Speech Amp for Modulator

[WZ5Q]

845 PP Speech Amp for Modulator

Howdy Y'all,
My name is Mike and thanks for having me on the Forum.

I want to use Stephane Puechmorel's 845 PP Amplifier design as a Hi-Fi Speech Amplifier to drive a Modulator for an Amateur Radio AM Transmitter I am building. Here is a link to his website, the schematic of the amp and power supply.

http://www.recherche.enac.fr/~puechmor/e_projets.html

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I have some questions about this design but will give you some background on the Modulator first.

The PP 845 Hi-Fi Speech Amplifier will be driving a PP pair of 3-500Z Modulators in Class B running around 3600VDC on the plates. This will Plate Modulate a 3-1000H Low Mu Triode thru a Modulation Transformer and a Modulation Reactor. The Class B Driver Transformer I have is from a RCA Broadcast Transmitter and was designed for a pair of 845's in PP to drive a pair of 833A's in PP Class B. I am substituting the 3-500z's for the 833A's in my design.

The Class B PP Driver Transformer has the following Specifications:

20cps to 20kc Frequency Sweep = 3 degrees phase shift at 10kc, 7 degrees phase shift at 20kc
Impedance Ratio = 23:1 Pri/1/2 Sec
Turns Ratio = 4.8:1 Pri/1/2 Sec
Primary Impedance = 10KΩ Plate to Plate
Primary DCR 90Ω
Primary Inductance = 73H
Secondary Impedance = 2KΩ - 2KΩ
Secondary DCR 38Ω

The questions I have for this design are:

1- What would be the best Lundahl Transformers to use for the Input & Interstage Iron?

2 - Would there be any drastic component and circuit changes in the PP 845 circuit to use my Driver Transformer as it has a 10KΩ impedance Plate to Plate Primary?

3 - I realize that the Single Ended Tubes must use DC on the filaments due to hum, but do the PP 845 require this as well? Since there in PP the hum should cancel out, no?

Thanks,
Mike
WZ5Q
from Deep Down in the Dark Dismal Swamps of the Calcasieu

 

[Miles Prower]

Howdy Y'all,
My name is Mike and thanks for having me on the Forum.

I want to use Stephane Puechmorel's 845 PP Amplifier design as a Hi-Fi Speech Amplifier to drive a Modulator for an Amateur Radio AM Transmitter I am building.

You can stop right there. This design is unsuited for use as a plate modulator. Ham AM xmtrs are restricted to a BW= 6.0KHz, and the design shown is definitely not designed for this purpose, and Lundahl's would be wasted here. There is no bandpass limiting and the BPF you will need in front of it, and you will since there isn't enough front end gain for the proposed purpose, will waste the potential of a pricey IST.

The modulation xfmr has some impressive specs, but that was for a BCB xmtr and a 20KHz BW. You can still use that, but not at its rated BW.

Stephane's design is hideous because it was never designed for this purpose in the first place. Better go back to the drawing board, and look through older editions of The ARRL Handbook from the times before SSB really took over.

 

[Tubelab_com]

Ham AM xmtrs are restricted to a BW= 6.0KHz,

You haven't heard these guys on the air. They are more HiFi than the local AM radio stations are. They have more studio quality audio processing equipment than the usual AM radio station does too. If you have a ham radio, dial up 3620 +/- 15 KHz or so late at night. Its easy to figure out who's who.

I believe they run external audio processing before the modulator to restrict the BW. This means the modulator needs to be clean or it will generate harmonics that will be transmitted.

Look here:
WZ5Q Hi-Fi ESSB Amateur Radio Station with VooDoo Audio

As to the schematic.....I haven't tried to build anything quite this crazy, so I don't know, but I don't see why it wouldn't work. I am sure some components will need tweaking, especially the cathode bias resistors, to accommodate different tubes and supply voltages.

 

[WZ5Q]

Howdy Miles,
Thank you for your post and you opinions.
Unfortunately, you are mistaken on several accounts.

1st, there are no restrictions on bandwidth for an Amateur Radio Transmitter, AM or SSB. This is a common mistake made by allot of people. Part 97 does not give any hard rules or mandates for specific bandwidth requirements for the HF Amateur Radio service concerning A3A, J3E etc. What they do say is:

97.307(a) No amateur station shall occupy more bandwidth than necessary for the information rate and emission type being transmitted, in accordance with good amateur practice.

This has been the source of great debates as everyone reads there own views and interpretations into 97.307. That being said, I am an advocate of Hi-Fi AM and a mode called eSSB (Extended Single Sideband) which is wide bandwidth SSB.

They Key Words there are Good Amateur Practice. If the band is crowded or adjacent stations nearby, then by all means I reduce my transmitted bandwidth. To not do this is just plain rude and inconsiderate. But when there are no adjacent stations, we will increase our bandwidth and play some very pleasing and extremely nice sounding Hi-Fi AM or SSB.

I just wanted to make this point and not to drag the initial intent of this post into the slippery slope of the "Bandwidth Debate". 😀

Second, I run a complete Analog Tube Rack System for low level Audio which includes Multi-Band Compression and Limiters. I can shape my Audio into any bandwidth profile with my parametric EQ and the Multi-Band Compressors for bandpass limiting purposes. I like to do this at low level audio instead of high level as there is more control. I tend to make the higher levels less bandwidth restricted for a cleaner and more transparent transmitted Audio. Of course the Gain issue is moot using this Rack.

I like to have the bandwidth capability of my audio stages at maximum for linearity and headroom no matter what the bandwidth I will be running. This makes for a more transparent and less distorted complex waveform. This is the reasoning for wanting to use the best components available for the Speech Amp I am building for this Heavy Metal Transmitter.

The use of the BCB Driver Transformer is not only for the cleanliness of its bandwidth, but for its Class B performance of allowing the 845's to swing the Grids positive on the 3-500z Modulators. That's what it was designed for and you cannot find anything made today that will perform like it.

I have been home brewing for many years and have many of the ARRL, Bill Orr, etc handbooks which are truly a wealth of knowledge to say the least. But unfortunately they do not cover the scope of the build I am attempting now.

I have all the math done, and I have just about all the parts for this build. The only thing left is designing the Speech Amp. I like the simplicity and raw power of Stephane's design. More so because of the Driver circuit as most 845 amps have very wimpy drivers. The 845 needs about 400v peak to peak of grid drive, I like the idea of using the 211 to drive them. I also like the idea of using Iron Coupling. Another plus is the Single Ended Predriver and driver, this thing has the best of both worlds going for it. I really think it will work nicely for what I want.

All I need is some input on which Lundahl Transformers would be the best. 🙂

Take Care,
Mike
WZ5Q
from Deep Down in the Dark Dismal Swamps of the Calcasieu

 

[WZ5Q]

Howdy George!

Been a while since we have spoken, Your HY-615 Hytrons have found some nice homes!

I have my 455Kc Low Level Plate Modulated Transmitter up and running now using the HY-615 as the Plate Modulated RF Final. Man is that thing Linear! Works like a hose. I sent a few of them across the Big Pond to England to a guy thats building one from my design. He was having some issues locating some good ones so I sent a few of yours over there. 😀

Yea, I think it will work too. Of course there will be some tweaking, and I will be deviating quite a bit from his power supply design. I will be making it more dynamically regulated and adding some more filtering.

Good to hear from you again,
Mike
WZ5Q
from Deep Down in the Dark Dismal Swamps of the Calcasieu

 

[Tubelab_com]

The 845 needs about 400v peak to peak of grid drive, I like the idea of using the 211 to drive them.

Hi Mike,

I have heard you guys on the air when I was in the ham shack at work late one night. 80 meters doesn't work well at home for me since they put a 250KV transmission line right across the street from my house. The noise level is S9 or higher on a humid summer night. AT&T installed an LTE tower across the street too which killed my 902 MHz operation, so I don't even have a radio hooked up at the moment.

I know you like to use tubes where some of us would be tempted to sprinkle some sand, so go for it.

I built an 845 SE amp for HiFi use. I get the drive voltage swing by CCS loading a 45 triode and feeding it 500 volts. Then I buffer it with a mosfet source follower for drive current. You could do the same thing by choke loading a triode, and buffering it with a cathode follower. The amp makes 40 WPC in A2 with the grid going up to +60 volts.

I have this thing about not using transformers to drive tubes. You need to pay big bucks to find interstage transformers that work as well as a $3 mosfet.

Good luck on your endeavor......I would hate to see your electric bill.

 

[WZ5Q]

80 meters doesn't work well at home for me since they put a 250KV transmission line right across the street from my house. The noise level is S9 or higher on a humid summer night. AT&T installed an LTE tower across the street too which killed my 902 MHz operation, so I don't even have a radio hooked up at the moment.

Wow George,
With all the QRN, I wouldn't have a rig hooked up either. I am truly sorry to hear about that misfortune. I know they are responsible for dealing with there RFI, but its getting them to take care of it that is the problem. Being that it is in such magnitude and scope, I think I would be getting the ARRL and the FCC involved in that situation.

I know you like to use tubes where some of us would be tempted to sprinkle some sand, so go for it.
I have this thing about not using transformers to drive tubes. You need to pay big bucks to find interstage transformers that work as well as a $3 mosfet.

Yes, I do like toobage! 😀
I can and do use sand in some circumstances. I have been searching and studing the interweb for some time now trying to find a suitable 845 Speech Amp design for my project. I researched your design (nice specs and build by the way), in fact it was in my top 4 final picks, but I just couldn't bring myself to use the sand. In this instance, it needs to be all tube to fit the "motive" and "era" of this build. Lets just say it's an "Old School" build. I plan on installing 8008 & 866A Mercury Vapor Rectifiers for that nice pulsed glow from the Modulators and Drivers not to mention creatively cut viewing windows for all the tubes in the rack cabinet.

Good luck on your endeavor......I would hate to see your electric bill.

Hi Hi Hi! No Doubt. It is going to be a fun project. I have the VFO/Exciter and IPA (Intermediate Power Amplifier) already breadboarded and operational. It is a VFO/Exciter out of a T-368 Military rig which is a 160 thru 20 meter capability. The IPA is the PA Unit robbed from a TS-830 rice box. It is built around 2ea 6146 Beam Pentodes in Parallel making 150 watts of Carrier Drive for the RF Final. I use the IPA as a Doubler for 15 and 10 Meters giving me 75 watts of Carrier Drive. I vary the screen voltage for Drive Control. I am in the process of installing it in a Rack Deck at the moment.

Take Care,

 

[Mooly]

Lets keep away from politics folks. Two posts deleted.
http://www.diyaudio.com/forums/site-announcements/167561-diyaudio-rules.html

 

[mikeatoldaudiodotnet]

T-368

Mike:
Did you ever get this worked out? Looks like we're on a similar path. I'm planning on using a T-368 exciter to drive a Plasma Products HFS-1000E ( 2 X 4-400 )😱. I have a NOS RCA mod xfmr out of a 1KW rig... probably the same one you have.
I was planning on using my Norton audio amp ( 8 X 211 PPP ) but, I don't think it will swing enough to fully modulate the power amp. BTW, I'm planning on converting the 4-400's to a pair of 250TH. I may modulate with a pair 100TH or a pair of 810's. The HFS-1000 was originally on 13.56MHZ, so I'll try 14.286 first. If I can get a decent tank built I may move to 3.885 or thereabouts.

What are you using in the output of the T-368 exciter? I looked at the specs of the 6000 and a 6146 is closer than the 6AV5 or whatever else people are using.
TNX, MD, K4TQF

 

[WZ5Q]

Howdy MD,
Unfortunately, The project got put on hold as I moved the QTH and am trying to get the other house ready to sell on the market. I have been accumulating and upgrading parts in the meantime for the big build.

I settled on the Karna Amplifier as the Speech Amp to drive the pair of PP 845's which will drive the modulators in Class B. I am building the Modulator as a stand alone unit with its own variable power supply. This will give me way more then enough Audio Power and headroom to conservatively modulate just about any RF Deck with ample positive peaks regardless of impedance mismatches. I have all the Lundahl and Tribute Iron, Tubes, and parts for the Karna and modulator, just need the time to build it.
Here is a link to his website...
The Karna Amplifier

I have upgraded the Mod Iron from the 1KW BTA-1R to a 5KW model from a BTA-5R1. This should give me allot more security dealing with the high plate voltages on the modulators.

My T-3 Exciter is using the 6000. I need to tweak a little more power out of it as it just barley has enough grid swing for the Class C 6146 IPA on 20m.

Sounds like you have a nice project planned! Those 250th's are some beautiful bottles. I don't think the 100th's will have enough scrote to fully modulate the pair of 250th's at full strap, the 810's would be a much better choice.

Good luck with your project!
Have Fun,

Mike
WZ5Q
from Deep Down in the Dark Dismal Swamps of the Calcasieu

 

[Tubelab_com]

The project got put on hold as I moved the QTH and am trying to get the other house ready to sell on the market

That's how I solved the QRN issue!

After a 41 year career as a transmitter designer at Motorola, they laid me off. I recently packed up everything I could move and left the 5 million other people crowding into the mess known as south Florida behind me, and moved to the middle of nowhere West Virginia. Actually I am in the middle of a double move. We are in a temporary house in a small town while our permanent QTH is being built a few miles out of town.

The new QTH is down in a "holler" surrounded on all sides by hills ranging from 300 to 500 feet. Line of sight to anywhere is non existent so my UHF gear will be useless.

I have been out to the property with a spectrum analyzer and find a whole lot of nothing. There are a few weak AM radio stations, 4 weak FM radio stations, a weak VHF signal at 155 MHz, probably the county police/fire dispatcher, some relatively strong signals at 1.9 and 2.4 GHz which come from a neighbors microcell site and WiFi. The VHF TV station (channel 7) that is 11 miles away is visible from a few places on the property using a 3 element Yagi. The VHF station (channel 9) that is 30 miles away is visible on the analyzer in exactly one spot and too weak to be received with a TV connected to the Yagi. Verizon cell coverage is very spotty now and AT&T is non existent. Signals will get weaker when the tree cover grows back.

It will be 6 months to a year, but I will be back on the air, and after I get my Yeasu connected up and figure out what frequencies are useful, I will build a radio....but it will be mostly, or entirely solid state......That's what I designed for the last 30 years.

It's also a far shorter ride to Dayton....I plan to be there again this year.

 

[mikeatoldaudiodotnet]

WOW ! That is quite the move / change

I worked for the CN/ICRR in their comm dept for the last 3 years of my working career. I was the Motorola "radio guy". Repaired more Spectra locomotive radios and HT-1000s than I care to remember. While there, we did a big changeover from the old microwave system to fiber.
Retired in 2003 & moved to the hills of NW Arkansas Ozarks. Fortunately, I'm at 1350 + ft. But, this whole town was built largely in the 1880's & 90's & is designated a Historic District, so no towers for me. I purchased 3.5 acres of woods behind our home and built a 20 X 32 shack. I'll be string some stealthy wire antennas amongst the trees so the hysterical district snoops don't get their panties in a wad. Good luck on the new QTH !
TNX & 73, MD, K4QTF

 

[Tubelab_com]

WOW ! That is quite the move / change

My wife always wanted to move back to her home town, and after 61 years in Florida, I was ready for a change.

A tower would not do anything for me.....unless it was over 300 feet tall!

HF should be good, VHF and UHF maybe EME only, or by an indirect path. Some friends were bouncing signals off the international space station for short QSO's limited to a few hundred miles.

Back in Florida I got in trouble with the code enforcement Nazis over antennas. The short story was NO antennas at all, not even a TV antenna. Asking the mayor if he had a permit to be such an a$$ hole didn't help.

There were no antennas at all on my house for several years, but after the housing collapse in 2008, coincident with a major hurricane, the neighborhood looked like a disaster zone, and never really recovered. Code enforcement was busy chasing the squatters and druggies out, so I made a DIY TV antenna out of coat hangers....nothing bad happened.....

So I put up a wire antenna based on the W5GI Mystery Antenna. Instead of the usual matching feedline, I put a DIY tuner box at the feedpoint and used 4 wires at 90 degree angles with relays to choose any 2 wires. The Mystery Antenna is supposed to excel on 20 meters and it did. I could routinely work Europe on 14.076 using JT65 with my 5 watt FT-817. Lower frequency bands were wiped out by the power line noise.

I plan to build a bigger version of this antenna with a tuner/relay box capable of several hundred (or more) watts. There are plenty of trees and an acre to run them on.

HT-1000s than I care to remember.

I was part of the receiver design team on that radio. I spent about a year working with the Zero IF and more time characterizing the squelch circuit. I think the HT-1000 and the Jedi family were some of the best performing radios out of that factory since the HT-220.

 

[mikeatoldaudiodotnet]

Actually, all the Motorola stuff worked well. Mainly it was just keypads wearing out & mechanical stuff like that. Railroads are tough environments. I finally convinced them to buy a battery cycling machine because the guys would keep sticking them in the chargers every chance the had and wouldn't ever deep cycle the HT batteries. I built myself a "going away present" out of spare Spectra parts. I removed the transmitter. We had a 4 bay Sinclair VHF antenna that was slightly damaged, so it followed me home. Had a CDM1550 NIB, but sold it on ebay a while back. Motorola is still pretty reliable stuff IMHO.

 

[WZ5Q]

That's how I solved the QRN issue!

Now that's what I call "Taking Action" hihi!! 😀

I have always preferred country life, with room to stretch my elbows. City life just never appealed to me. I am very happy for Ya'll getting out of the "Rat Race".

Although you are down in a holler and don't have any straight line VHF/UHF communication, the EME alternative is a very good idea... although your Moon window might be very narrow.
I had my Digital EME array (2 x K1FO 17 elements) on top of a 70' tower down in the River Bottom in order to clear the tree tops for horizon to horizon coverage. It was all mounted on a modified Hazer to bring the array up and down for service and storm protection. Of course this has all been disassembled due to the move. When I set it up again, I will add 2 more antennas for a total of 4 to get enough gain to operate CW EME.

Here a few pics of that setup...

SteppIR Antenna & Company

I hope to continue with my 3-1000H AM Transmitter homebrew project in the next few months once the shop is set back up.

I have acquired a few other "goodies" that I will put on the air as well.

One is an RCA BTA-1M broadcast transmitter which has a pair of 833's modulated by a pair of 833's. This is set up for 160m AM operation at reduced power of course.

The other is a homebrew transmitter I bought from a guy up in Connecticut. It is a 4-1000A modulated by a pair of 3-500Z's. It needs a Speech Amp, so the Karna will also work for this rig as well. Another reason why I am making the 3-1000H Modulator a separate stand alone unit. I can use the PP 845 Driver output to modulate the 3-500z's in the Connecticut rig's modulator. 😀

I look forward to yakin at you on the air.

Take Care,
Mike
WZ5Q
from Deep Down in the Dark Dismal Swamps of the Calcasieu

 

[WZ5Q]

Here are some pics of my RCA BTA-1M and the Homebrew 4-1000A Transmitters...

http://www.wz5q.net/images/bta-1m/Trip home/12-BTA-1M.jpg

http://www.wz5q.net/images/bta-1m/Trip home/15-BTA-1M.jpg

http://www.wz5q.net/images/bta-1m/Trip home/4-1000rig.jpg

Take Care,
Mike
WZ5Q
from Deep Down in the Dark Dismal Swamps of the Calcasieu

 

[mikeatoldaudiodotnet]

Now that's what I call "Taking Action" hihi!! 😀


One is an RCA BTA-1M broadcast transmitter which has a pair of 833's modulated by a pair of 833's. This is set up for 160m AM operation at reduced power of course.
The other is a homebrew transmitter I bought from a guy up in Connecticut. It is a 4-1000A modulated by a pair of 3-500Z's. It needs a Speech Amp, so the Karna will also work for this rig as well. Another reason why I am making the 3-1000H Modulator a separate stand alone unit. I can use the PP 845 Driver output to modulate the 3-500z's in the Connecticut rig's modulator. 😀

Mike
WZ5Q
from Deep Down in the Dark Dismal Swamps of the Calcasieu

Mike: May I ask what the modulation transformer is in the BTA-1M ? Also, on the HB 4-1000 rig what B+ are you running on each side of the mod iron.?
Some of the guys who know better than me on the other forums are telling me I need to run the same B+ on both sides of my RCA 1KW mod iron to swing enough to modulate the finals. Maybe because this particular transformer is 1:1 ? I was reading an old 1938 article in Radio magazine about speech amps & modulators written by Douglass Fortune, W9UVC, of Thordarson. According to him you can fully modulate a Class C output with 1/4 the class B audio power, due to the nature of speech. A lot of the theories are using sine waves. He uses the peak power of normal speech as an example. In that example the "average power" generated won't exceed the tube or transformer ratings. I think his article is found here on Page 49:
http://www.americanradiohistory.com/Archive-Radio/30s/Radio-1938-04.pdf

There is a speech amp here:
http://www.americanradiohistory.com/Archive-Radio/30s/Radio-1938-03.pdf

 

[WZ5Q]

Mike: May I ask what the modulation transformer is in the BTA-1M ?

The RCA BTA-1M has it's original Mod Iron. I haven't done any testing or calculations on them yet, but the data tags state:
Modulation Transformer: PRI - 10,300/2590 ohms : SEC - 4300 ohm 1KVA
Mod Reactor: 50 Hen - .670 Amp DC - 89 Ohms Res - 5Kv INS

So it looks like the Impedance Ratio calculates to 2.39:1 Step Down and the Turns Ratio is 1.55:1 Step Down.
Plugging in the Modulation Impedance of the RF Deck 833’s and the Plate to Plate Load of the Modulator 833’s confirm the calculations.

Also, on the HB 4-1000 rig what B+ are you running on each side of the mod iron.?

I actually don't know yet, I really haven't had a chance to trace the circuitry down or test and see what the plate or bias voltage is on the modulators.
The Plate Iron is a Peter Dahl 3Kv @ 1.5A CCS unit with a bridge wrapped around it followed by a Pi Filter. Calculations look like it will provide around 3900V under full load.

This rig is using the Mod Iron out of a RCA BTA-1R, which had a pair of 4-400's modulated by a pair of 4-400's.
It's made by Electro Engineering Works with a Data Tag stating:

PRI 2560V CT .25 A
SEC 2100V .31 A
30-10,000CPS

I made the following measurements:
Dimensions - 13" high, 9" wide, and 6" deep.
Weight - 90lbs.
Type - Oil Filled.
Measured Turns Ratio is 1.25:1 Step Down.
Tertiary Turns Ratio is 100:1 Step Down.
The Impedance Ratio calculated to 1.56:1

I'm a little worried about the higher plate voltages the builder used with this Mod Iron. Commercial Iron tends to be very underrated and since it's an oil filled unit, it should be able to take a pretty good beating. I believe if I insulate the case from ground and use a secondary wiring configuration with the mod reactor which allows the mod transformer's secondary to charge up in voltage instead of grounding it, this will equalize the voltage potential in the primary and secondary windings. This should prevent any insulation breakdown allowing it to survive at the higher voltage.
As I said, I won't know till I start getting into the rig and know what’s going on with the modulator plate and bias voltages.

Some of the guys who know better than me on the other forums are telling me I need to run the same B+ on both sides of my RCA 1KW mod iron to swing enough to modulate the finals. Maybe because this particular transformer is 1:1 ?

Yes, for the most part that is true. It depends on allot of different things and everything relates to each other. You really need to determine what your actual turn ratio is on the Mod Iron. Then you can figure from there.

I generally build for expanded positive peak capability but only run my asymmetric audio at 125% Positive Modulation Peaks with 97% Negative. I like to use separate power supplies for the Modulator and RF Deck, which gives me the ability to adjust the voltage ratio (aka turns ratio).

This is a question that you need to do allot of research on. To start, here is a terrific article by Don, K4KYV who knows what he is doing. Not only does he know all the theory and math, He knows this stuff by building experience and application.

Modulation Transformer Impedance Considerations

Here is another thread with great info...

Calculating audio impedances

I was reading an old 1938 article in Radio magazine about speech amps & modulators written by Douglass Fortune, W9UVC, of Thordarson. According to him you can fully modulate a Class C output with 1/4 the class B audio power, due to the nature of speech. A lot of the theories are using sine waves. He uses the peak power of normal speech as an example. In that example the "average power" generated won't exceed the tube or transformer ratings.

This is true, but the modulator still must be capable of delivering FULL peak power for brief periods of time without distortion.
I am of the opinion that you need to build the modulator bigger then you need, at least 100%. The more audio power you have in reserve means the more headroom you have, which allows for a much cleaner signal not to mention the transient handling capability is much better.
Most will overbuild their modulators 100 to 150% for headroom and reserve. 25% is way to low in my opinion and sounds like the makings for very weak audio. With the asymmetrical male voice, you would not have enough reserve for the positive peaks and distortion will result.

Don, K4KYV sums it up by stating:
“It is better to design the modulator for output capability substantially beyond 100% modulation for two reasons: (1) to take advantage of the natural asymmetry of the human voice and achieve more sideband power by allowing the negative peaks to more closely approach 100% before flat-topping occurs on the positive peaks, and (2) to allow some unused head-room for the positive peaks, which results in less distortion and cleaner audio even when 100% positive modulation is not exceeded.“

Take Care,
Mike
WZ5Q
from Deep Down in the Dark Dismal Swamps of the Calcasieu

 

[mikeatoldaudiodotnet]

Mike:
Thanks for the info. Yes my RCA mod xfmr states 1:1 on the tag. I remember Don from the old 80M roundtables in the early '60's. He & W4OFX a ham in my neighborhood, W0OMG & Don's old friend Conn in Paducah had a regular rag chew on 80 all the time. I may have to drive over and have an eyeball QSO with him sometime before too long.

I'll be posting about my latest project on the AMNORTHAMERICA forum. It will involve this beast: EBAY item # 161486930642
It's one of those plasma generators that's on 13.56MC.😱 I have a TMC T-368 exciter and an output tank from a TMC GPT10K to convert it. I'm pulling the
4-400's out and re-building it with a pair of 250TH.
CU on the bands, 73MD, K4TQF