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 Post subject: Neutrodyne (Eagle) output circuit
PostPosted: May Tue 21, 2019 3:31 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 624
Location: Bristol TN 37620
Hi Guys,

Working on a Eagle Neutrodyne A (1923) On the 2nd audio, across the secondary are fuse
clips with a 7 meg resistor installed across the secondary terminals. Never seen a configuration
like this in any previous battery set I've worked on.

Now there's no C battery configuration. The audio feeds the grid of the last tube and returns it to A-
Would this be some attempt to enhance tone quality?


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Thu 23, 2019 4:43 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 624
Location: Bristol TN 37620
Any of our battery set experts have any ideas? Being that the clips and resistor are
similar to a replaceable grid leak cartridge, I'm pretty much guessing that its some
sort of owner installed tone control.


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Thu 23, 2019 6:23 pm 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 14352
Location: Mountains of Mourne. Ireland.
Image
Large image: https://i.ebayimg.com/images/g/58QAAOSw ... -l1600.jpg

https://www.ebay.com/sch/i.html?_from=R ... Complete=1


:) Greg.


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Thu 23, 2019 6:34 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 624
Location: Bristol TN 37620
Thanks for posting the pic Egg. That's exactly what I have. It seems that being the
resistance is replaceable, you could plug in the best sounding resistance, similar to
the replaceable grid leaks. Not exactly sure. Was looking for someone to explain
what's going on.

The resistor is not marked but measures around 7 megohms. The set plays the same
with or without the resistance in the circuit.

That pic might be my exact set (purchased from Ebay) but also don't know if its factory,
or owner installed.

regards,
Bill


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Thu 23, 2019 8:22 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 14912
Location: S. Dartmouth MA 02748-1225 USA
Unless marked otherwise, that resistance has gone way up in value. The tone won't be affected until it gets around 100k or lower. A schematic may indicate a value but it a suggestion since the resistance is easily replaceable. The resistance also provides some pulse (static crashes) protection for the windings, especially if the transformer is a higher ratio like 5 or 10:1. Try jumping with a standard resistor of a lower value and listen to the results. I do not recommend testing when there is static crashes it is still a risk of opening a transformer winding.
Save this cartridge resistor for an experimental grid leak, its value is not out of the recommended range. If you have other cartridge resistors that have gone beyond 10 megs those can be "stuffed" with the lower value resistor, a 1/10watt will slide into the glass tube...

If a horn speaker is used the lower value tone resistor will help remove some of the harshness.

FWIW The Stromberg-Carlson 500 series of 20's radios had permanent 1meg resistor across the windings.

YMMV

Chas

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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Thu 23, 2019 8:39 pm 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 14352
Location: Mountains of Mourne. Ireland.
From - Radio, May 1924

Image
Large image→ https://a4.pbase.com/o12/56/215056/1/16 ... titled.jpg

Greg.


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Fri 24, 2019 1:05 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 624
Location: Bristol TN 37620
Thanks for the info, guys. Will have to experiment a little with the
resistances I have. Only question left is was this factory or owner
installed? These sets are few and far between, and I've never
seen a configuration like it before.


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Fri 24, 2019 11:55 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1707
Location: Phoenix, Arizona
I have seen resistors across the audio grid side of the transformers on several early sets including my Radiola V.

It is my belief that the use of the clips was due to patents. The owner of the radio could snap in a grid-leak in the clip but the manufacture couldn't sell the set with the resistor soldered in without paying a license..

The Armstrong patent on the regenerative circuit does not show a grid leak resistor. In the early years the patent holders were all suing for infringement.

Obviously you need a grid leak on the detector. As the transformers used for audio had gain due ton the turns ratio, the resistor loads down the high frequency spikes.

The grid-leak was patented and the "C" battery for bias was patented.

This is my theory and may be total BS.

Jim


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Sat 25, 2019 8:39 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1707
Location: Phoenix, Arizona
Regarding your question about clips on the audio transformers.

I just checked the schematic of a Radiola V in the RCA service book and it shows 1/2 Meg Ohm grid-leak resistors in clips across the secondary of each audio transformer. The detector grid-leak is supposed to be 2 Meg Ohms

The Radiola V is about 1921 - 22 right in the middle of law suits for every widget someone had filed a patent on.

So I'm inclined to think your radio should have the clips with a resistor.

Jim


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Sun 26, 2019 1:20 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 624
Location: Bristol TN 37620
Thanks Jim,

Anything certainly was possible in the early years regarding patents and infringing.
Just odd that I haven't run into it before.


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Sun 26, 2019 2:58 pm 
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Location: S. Dartmouth MA 02748-1225 USA
The Eagle radio fan may have seen an article in a trade magazine for a "fix" of a possible problem. Decided to add the resistor or had the local radio nut add it :lol:

As good a speculation as any other reason...

YMMV

Chas

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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Sun 26, 2019 6:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 624
Location: Bristol TN 37620
Chas,

At this point all we can do is speculate. Whoever had this set originally is lost to
history but he was a radio enthusiast. This set was quite costly for 1923 ($175.00)
and is a very early serial no. The tubes are marked with labels from Waltham's
51 Courtland St. NYC (Radio Row) Its in beautiful original condition and plays great.

I played around with substituting other glass resistances in the clips (1/2 meg, 1 meg
and 2 meg) Changing the resistances definitely changes the tone quality thru a horn
speaker. 1 meg seems to sound the best, although it only works when using the
second audio stage. Whether it was an owner modification or factory, we don't know
know at this point. No other Eagle A owner has contributed.

Was it a clever run around the C battery patent, we really don't know. It does enhance
the tone. As I use an eliminator, really don't know if it saves the batteries, as the C
battery does.

The previous owner got it at an estate sale in MD of a deceased elderly Ham operator, and
didn't know anything else about it. How it got from the NYC/Newark area to MD is unknown
but the previous owners took great care of it.


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Sun 26, 2019 6:24 pm 
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Location: S. Dartmouth MA 02748-1225 USA
Quote:
and is a very early serial no.
Can't go by that either unless actual production records are known and how the numbers were sequenced.

Enjoy as you are doing :D

My current "life" hasn't allowed me to openly set up a battery radio despite owning well over a 100. Many have been on the bench for building or rebuild, operated for a couple of days then on the shelf...

Grid bias? That is a fact of tube operation. Without it the tube can draw excessive current, possibly prematurely exhausting the surface thorium in those tube types.

I am aware of the patent for the bridge rectifier, AVC and the Armstrong regenerative. I wish Alan Douglas could jump in, he was expert at the patents. For those "honest" receiver manufacturers patents were respected. For the others, especially the obscure sets as well as a lot of the "kits" patents were to be avoided as a costly expense.

If I ever get the time I would like to build a patent model of a battery set with AVC in the 20's style. FWIR the circuit is at the patent office. I am most curious how it behaves in a directly heated TRF, possibly Neutrodyne circuit...

Someone with time could amass the patents related to early radio into a reference, then publish into a book...

YMMV

Chas

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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Sun 26, 2019 7:14 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 624
Location: Bristol TN 37620
Chas,

We do know 2000 sets were made by Eagle in 1923, (based on royalties paid by Eagle to
Hazeltine according to Alan Douglass's article.) This one falls around the midpoint. However,
no factory records exist, nor do schematics. The factory in Newark was torn down years ago
for housing projects, and Eagle was bought out by Wurtilizer.

With the grid bias, the grid of the 2nd audio to returned to A- as per most of the early Neutro-
dynes, which creates adequate grid bias if you run the tubes at B+90 or lower (say B+67)
That's what brought the whole point up. Did the factory install this configuration as a tone
enhancement or an additional grid bias as a marketing ploy, or owner installation for a better
performance?

Early 1920's enthusiasts liked to experiment a lot even with proven sets like the NR5. I have
several which have a lot of owner modifications to obtain the elusive "better performance"

I'm inclined to think, at this point, it was modified by the original owner. Instead of reconfigurating
the circuitry for the C battery, he opted to add the additional resistor. Once again, no Eagle A
owner has come forward to tell what he has in his set.

You gotta fire them up Chas, especially with all the work involved in restoring a 100 battery sets.
I can only imagine the amount of work that went into them.


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Tue 28, 2019 4:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1707
Location: Phoenix, Arizona
Not to be argumentative here . . .

My personal big concern is the #60 copper wire on the transformer and speakers coils. In the case of audio transformers which usually have a step up turns ratio I can see a spike coming in from the detector and making a high voltage spike on the secondary which shorts or opens the transformer. Many old radios I have owned have been found with open transformers in locations which are dry and not conducive to corrosion.

So I had always wondered why the Radiola V has clips and resistors in the clips on the audio transformers. The official RCA service book shows the clips and the 1/2 meg resistors. So I figured they act as snubbers to keep spikes out of the audio stages. A Radiola V uses 1 Amp 01's and I don't believe audio fidelity was of interest for the set. The Radiola V is factory equipped with a "C" battery connection.

Alan Douglas points out in his material that the Grid-Leak was patented as well as use of a "C" battery bias.


Jim :)


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Tue 28, 2019 4:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 624
Location: Bristol TN 37620
Jim,

You might be right. I have no experience with the RCA products of the era. I'm more of a
Neutrodyne, "lossers" guy, although I have restored a few catacombs. My point in the post
was to find out why there's a replaceable resistor across the secondary. Was it factory or
added on by the owner? If it was added, and not factory, what is the purpose? With your
statements, why didn't other manufacturers use it if it provides help to safeguard the transformer
windings? The basic output circuit is the same from the detector onwards, whether it be superhet,
reflex, neutrodyne, or losser.

After experimenting a little, it does provide a nice tone control should you use the 2nd audio
stage. Does it help battery life? Don't know since I don't use batteries to power. From
getting all the responses here, I'm pretty sure it was added by a radio enthusiast almost
100 yrs ago to better the tone and increase battery life, the same way a C battery does, but without
changing the circuitry and adding a C battery. A quick, simple, inexpensive mod.

Back to the original question - is it a factory? Don't know. Once again, no Eagle owner here
(and I'm sure there are some) has stated whether their Eagle A set has a resistor across the
secondary of the output transformer. Until someone comes forward to say its factory or not, I
maintain its owner installed for either improved tone or battery life or both.


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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Tue 28, 2019 5:37 pm 
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Posts: 14912
Location: S. Dartmouth MA 02748-1225 USA
In the battery radio application the grid does not draw current from a source. In fact, if the grid were left open, in a very short period of time the grid becomes so negative from accumulating electrons that the potential shuts off plate current. This action can be seen in the grid leak detector. The leaks purpose is to drain away the excess and establish a grid voltage on the plate current curve for audio detection. One would say that a low value of grid leak will always work, not true. It may work but because the now higher plate current the detecting curve is shifted and sensitivity is very poor.

That said, in an amplifier the same is happening and the transformers windings are the leak resistance. Low values of shunting resistance across the windings will decrease the value of the "leak".

Returning the input circuit to either the filament + or - establishes a fixed bias in conjunction with the voltage drop from the rheostat. So the shunting resistor at high values has very little effect on the bias thus little effect on the plate current thus B battery saving is minuscule. The resistor will effect the audio wave form and will provide a shunt load for the secondary should the plate current in the primary get suddenly interrupted by the previous tube cutting off from lightning crash. It is the induced collapsing magnetic field the causes a very high voltage in the secondary like an auto spark coil.

Years ago I did forensic on several Radiola III transformers and found 3 out of 4 windings blown open with tiny copper balls in the vicinity of the break. The fourth transformer was green corrosion.

My conclusion is to state that operating a battery or any radio that uses audio transformers during a electrical event is risky, even if protection is provided.

I might also add, that mechanical failure of the filament and possibly reaching the plate or its supports could result in a substantial current surge into the transformer. In considering the home environment and users inexperienced with the delicate nature of tube radios. I would suspect that tapping of tubes to be a somewhat common but destructive practice...

I later AC sets it was common to include a cap shunting the primary of the audio output transformer. Dual purpose was to provide some tone roll off and control of the spike from electrical discharge.

YMMV

-------------- OT --------------------------

I would be interested to see an old manufacturing process of winding small gauge wire. Management of tension must be very precise and be without any inertia from the supply spool. In the textile process, thread was often rewound from a supply spool to a spool with a polished lip using or a cone universal pattern Over the supply spool was a loose "sock" of Jacquard kitting to keep the winding from sloughing off, falling and binding.

I was experimenting with braiding and used a homemade creel to support a dozen spools of 1 mil polyester mono filament, each supply spool had to be carefully positioned in a pattern. All spools were Bakelite universal wound. The end product was a braider bobbin universally wound with 12 strand, untwisted yarn for the braider carrier.

This seemed to work for textile but I don't think it is applicable to copper wire...

YMMV

Chas

_________________
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 Post subject: Re: Neutrodyne (Eagle) output circuit
PostPosted: May Tue 28, 2019 6:06 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 624
Location: Bristol TN 37620
Chas,

I understand what you're saying concerning electrical events and spikes, and the
windings could open. However I'm sure the early radio enthusiasts did use their
sets a lot and accepted open audios as part of the radio experience.


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