to be spot on,
and few kHz off the station F doesn't matter.

Patrick Turner.

Quoted text here. Click to load it


Re: Valve Radio Vs Solid State Radio



Quoted text here. Click to load it



Very handy for FM satellite reception where Doppler shift means that the
frequency appears to move constantly. Both my R-9000 & R-8500 have it & I
wouldn't want either of them without it.

ruff



Re: Valve Radio Vs Solid State Radio



"roughplanet"
Quoted text here. Click to load it


**  Must be low orbit,  ham radio satellites  -  the usual commercial ones
are all geo-stationery.

 I guess you would get about +/- 50 ppm frequency shift or about  +/- 7 kHz
in 144 MHz, worst case.

 BTW

Those two "radios" are Icom wide range jobs.



...........    Phil





Re: Valve Radio Vs Solid State Radio



roughplanet wrote:
Quoted text here. Click to load it
filter"
Quoted text here. Click to load it
latest
station's
hangs on
kludge,
design a
the
& I
Quoted text here. Click to load it
Why is there Doppler shift with FM satellite reception? Are you talking
about satellites that move?


Re: Valve Radio Vs Solid State Radio



 roughplanet wrote:


Quoted text here. Click to load it





Yes.

ruff



Re: Valve Radio Vs Solid State Radio


Hello Ruff,

Quoted text here. Click to load it

Agree. But that is an application where you don't compensate for sloppy
engineering but for something that is happening because of the laws of
physics, where there is nothing other than an AFC that would fix it.

Regards, Joerg

http://www.analogconsultants.com

Re: Valve Radio Vs Solid State Radio




< snip >



Quoted text here. Click to load it



Speaking of AM whatever happened to AM Stereo?



Re: Valve Radio Vs Solid State Radio




Quoted text here. Click to load it

http://ourworld.compuserve.com/homepages/kevtronics/history.htm



Re: Valve Radio Vs Solid State Radio


Hello Kate,

Quoted text here. Click to load it

Living in the US where AM stereo was very popular on car radios all I
can say is that the typical new rig from the store doesn't have AM
stereo. Seems like it's fizzling.

Most AM stations are talk radio or programming to small ethnic groups.
Neither would care much for stereo.

Regards, Joerg

http://www.analogconsultants.com

Re: Valve Radio Vs Solid State Radio


   Most domestic valve radio was build as a lowest
common denominator product where every component
inclusion was argued over. I have an AM Kriesler
stereo unit with Garrard turntable and electrostatic
tweeters I rebuilt in 1990: it was full of out of
tolerance resistors and leaky wax capacitors.

   Possible a larger speaker, a larger case and
class A audio contributes to the sound. It would
typically be a single ended class A output stage
too, likely a pentode stage.

   It's possible to have good sounding valve radio
Patrick Turner has build a modified one and I
think has the schematics on his website.


Re: Valve Radio Vs Solid State Radio



Quoted text here. Click to load it



Not quite what I was talking about. But interesting all the same.

Thanks for writing




Re: Valve Radio Vs Solid State Radio



Quoted text here. Click to load it


Have you had a listen to the Tivoli Audio model 1 ?
not cheap at $300 for a mono am/fm table radio, but it does have a beautiful
sound.  I have this 1.

http://www.tivoliaudio.com/product.php?productid16%4&cat=&page=1

Steve



Site Timeline