"Nothing40" wrote in message
m...

Hey Brenda Ann,Nice to see you hangin around here. :-)

Thanks, at least we aren't getting 300 idiotic posts a day in here. (yet)

(John Byrns) wrote in message ...
In article ,
(firedome) wrote:

Ok, went back and looked at my interview notes...in late '51 before
Will's father passed away Walter Selsted had apparently developed some
kind of tweeter capable of super high frequencies (I'm not aware of
any details)

That was another Selsted & Smith collaboration, they published an article
on it in the January 1950 issue of "Audio Engineering" magazine.

in addition to the circuit found in RDH3 (Will may have
meant 4, maybe, but I wrote down 3 as that's what he recalled) that
was supposed to have a low distortion of around .35%.

I can't find it in the RDH3, unfortunately it appears that they never
published an article on the "low distortion AM detector", the only thing I
have ever seen published about it is in the RDH4, and that doesn't delve
into its operation.

Selsted contacted L.C. Rayment about SR using the circuit as they had a long
reputation for high quality products back to 1927, and arrangement was
made for S-R to use it.

If that is true, it would explain how S-R came to learn of the circuit, I
had come to the probably mistaken conclusion that it was the other way
around and S-R had contacted Walter about using it.

That's the info I got, I think that Selden had known LC from earlier
days in the 30s when SR was heavily into making military radio stuff
for the US Navy...didn't talk to Selden,didn't know he was still
around, my emphasis and interest was more slanted to the post-war S-R
amps and FM as AM was largely waning by then ...I have the separate
Cantilever Control basic mono amp (2 x 6L6) and tuner-preamp, I've
been looking for one of the integrated mono EL-34 amps like the one
you had, if you know of any please let me know...I have an SR-5100
El-34 stereo amp and it is excellent, along with the matching SR-2000
stereo preamp. S-R is little known, unfortunately, as they made
excallent products.


Did you interview Water Selsted about the detector?

Two permeability tuned IF 6BA6 stages
terminated into the low distortion detector (1N48 & 12AU7).

Interesting that S-R used a Germanium diode in some models, the SR-68 used
the two halves of a 6SN7, one half connected as a diode, and the other
half as a triode.

That's all the detail I have on it...it was used in the SR 51 and 68 and
808 AM/FMs and also on the SR-58 AM only, and later, in the late 50s, in
the SR1000, which had provision for mpx and modern styling. Also in
the Cantilever Control Brentwood tuner (SR100) of the mid 50s...

I had what must have been the matching "Cantilever Control" amplifier,
used a pair of EL34s in the output, and had a "scratch" filter with a
variable cutoff point controlled by a two or three gang variable capacitor
like you would find in a radio, I think it may also have had a matching
rumble filter, whose cutoff frequency was controlled by a ganged pot.

according to my notes, McIntosh was interested in the
coils specifically because of their superior specs, and attempted to
have J-R winding of LA duplicate them, unsuccessfully.

I wonder what characteristic it was about the S-R IF transformers, that
McIntosh was after?

Will mentioned 3 stages instead of 2, but I'm not sure what that
pertained to, as I am no expert on this stuff, more of a historian
than technician. It was clear that Mac was interested in the IF
performance aspect however.

They also copied the SR variable rumble filter that was designed
specifically to deal with the rumble from Garrard turntables.

Which McIntosh amplifier used the variable rumble filter, I don't remember
one, but then I am not that familiar with old McIntosh equipment?

Perhaps the C-20? I will check, I haven't gotten into the upcoming
Corderman/Painchaud/Rowley interview yet, so not up to speed on Mac
specs...

best
Roger in NY

All of this info is direct from Will Rayment, but as you said, filtered
thru 60 yrs of time, and who knows what all? Anyhow, a bit of contribution
to the history of those days.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article , donut wrote:

OK - the IF distortion was one reason that the TRF was favored for really
true hi-fidelity AM.

RF amplifiers have exactly the same distortion problem as IF amplifiers,
of course the TRF eliminates the mixer/oscillator and all their associated
problems.

How many stages of RF amplification would a TRF need to equal the
sensitivity of an AA5?

Two well designed RF stages ought to do it, the gain per stage probably
won't be quite as great as an IF amplifier stage, but this is compensated
by the fact that the conversion gain of the converter stage in the AA5 is
not that high.

I know there's a problem with selectivity but the more tuned circuits, the
better that would get.

Would 5 tank circuits and 5 RF amplifier stages, all operating near unity
gain (except for the first one) be sufficient?

5 tank circuits would be good, but I suggest using only two RF amplifier
stages, as this should be able to equal the gain of the AA5, and 5 stages
would be a nightmare to layout so you don't get unwanted feedback and
oscillation.

Just cascading 5 single tuned tank circuits is going to give you a filter
with a very poor shape factor. I suggest you use a single tuned circuit
for the antenna, and a pair of double tuned circuits, one between the two
RF amplifier stages, and the second between the second RF amplifier stage
and the detector. This will give a better shape factor. Add some series
resistance to the tank circuits, and keep the source and load resistances
high, so that the Q increases with frequency, and then on the two double
tuned circuits use the coupling scheme used by the Western Electric No.
10-A, Weeden, and J.W. Miller TRF tuners, so that the coupling coefficient
varies inversely with frequency, giving you a nice approximation of a
constant bandwidth at both the high and low ends of the AM broadcast
band. J.W. Miller called this scheme "negative mutual coupling". Don't
make the mistake those three radios did of using aperiodic coupling
between the detector, my discussion with Patrick showed why that is a bad
idea. And even more important, unless you live way out in the sticks,
don't use an aperiodic antenna coupling stage as Miller did, as this will
let the powerful nearby stations into the first RF amplifier stage,
creating all sorts of havoc.

Would each RF stage add some distortion of it's own?

Yes, the distortion situation is identical with that of the IF amplifiers.

I ask this question because I can get a 5 gang variable cap very
inexpensively.

Go for it then.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article , Patrick Turner
wrote:

To address this problem I suggest a PP IF amp isn't as crazy /wacky as you
think.
Its simply an application of the well known fact that a PP amp
using two tubes produces a far cleaner result than one SE tube,
for the amount of power produced by one tube on its own.
The dynamic range is potentially increased 6dB, or doubled, but
what I suggest is worth having is the simple absence of distortion.

I don't understand where you are getting this 6 dB figure from, I would
think it would be closer to 3 dB? Keep in mind that the distortion
reducing feature of PP amps is largely lost in this application, so the
principal advantage of the PP circuit is a doubling of the power available
for driving the detector.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

John Byrns wrote:

In article , Patrick Turner
wrote:

To address this problem I suggest a PP IF amp isn't as crazy /wacky as you
think.
Its simply an application of the well known fact that a PP amp
using two tubes produces a far cleaner result than one SE tube,
for the amount of power produced by one tube on its own.
The dynamic range is potentially increased 6dB, or doubled, but
what I suggest is worth having is the simple absence of distortion.

I don't understand where you are getting this 6 dB figure from, I would
think it would be closer to 3 dB?

Well, each half of the PP circuit can produce the same output
voltage, but oppositely phased, so potentially, there is twice the voltage
produced. Elementary, dear Watson.
The load a-a must be twice the single tube load.
But even if this isn't the case with a parafeed set up using a standard IFT,
there is still second harmonic current cancelling in the tubes, and it has to
give
lower distortion.

Keep in mind that the distortion
reducing feature of PP amps is largely lost in this application,

I am not so sure, I still think the PP would be advantageous,
and it needs to be built and measured, before deciding if its better or not.

so the
principal advantage of the PP circuit is a doubling of the power available
for driving the detector.

Well, twice the voltage output, if possible, so the detector should be made
to have as high a voltage capability as possible, able to detect 50vrms.

Then when only 2 vrms is wanted, expect thd to be negligible.

With high level signals, the snr should be excellent.
Usually, most local station AM radios are quire OK regarding snr,
its not until you get up into the high SW bands that one might think about
triode mixers, et all, for low noise, perhaps a fet input stage.

There is no other point to PP IF amps, and a CF detector, then with a CF buffer,

other than chasing fidelity.
Its easy to make a fair sounding radio with the standard fare, mixer, vari mu IF
amp,
diode detector, then two audio stages with no FB.
Fair is all it will be.

One of these days, I must try the PP IF stage, but with IF = 2.4MHz,
and two stages, the first can be a vari mu stage, since its signal is very low.
making the IFTs and oscilator coils should be quite easy; less turns,
and maybe not even need litz wire.
I recall someone even tried a higher IF frequency....

For MW, low transconductance pentodes would be best, since too much gain in
two IF stages would be a hassle.

There must be 1,001 ways of building a radio.

Patrick Turner.


Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

Patrick Turner wrote in
:

I suggest ppl who have doubt about this should go back to the old
books, and do some real study, to save us from having to regurgitate
what is in those textbooks.
So off your bums, away from the PC and start reading!!!!

1) Some of us don't have access to the old books.

2) We are helping you keep your thought processes active.

(John Byrns) wrote in message ...
In article ,
(firedome) wrote:

As for the circuit's provenance, I never said S-R invented it...it
was, as I said, an adaptation of the Selden -Smith 2 tube decector
circuit (did any one else use 2 tube detectors?) found in the RDH3.
Will Rayment never claimed to have invented it, but was the only one
to use it in a commercial product AFAIK.

I tried to email you about some information that I received from Walter
Selsted on the "two tube" detector, but your email address bounces.
Perhaps you already talked to Walter, did you interview him for your
article on the S-R tuner?

Oh, I changed ISP... it's . I wrote earlier
today Walter, I didn't know he was still with us. You might want
to talk to Will Rayment, I'm sure he'd be happy to oblige, eMail me
for contact info... An article on this AM circuit might make a good
VTV submission, Charlie would welcome a well written piece on it I'd
imagine...
Roger in NY



Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article ,
(Brian) wrote:

I pulled Sturley down off the bookshelf to check for more detail from the
reference given in the RDH4 for "Modulation Envelope Distortion". So far


When you get done reading, John, I'd be interested to know some
typical distortion figures.

OK, I quickly scanned ahead and I see mentions of things like 5%
distortion, which I believe is a typical radio design goal, so he
presumably is shooting for something like that. It looks like he
discusses how to calculate the distortion from the tube characteristic
curves, but the real meat is probably in the references he gives at the
end of the chapter, hopefully he gives enough in the book to work it out.
I see one point where he discusses calculating the second harmonic
envelope distortion by operating the tube as an audio amplifier, and
measuring the third harmonic distortion of a sine wave, this fits right in
with the discussion Patrick and I have been having.

I'll bet they're signficant only for very strong signals.

Clearly the IF amplifier distortion will go down at lower signal levels,
and of course diode detector distortion tends to rise at low signal
levels. Diode detector distortion seems rather minor until the modulation
gets high enough to get into negative peak clipping problems.

I know that some receivers attenuate the AVC to the
last IF stage to minimize envelope distortion since that's where the
highest signal levels occur.

I will have to actually read the section from Sturley to see what he is
really saying but on my quick scan, it looked like he said the distortion
actually decreases as the negative bias on the vari-mu IF amplifier tube
becomes more negative, but that is in relation to a fixed input voltage to
the grid. Clearly in a real radio if the AGC is trying to maintain a
constant voltage at the detector, then the grid drive is going to have to
increase, and my question would be how does the distortion compare then.
To ask the question another way, for a given output from the tube is the
distortion lower with high negative bias and signal input to the grid, or
with lower negative bias and signal input? It will be interesting to see
if he addresses the issue from that perspective.

Still, my guess is that this source of
distortion pales in comparison to that due to low modulation
acceptance.

But the distortion due to "low modulation acceptance" increases abruptly
at some point as the modulation level increases, while the amplitude of
the distortion caused by the IF presumably follows the second power of the
modulation level, and the third power of the signal level.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article ,
(firedome) wrote:

Oh, I changed ISP... it's .

I tried the westelcom ISP address that I had from when you emailed me late
last year, and it bounced, but the user name was "fireflite", so I assume
that was the problem. Is there an article lurking in this
firedome/fireflite business?

I wrote earlier today Walter, I didn't know he was still with us.

Yes, I assume he is, he was back in January.

You might want
to talk to Will Rayment, I'm sure he'd be happy to oblige, eMail me
for contact info...

OK, thanks, but first I want to see if I can get directly in touch with
Water Selsted, and ask him if he remembers how S-R became aware of the
detector, as that was a question I didn't think of originally, and it is
more interesting now that it appears he never published anything on the
detector.

An article on this AM circuit might make a good
VTV submission, Charlie would welcome a well written piece on it I'd
imagine...

By "AM circuit" I assume you mean the entire tuner, not just the
detector? I am most interested in the history of the detector itself, and
while I have seen it referred to as a diode detector followed by a cathode
follower, I don't feel that is an accurate description, as the cathode
follower is operating in a nonlinear mode. The Selsted Smith detector
appears to me to be a slight variation on the so called "infinite
impedance", or reflex detector, which was developed by RCA. The intended
operation of the Selsted Smith detector is somewhat obscure, I have never
seen a technical article that discusses its design and operation. I have
been trying to run down some definite information on the RCA "infinite
impedance", or reflex detector, presumably there is an RCA licensee
Laboratories Bulletin describing its design and operation, but finding a
source for the RCA licensee Bulletins from the mid 1930's is a problem.
As a result of this exchange I did stumble across a reference to a three
page 1939 Wireless World article on the "infinite impedance", or reflex
detector, in addition to the 1937 article I already have. I will have to
try and run down a copy of the 1939 Wireless World article, is anyone out
there a Wireless World collector, that might have a copy of the August 3,
1939 issue of Wireless World? Information on these old high performance
AM envelope detectors is not the easiest thing to find.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

donut wrote:

Patrick Turner wrote in
:

I suggest ppl who have doubt about this should go back to the old
books, and do some real study, to save us from having to regurgitate
what is in those textbooks.
So off your bums, away from the PC and start reading!!!!

1) Some of us don't have access to the old books.

2) We are helping you keep your thought processes active.

OK, then do some MORE research on established websites,
if you can't find the old books, which are carried by many second hand
bookstores,
some of which list their books on their websites.

I wish I had the time to restate what's in the text books all day,
but I just don't, and regurgitation would send me barmy.
And yet I don't like to see ppl continue in their ignorance,
so you'll just have to put up with a curt suggestion from time to time.
I like to try to enlighten folks about what might NOT be in the books or
so obvious.
I enjoy helping, and being there for ppl who try to help themselves,
especially if they have done some serious research they from the available
shelves full of info.

No offence meant,

And good luck with your projects, they usually take time, more time, and
tomorrow, before they amount to much.
Years later, when you see where you have been, your efforts were not in
vain..

Patrick Turner.

(John Byrns) wrote in message ...
In article ,
(firedome) wrote:

Oh, I changed ISP... it's .

I tried the westelcom ISP address that I had from when you emailed me late
last year, and it bounced, but the user name was "fireflite", so I assume
that was the problem. Is there an article lurking in this
firedome/fireflite business?

Only if you're into vintage DeSotos...another hobby...luckily,
firedome can apply equally to a certain vacuum state amplification
device...

I wrote earlier today Walter, I didn't know he was still with us.

Yes, I assume he is, he was back in January.

Jeez, he must be up there agewise...interview him while you can! This
old audio history needs to be preserved...I'm up to my ears with Mc,
Pilot, and
Stromberg-Carlson on my plate for the forseeable future, a couple
years at least.

You might want
to talk to Will Rayment, I'm sure he'd be happy to oblige, eMail me
for contact info...

OK, thanks, but first I want to see if I can get directly in touch with
Water Selsted, and ask him if he remembers how S-R became aware of the
detector, as that was a question I didn't think of originally, and it is
more interesting now that it appears he never published anything on the
detector.

An article on this AM circuit might make a good
VTV submission, Charlie would welcome a well written piece on it I'd
imagine...

By "AM circuit" I assume you mean the entire tuner, not just the
detector?

I think the detector itself and evolution of dector design in general
would make an interesting article...

I am most interested in the history of the detector itself, and
while I have seen it referred to as a diode detector followed by a cathode
follower, I don't feel that is an accurate description, as the cathode
follower is operating in a nonlinear mode. The Selsted Smith detector
appears to me to be a slight variation on the so called "infinite
impedance", or reflex detector, which was developed by RCA. The intended
operation of the Selsted Smith detector is somewhat obscure, I have never
seen a technical article that discusses its design and operation. I have
been trying to run down some definite information on the RCA "infinite
impedance", or reflex detector, presumably there is an RCA licensee
Laboratories Bulletin describing its design and operation, but finding a
source for the RCA licensee Bulletins from the mid 1930's is a problem.
As a result of this exchange I did stumble across a reference to a three
page 1939 Wireless World article on the "infinite impedance", or reflex
detector, in addition to the 1937 article I already have. I will have to
try and run down a copy of the 1939 Wireless World article, is anyone out
there a Wireless World collector, that might have a copy of the August 3,
1939 issue of Wireless World? Information on these old high performance
AM envelope detectors is not the easiest thing to find.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article , Patrick Turner
wrote:

John Byrns wrote:

In article ,
(firedome) wrote:

An article on this AM circuit might make a good
VTV submission, Charlie would welcome a well written piece on it I'd
imagine...

By "AM circuit" I assume you mean the entire tuner, not just the
detector? I am most interested in the history of the detector itself, and
while I have seen it referred to as a diode detector followed by a cathode
follower, I don't feel that is an accurate description, as the cathode
follower is operating in a nonlinear mode. The Selsted Smith detector
appears to me to be a slight variation on the so called "infinite
impedance", or reflex detector, which was developed by RCA. The intended
operation of the Selsted Smith detector is somewhat obscure, I have never
seen a technical article that discusses its design and operation. I have
been trying to run down some definite information on the RCA "infinite
impedance", or reflex detector, presumably there is an RCA licensee
Laboratories Bulletin describing its design and operation, but finding a
source for the RCA licensee Bulletins from the mid 1930's is a problem.
As a result of this exchange I did stumble across a reference to a three
page 1939 Wireless World article on the "infinite impedance", or reflex
detector, in addition to the 1937 article I already have. I will have to
try and run down a copy of the 1939 Wireless World article, is anyone out
there a Wireless World collector, that might have a copy of the August 3,
1939 issue of Wireless World? Information on these old high performance
AM envelope detectors is not the easiest thing to find.

The S&S detector has the IFT secondary grounded at one end of the coil,
and the live end connected to a tube diode in series with 250k
to ground.
So the load seen by the IF amp tube is a part only of the reflected load of a
diode
turning on through an R, and in normal operation at a few volts, the diode
conducts continuously,
because the modulation is not always much more than 60%.

If the diode "conducts continuously", why is it even in the circuit?

Thus a load of about 250k+ is on the IFT, and driving tube, and this
has a very small effect on the distortion, and far less effect than
if there was a cap to charge as is the case with most normal detectors.

The voltage at the top of the 250k is sent to a grid of a CF, and at the CF
cathode, there is a 15k to ground, with some current flow, since the carrier
input voltage means the average level is at a couple of volts.

The second tube in the "S&S detector" is not a "CF", "CF means "Cathode
Follower", and in the "S&S detector" circuit the cathode does not follow
the grid, as it does in a true cathode follower. What you are calling the
"CF" in the "S&S detector" circuit is actually noting more than our old
friend the RCA "infinite impedance", or reflex detector. The question is
how the diode added by "S&S" acts to reduce the distortion below the level
of distortion produced by the reflex detector, if indeed it does? While
the RDH4's explanation of the reasons for the distortion reduction seem
valid as far as they go, I don't believe they are the main reason for the
potential superiority of the "S&S" detector over the RCA reflex detector.
I have a couple of ideas as to what is really going on in the circuit,
unfortunately I don't have any way of proving if my ideas are correct or
not, and this isn't a matter of building and testing the circuits, because
that only shows one detector has lower distortion than the other, it
doesn't explain why.

There is a 150pF across the 15k, and this is charged positively by the 455 kHz
charge
peaks, just like a mains halfwave rectifier.
the 15k tries to discharge the cap, so the voltage at the CF cathode is like
the ripple voltage of a power rectifier, sawtooth shaped.
The AF modulation causes the AF voltage to vary at the cathode, just like a
changing
mains voltage will give a changing DC voltage at the output of a powe
rectifier.

After the cathode detection, the S&S detected signal is fed to an output to an
audio amp,
via a 0.1 uF and 1M bias resistor.

Exactly, it's not really a "CF".

That's what is shown on page 1,495 of RDH4.

BUT, some 455 kHz ripple voltage will remain in this circuit, so it should be
filtered
out further with say an extra LPF RC filter, perhaps 50k, then another 150 pF,

which would have a -3dB pole at 20 kHz, allowing a cleaner audio signal to
get to the AF amp.

The thd quoted for this detector is 0.4% at 4 Khz of AM modulation, at 80%
modulation.

And 0.33% at 420 Hz of AM modulation, at 100% modulation.

I think it can be improved easily, with the diode placed AFTER the CF, not
before,
to remove all loading effects on the IF amp, whose thd is NOT included in
the graph for detector distortion ( we can assume ), in RDH4.

It isn't at all clear why this should make a superior detector?

Then the CF can be a 12AT7, so in CF, its thd will be far less than a 12AU7.
Then the idle current operation of the CF should be with say 1.5 mA flowing
down via
a 30k RL, or more, with the IF secondary biased up at about +40v.

The diode can be a germanium type, and set up with 0.5mA of current from a
R to some -Ve voltage, and this eliminates large variations in
diode forward voltage variations, even at low signal levels,
so the diode then contributes SFA thd since it spends its life turned on all
the time.

If indeed the diode does spend "its life turned on all the time", then I
suspect that it would not make a particularly linear detector, because of
the portion of its characteristic curve that would imply it was operating
on.

Also it is my understanding that even with a biased diode of the type that
doesn't spend "its life turned on all the time", the bias must change with
signal level, or distortion the won't be minimized. This means that
either a very tight AGC circuit must be used, or the bias applied to the
diode must be made to track the signal level presented to the diode.

The value of C charged by the diode is determined by the idle current flowing
in the
diode bias resistor, and should be determined experimentally.
One of these days I'll publish my notes.

I suspect there is a bit of partisan bias in your recommendation of this
detector circuit, that is unrelated to its performance.

Expect detector to have less than 0.1% thd at any modulation F,
and up to 100% modulation.

I sure would like to have an AM generator that could produce a signal with
less than 0.1% distortion at 100% modulation, so I could measure these
effects.

I wonder what Walter might say about all this.

Probably not too much, I suspect he forgot the details of the "S&S
detector" a long time ago, after all he had much more momentous things to
think about. I am told that Walter was the inventor of the transverse
recording scheme used in the Quadraplex video recorders that
revolutionized television broadcasting back in the 1950s.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

donut wrote:

(John Byrns) wrote in news:jbyrns-1307031343160001@216-80-
74-203.d.enteract.com:

Thanks, I will check the "oldradioparts" site, I never noticed that AES
had any of the J.W. Miller IF Transformers that I am interested in.

On the AES site, hit Parts then Coils and coil forms.

The Miller NOS coils are listed near the bottom of the page. Several IF
transformers, though hard to tell if they are tube or transistor types.

I have a 1979 J.W.Miller catalog, if you need something looked up.
--


Michael A. Terrell
Central Florida