heising modulation

[kb3ouk]

I've been lokking at this circuit for a while now.
http://amwindow.org/tech/htm/ssmod.htm
Now my question is, could the transformer be replaced with one that has a 1:1 ratio that one side is hooked to the capacitor and ground, and the other is hooked to the plates of a pair of tubes in push pull. Is this understandable? What I saying is that in a normal plate modulated transmitter, the plates of the modulator tubes are hooked to the primary side of a modulation transformer, and the secondary is in line with the B+ feeding the RF tube. In what I am describing, the modulator tube's plates are hooked to the transformer just like in a normal plate modulated rig, but the one lead of the transformer is grounded and the other feeds the capacitor which is connected on the side of the heising reactor toward the final amplifier tube. 

[kb3ouk]

sorry for how bad this is (drew it using the mouse on my laptop and left out some parts, like the arrow to indicate that the second cap in the pi-net is varible) but this is what i am trying to describe

[flintstone mop]

What you are seeing looks like a solid state amp plate modulating a Tube Tx.
You are correct....normally the PRIMARY would bring B+ to the mod tubes. and the secondary would be as the schematic. The Choke is in series bringing DC to the TUBE TX final and the capacitor is coupling audio from the modulator to the TUBE final........No DC on the secondary of the Mod transformer. No saturation.
 
YUP just like you drew there........... YUP

[kb3ouk]

now that i think about it i believe i saw a block diagram of a 50 kw all tube broadcast transmitter once that had the modulators running into a mod transformer just like with regular plate modulation, but then that fed a heising choke, which when drawn out should look like my drawing. my question is, in the circuit that is shown on the page that i posted the link to, the transformer used has the hi-Z side hooked to the cap and ground. since the tube moduators in my drawing would also be hi-Z, then could a transformer with a 1:1 ratio be used, which would have the same impedance on both sides, right? I've seen heising circuits before that have just a single class A tube with the plate of the tube hooked directly to the side of the reactor toward the final.

[KE6DF]

"I've seen heising circuits before that have just a single class A tube with the plate of the tube hooked directly to the side of the reactor toward the final."

That's the original, 1930's version of heising modulation. It's  not very efficient and limited in power because the mod tube runs in class A.

The modified heising circuit with the transformer you posted first lets you use two tubes in push pull class B for greater efficiency and power.

[KA2DZT]

You can also connect the capacitor from the B+ terminal (the terminal you have grounded) to ground and then connect the RF terminal directly to the mod reactor.

Fred

[K1DEU]

Here are some of my pages on Modified Heising

http://www.hamelectronics.com/k1deu/pages/ham/transmitters/am/pages/using_audio_reactor.htm

Web Site  http://hamelectronics.com/

[flintstone mop]

Here are some of my pages on Modified Heising

http://www.hamelectronics.com/k1deu/pages/ham/transmitters/am/pages/using_audio_reactor.htm

Web Site  http://hamelectronics.com/

Proven circuits that always work.

[kb3ouk]

So the only diffference between A and B is A has dc on the secondary and B is grounded. basically, it is similar to my schematic, except for the resistor and the second cap. Which if I am reading this right, are there to increase the lows that the circuit can pass?

[K1DEU]

So the only diffference between A and B is A has dc on the secondary and B is grounded. basically, it is similar to my schematic, except for the resistor and the second cap. Which if I am reading this right, are there to increase the lows that the circuit can pass?

There is no difference in Frequency response Passed for either drawing.

[K1DEU]

So the only diffference between A and B is A has dc on the secondary and B is grounded. basically, it is similar to my schematic, except for the resistor and the second cap. Which if I am reading this right, are there to increase the lows that the circuit can pass?

There is no difference in Frequency response Passed for either drawing.

Make sure the output filter cap (C2 in my drawing) for your HV supply has enough C for good lows.

Depending on the modulation transformer ratio I usually run 1 1/2 times more HV on the modulator tubes than the quiescent RF amplifier Plate modulated B+ supply.   Yuck more parts, but

To understand a circuit better draw the complete circuit without ground symbols anywhere. John, K1DEU

[KE6DF]

Make sure the output filter cap (C2 in my drawing) for your HV supply has enough C for good lows.

John, K1DEU

John,

How much would you recommend? Is something like 40 mfd enough?

Dave

Well I answered my own question by reading your document -- with my eyes open this time.

20 - 30 mfd

[k4kyv]

sorry for how bad this is (drew it using the mouse on my laptop and left out some parts, like the arrow to indicate that the second cap in the pi-net is varible) but this is what i am trying to describe

The problem with that circuit is that the secondary of the mod xfmr is hard-wired to ground, putting full DC plate voltage to the modulator between the primary and secondary windings at all times.  An invitation to transformer failure.  Better to put the coupling cap between the bottom end of the xfmr winding and ground and wire the top side directly to the PA. That way, the only DC voltage that appears between windings is the difference in plate voltage between the modulator and final.  With a common power supply, the difference is zero.  There may be transient voltage differences, however, with peaks as high as the DC plate voltage to the modulator, but at  least the transient peaks have less opportunity to do damage than would 100% duty cycle.

The safest way to do this is to return the coupling cap to the +HV from the PA power supply, but by doing this, the audio return is through the PA power supply to ground.  This can introduce hum and in some cases, harmonic distortion to the audio, and since the coupling cap and power supply filter cap are in series to ground, it effectively reduces the value of the coupling cap. Most BC transmitters return the coupling cap from the bottom end of the winding to ground, which is probably the best compromise.

[kb3ouk]

I meant to increase the response when comparing it to what i drew out, not from schematics a and b. second, i know that the schematic i drew isnt right, its not like i was going to use it anyway, i justed wanted to provide an example of what i was trying to describe, all i did to make that schematic was take the one off of the am window site and make it look like the primary was hooked to the plates of the modulator tubes, instead of to an audio amp like in the schematic off of am window.

[K4TQF]

Have any of you ever heard of this guy?

http://www.radioworld.com/article/loy-barton-a-forgotten-radio-pioneer/18284

[W4RFM]

This is an excellent read, thanks for posting.

[KA2DZT]

Read the whole story, very interesting,  everyone on hear should read it.

Fred

[DMOD]

Have any of you ever heard of this guy?

http://www.radioworld.com/article/loy-barton-a-forgotten-radio-pioneer/18284

Yes, LeRoy Barton wrote many articles on Modulation:

Phil - AC0OB

[w5omr]

sorry for how bad this is (drew it using the mouse on my laptop and left out some parts, like the arrow to indicate that the second cap in the pi-net is varible) but this is what i am trying to describe

The problem with that circuit is that the secondary of the mod xfmr is hard-wired to ground, putting full DC plate voltage to the modulator between the primary and secondary windings at all times.  An invitation to transformer failure.  Better to put the coupling cap between the bottom end of the xfmr winding and ground and wire the top side directly to the PA. That way, the only DC voltage that appears between windings is the difference in plate voltage between the modulator and final. 

One side of the mod xfmr to ground, is the original way I had connected the 250THx250TH rig, and had a pair of 4uF @ 4kVDC capacitors in parallel to couple the audio from the final-side of the mod xfmr. 
After reading discussions between you and others on the subject, Don, I removed one of the 4uF caps, and placed it, between the low-side of the mod xfmr and ground.  I couldn't tell a bit of difference in the audio.

73 = Best Regards,
-Geoff/W5OMR

[Steve - K4HX]

More from Loy Barton here.

http://www.amwindow.org/tech/htm/barton/1.htm

[KB5MD]

Interesting article on Loy Barton.  It's nice to know that a fellow Arkansan is responsible for an invention that we AMers use extensively.

[K4TQF]

Phil Said "Yes, LeRoy Barton wrote many articles on Modulation:

Phil - AC0OB

Phil, & others. Loy Edgar Barton first put forth the idea of "class B high level plate modulation" in his 1925 Master's thesis at the University of Arkansas, Fayetteville. He went to work for GE for a couple of years, then returned to U of A and secured funding for the  worlds first plate modulation transformer. He wrote the specs and in 1928 installed it in the school AM transmitter, which he also designed & built. His paper "A Plate Modulation Tansformer for Broadcasting Stations" was published  in the U of A bulletin in 1930. By then the plate transformer had been in use for 2 years. He then left Arkansas to work for RCA. They had recognized the importance of what he had done and were gearing up for the 500KW WLW fire breathing monster. Barton applied for and received US patent # 2,063,290 RADIO SIGNALING SYSTEM, Original Filed Jan. l5, 1932 - INVENTOR Loy E. Barton.
This type of modulation was used in virtually all AM broadcast and many amateur transmitters thereafter until displaced by digital modes in the 1990's-2000's. It is NOT modified Heising.

 R.A. Heising himself had this to say about Loy Edgar Barton's work in October of 1931:" The discussor feels this paper (ibid., vol 19, pp 1131-1150, July, 1931) commends itself to a large part of the radio engineering field. It is of special importance to engineers concerned with the development of transmitters. The paper should be read by everyone who contemplates developing apparatus in which power efficiency of the radio equipment is important. Push-pull amplifiers have been used in communication circuits for many years. They have usually been employed for reduction in distortion, or for providing a balanced circuit arrangement. Barton's paper emphasizes a long neglected use which results in increased output power, and decreased dissipated power simultaneously. This is accomplished by using a separate tube to amplify each half of the audio wave. This circuit instantly commends itself to those interested in audio-frequency power at high power levels. The operation of loud speakers will probably occur to us as its widest field of application, but a very important field also exists in connection with radio transmitters. It is the latter application that is discussed further, ie that in transmitters employing plate circuit modulation of the power tubes, the over-all power efficiency is brought to a relatively low value by the power consumed in the modulators. By embodying push-pull modulator tubes, with a bias which is very close to the cut-off point, the power consumed in the modulators is almost eliminated during quiescent periods, while during talking periods the efficiency of the modulators is more than doubled. The improvement in efficiency in the modulators, therefore, has the very important effect of raising the plate circuit efficiency of the transmitter to a value double that of the next best system." Published in: Proceedings of the Institute of Radio Engineers (Volume:19 ,  Issue: 10 )

[K4TQF]

Gerald Stanley of Crown Had this to say about Loy Barton in his 1996 white paper.

Reinventing the Power Amplifier - BCA

THE BALANCED CURRENT AMPLIFIER - A NEW PARADIGM FOR THE 21ST CENTURY

In 1931 Loy Barton, a research worker employed by David Sarnoff , unearthed the paradigm that has dominated all electronic power amplifiers used for audio reproduction and industrial power to this present day. Many incremental additions have embellished Loy’s original invention since its inception. The embellishments have many names, ultra-linear, Williamson, full complementary, quasi-complementary, quasi-linear, class-G, class- H, grounded-bridge, class-D, etc. One common thread in all of the above is the use of push-pull circuitry. Loy did not invent push-pull circuitry. Class-A push-pull amplifiers were around before 1931 and were used whenever larger output powers were needed than could be derived from a single device vacuum tube output stage. Loy was the first to describe class-B push-pull amplifiers which he developed to power both the large audio modulators of AM broadcast stations and the output stages of home radios. Both applications had a common need, the need to produce more high-quality power output with less electricity and natural resources.

In 1931 Loy Barton published “High Audio Output from Relatively Small Tubes” in the Institute of Radio Engineers proceedings. The very theme of the article is in harmony with the goals of every designer who has ever wrestled with the power amplifier problem of wanting unlimited output power from a small box of affordable cost. There are some things which do not change. One thing has changed since 1931 and that is the variety of electronic devices which are available to implement circuits. The original electronic power devices were vacuum tubes which were characterized by large output impedance’s and high saturation resistance’s. They made poor power switches and were most useful when used with transformers to match their output impedance to lower impedance loads such as loudspeakers. Today’s solid-state devices such as power MOSFETs offer characteristics which are most appropriate to make high speed switches, not linear output stages as practiced by Loy. Loy’s genius was to operate the two tubes of his class-B output stage in strict time alternation. To produce one polarity of output current he would turn on one tube; to produce the other polarity of output current he would
turn on the other tube. Previously with class-A designs, both tubes were always turned on and even at no signal were dissipating large amounts of quiescent power. By careful selection of the class-B bias point, he was able to produce essentially undistorted output without having a massive quiescent power loss. This greatly increased the power output that could be obtained from a pair of tubes and reduced the wastage of electricity. While many variations on this basic theme have been developed since 1931, Loy’s class-B paradigm has survived unchallenged. Operation of the push-pull power devices in time alternation has been part of all high performance designs for the last 66 years. Even when the devices became class-D PWM (Pulse Width Modulation) switches, they were operated using the class-B paradigm, first one on and then the other, in strict time alternation. While switching and PWM methods are the methods of choice to all modern power electronics engineers, PWM amplifiers have remained relatively useless for precision power amplification. Ironically the class-B paradigm lies at the heart of the problem. To produce a class-D PWM amplifier with low amounts of distortion near zero output current, it has been necessary
to operate the time alternating power switches with very precise sequencing of the two switches. If the switches have any dead time (no switch on) between their activation large amounts of distortion will form. If they overlap, the circuitry would self-destruct with large amounts of shoot-through current. The circuitry has been designed around the paradigm and is therefore not tolerant of any violation of time alternation. So pervasive has been the paradigm that it has gone unchallenged until now. While Loy’s class-B paradigm has served us all well for most of a century, its days are numbered. With a marked bifurcation in design concept, the paradigm for the next century uses simultaneous activation of its push-pull switches and has been appropriately dubbed a “Balanced Current Amplifier”.

[N1BCG]

"I've seen heising circuits before that have just a single class A tube with the plate of the tube hooked directly to the side of the reactor toward the final."

That's the original, 1930's version of heising modulation. It's  not very efficient and limited in power because the mod tube runs in class A.

The modified heising circuit with the transformer you posted first lets you use two tubes in push pull class B for greater efficiency and power.

KE6DF made a good point that shouldn't be glossed over. A Heising modulation scheme has neither a transformer nor a D.C. blocking cap. For accuracy, the word "Heising" doesn't really apply to this thread.  B'cast transmitters have long employed chokes and blocking caps to reduce saturation on mod xformers but that design is neither Heising nor "modified Heising". Just trying to clarify a common misunderstanding.

[K4TQF]

[/quote]
KE6DF made a good point that shouldn't be glossed over. A Heising modulation scheme has neither a transformer nor a D.C. blocking cap. For accuracy, the word "Heising" doesn't really apply to this thread.  B'cast transmitters have long employed chokes and blocking caps to reduce saturation on mod xformers but that design is neither Heising nor "modified Heising". Just trying to clarify a common misunderstanding.
[/quote]

THANK YOU, for the clarification.