K7DYY "Super Senior" AM Transmitter
Original 160/80 Model -and- New 80/40 Model NOW SHIPPING
  

Note: if you are looking for the K7DYY home page, here it is: www.k7dyy.com.

I have had this Super Senior AM transmitter for 80/160 since 2013 and the 80/40 version since 2015, and it has delivered everything I expected from it and more. The audio reports are all enthusiastic whether I am using the D104 mike processor that goes in the base of the microphone or the audio chain. I would recommend it for anyone that wants a high quality AM signal at full legal limit. The front and rear panel connections for both rigs are identical. The drive level for them is different though, so be careful when cable swapping to reset the audio level. The 40 meter rig exhibits an upward drift in carrier power level. Mine drifted from 375 watts output carrier cold to 420 watts hot. I adjusted the cold output to 300 watts and it stayed within its limits (375 carrier out) just fine, for a safety factor. I also run the 160/80 at 300 watts. I experience NO safety trips when running this way into a coax fed dipole.

News Flash August 2017: QST Reviews the K7DYY Super Senior AM Transmitter in September 2017 issue.

This positive review of the K7DYY Super Senior AM Transmitter should authoritatively answer any remaining questions about the technical performance of this equipment. Lab tests show that the K7DYY Super Senior met all FCC specifications. It also reports the results of the use of this rig in the AM Rally at W1AW. In fact, if you want to hear a K7DYY rig on the air, listen to the AM bulletin from W1AW on 7.290 MHz at 0145Z or 9:45 PM Eastern Time. There is a link in the QST review of the K7DYY Super Senior on youtube, as well as a link to ARRL multimedia for a recording of the audio of the K7DYY Super Senior. The author notes that using window line feeders to an 80 meter doublet antenna during rainy conditions, you can get SWR safety shutdowns. He did not state the transmatch used during the tests. Reducing carrier to 250 watts output avoided shut down under these conditions. Under normal conditions, the reviewer, W1ZR, found that setting the carrier to 325 watts output and limiting the modulation peaks properly caused no safety trips. He notes as I do that the carrier output drifts upward slightly during operation, and the level should be set a few minutes into a transmission for best results. After initial setting, it is stable. There are variations between 80 and 40 meter output that my require readjustment when changing bands. ARRL used the following audio chain for a first rate station setup:

  • Shure SCM268 five channel mixer ($315)
  • BBE EQA231 dual channel 31 band, 1/3 octave graphic equalizer ($145)
  • Behringer Pro-XL MDX2600 Composer compressor/limiter ($130)
  • Orban Optimod 9300 AM Audio Processor ($4,950)
  • Radio Engineering Associates AMM-SD1 Series AMplitude Modulation Monitor ($210)

Click on the photos above to see more detail, for settings of my audio gear, which uses the same MDX2600 and a cheaper Radio Shack 10 band EQ. Be sure you use a peak limiter in the audio chain to prevent over 100% downward modulation. Otherwise, you will get repeated protection trips. I use the right hand channel of the MDX2600 for the peak limiting function only; it is not a $4,950 Orban Optimod, but it works well enough. Don just bought me a new toy, the BBE EQA231, which will allow me more exact adjustments to transmitter frequency response, and to cut excessive high frequency bandwidth without losing lows (as happens when I use the Heathkit filter shown in the photo). I am possibly looking at the Innovonics 223 for a modulation limiter for UNDER $1000 instead of the $5000 Orban Optimod. This is a NEW redesign of the popular Innovonics 222, which is no longer in production. For the prices on the used 222s out there, you might as well buy a new 223, with improved specs. The look ahead limiter system will not allow overmodulation peaks to slip through. Also, you can select the high frequency limit of the sharp output filter easier than on the 222, for work near the high end of 40 meters. Are you listening, Santa???? Here are its impressive specifications:
http://www.inovonicsbroadcast.com/product/223.

DO NOT USE A SYMETRIX 528E WITH A K7DYY SUPER SENIOR, UNLESS YOU FOLLOW IT WITH A PEAK LIMITER. An example of a popular compressor that does NOT have a peak limiter, the Symetrix 528E has compression and parametric equalization, but does NOT have a "hard limiter" to prevent the audio drive from exceeding 100% downward modulation (on the scope it hits the base line at 0%). I get inquiries on this from time to time. If you have a 528E, you MUST follow it with a peak limiter, and it will be OK. The Behringer Ultra Voice Digital VX2496 is also a nice processor but it has NO peak limiter. You would be better off to get the Behringer Pro-XL MDX2600 and use an external multiband EQ. If you use either the 528E or the VX2496, you MUST use an external limiter, such as the Innovonics 223. Otherwise, you will be one of the people complaining about protection trips. If you exceed 100% modulation, the K7DYY trips on protection; its doing its job correctly.

I used a Behinger Ultra Pro MDX2600 two channel processor and a garage sale Radio Shack Equalizer; the left channel of the Behringer is for the mike compression. I replaced that EQ with the one W1AW uses, the BBE EQA231 dual channel 31 band. The left channel of the MDX2600 feeds the EQ. The two stereo halves of the EQ are cascaded, allowing a little more 8 KHz cut on the right channel, but otherwise flat. I removed the older Heathkit brick wall elliptic function filter is no longer needed, since the BBE EQA231 dual channel 31 band EQ has nice low and high cut filters of 12 dB per octave. Then the audio comes back to the right channel of the Behringer MDX2600, which is set ONLY for peak limiting (clipping) and a very light amount of De-Essing (the light almost NEVER comes on). This prevents overmodulation or excess high frequency energy from ever reaching the K7DYY Super Senior transmitter. All the filters and EQ are set for unity gain; this allows you to quickly switch any one of the elements OUT, for a quick comparison, without any knob twisting to compensate for level changes. If you are running a lot of presence rise above 4 KHz, this will protect the Super Senior from excessive fast transients of over modulation in the negative direction. This is especially important in the 40 meter model, which has a very agressive protection circuit, which was necessary as a fix to prevent the failures observed in the Beta test model that I had. I sent my Beta test 40 meter unit back to Bruce with some observations that resulted in changes to the production models that eliminated that failure mode. The adaptive tuning step feature, and the muting of transmit audio in "tune" mode, also was added at that time. If you are getting protection trips on modulation peaks (assuming you do not have tuner arcs), back off the presence rise so it is not so "hot" at the top end and try it again. Some limiter circuits are not fast enough to catch the overmodulation on very fast high frequency peaks. If you spend the extra bucks on the Innovonics 223, you will not have to worry about this.

Also, use the Mark 2 D104 audio processor board with the 40 meter Super Senior. The first versions did not have the proper protection for the 40 meter Super Senior; that is why there is a Mark 2 version. If you had an older 160 Super Senior with the older D104 processor board, that may be why you are getting protection trips using the same D104 processor on your new 40 meter Super Senior. The earlier D104 processor boards still work fine on the 160/80 Super Senior and your vintage equipment.

Be sure there is no arcing at the antenna tuner or on the open wire line, if you are using that equipment. I prefer to use high quality coax feed; the losses at these frequencies are so low, there is not enough advantage to open wire to justify its quirkiness. If you are using Alpha Delta antenna switches, the lightning protector arc plug will fire if the SWR at the point of the switch exceeds 2:1. The newer switches have a label on the bottom that states that. If you have this problem, simply unscrew the brass screw that holds the arc plug and remove it; put it in a plastic bag stapled to the manual and put it in your manual drawer. Screw the brass arc plug access screw back in just flush with the surface of the Alpha Delta switch enclosure. Be sure you adjust the antenna tuner to exactly 1:1 SWR using an MFJ-212 noise bridge. Or you can homebrew a noise bridge from a Ten Tec 1051 board as described at Ten Tec 1051 noise bridge

This is a full legal limit, all solid state AM transmitter producing 1500 Watts PEP. Think about it. If your 4-400 AM rig had repeated Screen Current protection trips, you would check it out before continuing to operate it. Just because this rig does not have spectacular arcs inside the cabinet, do not ignore an improper operating environment. The protection circuits are doing their job. Investigate.

If you observe these precautions, operating this radio will be a pleasure to both you and the listener. You may not be able to get a perfect 1.00:1 match with a Johnson KW matchbox. Having only two knobs, it has only that many variables to change the equation to obtain a match. That is why I built my own transmatch, which is a Murch style design with 3 adjustments..

The rig comes with an operating instruction sheet that is one page. Probably that is all you really need once you get it set up. After all, the front panel has only a power switch, a VFO knob, and two toggle switches. There is a status panel (Frequency, HIGH SWR, Transmit indicator) and an audio input jack. The rest of the panel is covered with fans. I am elaborating a bit here to share my experience with others to shorten the learning curve if you have never encountered one of these before or you are a newcomer to AM. Or maybe you are reading this as you consider whether you want to acquire one for yourself. The manual also includes a complete parts list and other information which will be useful during installation. You can download a manual from the K7DYY website referenced at the end of this article.

Low impedance drive at roughly "line level" is required from the audio source. There is a lot of switching energy in the small box that can get into the signal. The D104 processor provides the 6.8 Meg load to the D104 crystal element for good low frequency response. It provides a compressor that makes a lot of punch to the signal without being obtrusive about it. It also has a low impedance output with a level control that is set and forget once you have adjusted it with your scope. If you have both the 160 and 40 meter K7DYY Super Senior transmitters, you will need to compensate for different audio drive levels. See my article on scopes for the right waveforms. The RF envelope waveform is the only one that you can implement for monitoring on the K7DYY AM rigs. I doubt you could display a trapezoid pattern without digging inside the rig. Alternatively, you can use a more complex audio chain to drive it and play with equalization and other finesses. But to just get it on the air, the D104 board is great. See the separate photos and article on that. Yes, you can also use the D104 board with a small electret condenser mike element as well. One possibly negative comment: some people have commented on the noise gate that is integral to the IC used in the earlier versions of this processor. I tried to defeat it using a technique I found on the web and was unable to get performance that satisified me; I have written a separate article for that project. I personally do not find the noise gate that obtrusive, but I have now moved the earlier boards over to my vintage SSB equipment, where the noise gate is not a problem. I use the newer D104 audio processor boards with my vintage AM equipment also.

Observe RF safety rules for antenna location. This is a full legal limit rig.

Provide a low SWR to the K7DYY rig. I use a tuner with a coax fed dipole antenna. The only load this rig sees direct is the Bird 1 KW dummy load. The homebrew tuner is shown in a separate article. I recommend the larger Palstar tuners if you want a commercial one. The big MFJ-9982 for open wire or the MFJ-989D for coax feed might also do it. If the antenna SWR is less than 4:1, the Dentron 2000 might do the job. The Ten Tec 238C is not a "high power" tuner and probably will not cut it on 160 and possibly 75 meters, due to the small disc ceramic capacitors failure and drift in value from heating (see my repair article on the 238B).

The K7DYY AM transmitter provides a 60 to 70 Watt low level (about 20 watts on the 40 meter model) signal for adjustment purposes. My power meter had some crazy readings due to waveforms resulting from high SWR when the tuner was way off resonance. I found a better way and it protects the K7DYY from bad load conditions. The only time I ever use this low power feature is to do a tuning check on the power meter, right before going to high power.

I use an MFJ212 noise bridge or a clone I built based on a Ten Tec kit board. (See my review and construction article on noise bridges.) These are not your average noise bridge. The old Palomar Engineers noise bridge of another decade had a constant noise output that was hard to distinguish from band noise. Both of the newer styles I mentioned pulse the noise so that it is easily distinguished from the band noise. It makes a choo-choo train sound. Insert the MFJ212 or the clone between the receiver and the antenna T/R switch. That way no expensive high power switching is necessary to protect the noise bridge. Once I have the antenna matched, I test the match with the 60 watt low level signal from the K7DYY observing the wattmeter. If it shows a good match, I go to high power. This also greatly reduces QRM from tuning up on a QSO. NOTE: Do NOT modulate the low power signal used for tune up. He warns you about this. Not sure what happens if you do this. The production run 40 meter models incorporate a mute function to prevent modulation in tune mode.

If you are using open wire line to a Johnson KW matchbox, I strongly advise you obtain an MFJ212 or build a Ten Tec 1051 noise bridge kit to avoid possible damage to any of your rigs. NOTE: The smaller Johnson matchbox is not big enough to use with this rig. The KW matchbox is rated for 4 KW peaks. If you run open wire, you have become used to the drifting SWR from rain or ice on the feedline. Your 4-400 screen current protection relay may trip, but the tube will forgive you probably, if you have no zorches. This is a solid state rig (with no output tuning circuit) which depends on a nearly perfect SWR on its output. If you get any protection circuit trips, take it as a warning to correct the problem; do not subject the rig to repetitive abuse. I abandoned open wire feeders in favor of multiple coax fed resonant dipoles. In my estimation, the only good reason for using open wire line is that you can only put up one antenna, and you want to operate it on every band from 160 to 10 meters. The consequence is that the transmatch needs to be built with much wider spaced capacitors and much heavier wire in the inductors than you would use for a comparable tuner for coax feedline. I do not recommend any sort of balun on an AM transmitter of this power level, unless it is a simple "choke" balun with beads over the coax. Check for heating, if you try one. Furthermore, a transmatch that operates well on 160 will not work efficiently on 15 or 10 meters, negating any possible gain you might think you have in some random direction from the malaria germ antenna pattern on those bands. You would be better off with an elevated ground plane or separate dipole system for 15 meters and up. My dipole was rubbing against a tree at one point, and the Valiant plate current jumped from 300 mA to 340 mA and the reflected power meter was showing intermittent visible levels. I did not let this problem persist. I got out there with a long handled tree saw and amputated the offending limb. Before I trimmed the tree, I did not use the K7DYY rig as a precaution. While we are on the subject of antennas, do not use inferior center insulators or cheap plastic end insulators. The PVC spreaders I use in my broadband antenna are very long, are not at the end sections (where higher voltages live), and have end caps and drain holes in the bottom to deal with moisture.

The transmitter comes set for full 375 wattts carrier; theoretically the modulation takes this to 4 times that or 1500 watts on peaks. Most voices do not cause theoretically ideal lab waveforms. I reduced the power to 300 watts carrier when cold, to allow for non symmetrical voice characteristics and a slight upward carrier level drift, just to provide some headroom. Some people run them at 250 watts carrier, if they are getting modulation safety overload trips due to inadequate peak limiting in their audio chain. The K7DYY AM transmitters WILL make full peak legal power under normal operating conditions. PEAK power MUST be limited at 1500 watts or you will get a protection trip. NEVER exceed 375 watts carrier, warm or cold. NEVER overmodulate in the negative direction so that the scope shows the envelope going to zero (hits the baseline) or you will get protection trips. You MUST use at least a negative peak limiter in the audio chain. If you operate properly, you will not get protection trips, unless there is a flaw in the antenna system.

If you use an external audio chain limit the high frequency in the output. The K7DYY AM transmitters go 20 Hz to 10 KHz at the 3 dB points on the 160/80 rig. The 40 meter rig is -3 dB at 8 KHz. A low pass filter is advised somewhere in the audio chain. This is especially true for 40 meters, where the band edge is adjacent to the AM window. If you operate on 7295 and have an 8 KHz audio bandwidth, your upper frequency sideband edge is at 7303. The response drops off smoothly from the -3 dB point and can still stretch out quite a way. I use a brickwall filter set to 3.5 KHz max audio bandwidth when near the band edge. Most legacy receivers are 6 to 8 KHz wide and will not benefit from more than that anyway. A software defined radio can be set to 20 KHz wide or more and the brickwall filter and Equalizer on the transmitter turned off, and music sounds great played through the K7DYY rigs. (Please do not do this into an antenna! Use a dummy load for this test!)

Nominal power drain is only 5 Amps at unmodulated carrier, slightly more on peaks. I have a separate 10 Amp fused filtered AC supply. I will provide an exact measurement at a later time with full modulation. I have a 230 VAC 30 Amp line to the shack, for my SSB linears, but that is not needed for the K7DYY Super Senior.

The K7DYY AM transmitter is easy to interface with a classic receiver. But I plan to use a solid state receiver in the future. I included a second relay to short the receiver antenna to ground during transmit for better isolation. I also provided a lamp fuse and a pair of signal diodes to protect the receiver front end as is commonly found in communication monitors of a bygone era. Probably not necessary for tube radios. But it did make headphone monitoring while transmitting a snap by reducing the signal enough so that there is no distortion. I was nervous putting tube receiver plate voltages on the muting contacts of the K7DYY AM transmitter. This also is included in my external relay box. It may be over thinking the design, but better safe than sorry. It also saves wear and tear on the relay inside the K7DYY switching receiver B+. I will provide a schematic of the T/R external box later.

All connectors required for installation of the K7DYY AM transmitter are included with the transmitter as shipped from Bruce. The receiver antenna output is a BNC. The original DIN connector on the oldest 160/80 models for T/R switching and other control connections is updated with an 8 pin mike connector you can get from Radio Shack. The front panel 4 pin audio jack is also a common Radio Shack part, if you want to provide for more than one mike or an audio chain. NOTE: VERY IMPORTANT! NEVER PLUG OR UNPLUG CONNECTORS WITH THE POWER ON!!! If you do not align the connector properly and make the wrong connection it is possible to damage things. This is just common sense, but even experienced operators can get rushed.

Fan noise is minimal. I have installed the K7DYY AM transmitter high up in a rack away from the mike. One of the photos circulating on the net and on the front cover of Electric Radio shows the mike right in front of the fans. Also, I have adjusted the compression of my K7DYY D104 boards to reduce fan noise by changing one resistor value from 100 K with a 22K parallel resistor; see the article on this page.

The K7DYY AM rig runs stone cold when connected to a proper low SWR load. Old buzzard transmissions of 10 minutes leave the whole case and exit air cool to the touch. He has done a great job of ensuring excellent device protection from heat. Keep SWR very low. Class D rigs do not like high SWR and you will get the rig hot if you are careless about this operating necessity.

I provided for a large red transmit LED and an old buzzardly VU meter with a level control (to compensate for the difference in input audio levels for the 160 and 40 meter rigs) on a separate panel. This kept all the wiring tidy between the audio chain and provided an obvious ON THE AIR indicator. I will provide a schematic for the hookup if you want to do this. I also need to provide a switch to change between the 160 and 40 meter versions of the K7DYY so that I can share the audio chain and receiver. I run the audio EQ in cascade for extra attenuation above 4 KHz.

FREQUENTLY ASKED QUESTIONS:

Bruce, K7DYY answers questions about the "Super Senior" AM transmitters: http://www.k7dyy.com/p/f-q.html

Here are some other questions I have been asked about the K7DYY rigs:

I GET A LOT OF PROTECTION TRIPS ON VOICE PEAKS. I AM USING A SYMETRIX 528E IN THE AUDIO CHAIN.

DO NOT USE A SYMETRIX 528E UNLESS YOU FOLLOW IT WITH A PEAK LIMITER. An example of a popular compressor that does NOT have a peak limiter, the Symetrix 528E has compression and parametric equalization, but does NOT have a "hard limiter" to prevent the audio drive from exceeding 100% downward modulation (on the scope it hits the base line at 0%). I get inquiries on this from time to time. If you have a 528E, you MUST follow it with a peak limiter, and it will be OK. The Behringer Ultra Voice Digital VX2496 is also a nice processor but it has NO peak limiter. You would be better off to get the Behringer Pro-XL MDX2600 and use an external multiband EQ. If you use either the 528E or the VX2496, you MUST use an external limiter, such as the Innovonics 223. These processors were for use in the studio or announcer booth; the limiter circuit was included in the feed to the transmitter for all inputs. If you neglect this essential component, you will be one of the people complaining about protection trips. If you exceed 100% modulation, the K7DYY trips on protection; its doing its job correctly.

I GET RANDOM NUISANCE SWR PROTECTION TRIPS ON VOICE PEAKS ON MY K7DYY TRANSMITTER. I AM USING ALPHA DELTA ANTENNA SWITCHES WITH AN ARC PLUG LIGHTNING PROTECTOR.

If you are using Alpha Delta Switches with an Arc Protector, and have some SWR on your antenna, remove the Arc Plug. This is not to say the Alpha Delta Switches are not good switches. The Arc Protector is doing its job correctly. When high SWR causes voltage spikes on modulation peaks, the protector fires. Then the K7DYY AM transmitter SWR protection trips. That also is doing its job correctly. Nothing defective in either, they are working as designed. Simply unscrew the brass plug, hold the antenna switch so that the Arc Protector falls out into your hand. Then put the arc protector in a plastic bag stapled to the manual for your Alpha Delta Switch. Put the manual in your filing cabinet for future use. The Arc Protectors will be there for future use, or if you choose to sell the Alpha Delta Switch. For lightning protection, disconnect all antennas when not in use, or whenever you hear thunder or anticipate a storm. This is much better lightning protection than optimism and an Arc Protector. When screwing the brass plug back into the Alpha Delta Switch, just screw it in far enough that the top is flush with the top of the switch case. All of my coax fed antennas have bulkhead style coax adapters attached to ground rods far away from the house, before they attach to the feedline which goes into the radio shack. I can disconnect them there, and roll up the house side of the feedline to keep all the arcs and sparks far away from the house.

If you are getting protection trips from arcing in your antenna tuner or SWR variations from wet open wire line, STOP! Repeated arcing can damage the Super Senior. Diagnose the cause of the protection trips. Just because the failure modes of solid state rigs are not as spectacular as those of a 4-400 with a few kilovolts on the plate, it is not reason to ignore protection trips. Diagnose your problem before you break something.

DO I NEED AN ISOLATION TRANSFORMER?

Absolutely not. This urban legend relates to much older K7DYY Senior and K7DYY Junior models. In certain cases, people encountered problems with connecting PTT and other lines directly to earth ground. This is NOT a problem with the Super Senior. Any modern equipment which employs switch mode power supplies can provide good isolation from the AC line without an isolation transformer. All modern consumer gear uses switchmode power supply techniques which fully comply with UL and VDE safety guidelines. Moreover, you would need a rather large transformer, probably 10 Amp or more to do this, and the expense is not justified. You do not need one for your modern transformerless TV or stereo equipment; you do not need one here either. This comment is also the case with the mike input line; a high quality 600 ohm line transformer can be used, but I directly connect the output of my Behringer equipment to the audio input. NOTE: do not plug or unplug anything, particularly the rear accessory connector, with the AC power on; you may accidentally short pins to the wrong connection as you are mating the connectors. This is just careful operating practice.

I HEARD THERE WERE CAPACITOR FAILURES IN THE OUTPUT RF FILTER; IS THIS A PROBLEM?

No. Again, this applies to the prototype and earliest production runs of the K7DYY 160/80 Super Senior quite a few years back. A heavy duty part was done as a design upgrade to all recent units. This was never a problem with the later 80/40 production run model. Use very low SWR and make sure there are no intermittent connections in your antenna system or transmatch. No solid state equipment enjoys high SWR. There was a brief run of output FETs that had some QC problems from the original manufacturer, but this was not a fault in the K7DYY design. All of this was taken care of under warranty.

I HEARD THERE WERE PROBLEMS WITH THE 80/40 MODEL; IS THIS STILL A PROBLEM?

The prototype and Beta test units did have a problem that was partially caused by feeding too much high frequency audio energy into the mike jack. The internal peak limiter was not fast enough to deal with the problem and had to be improved. I experienced this as an early adopter of this technology, but Bruce corrected the problem. The K7DYY D104 mike processor has been reissued as a Mark 2 model, with a phase rotator, improved noise gate, and most importantly, high frequency roll off necessary to address that problem. The current production K7DYY Super Senior 80/40 model design has also been changed to eliminate that problem when using an external audio chain. See my separate article for data and frequency response curves of the K7DYY D104 mike processor.

Use very low SWR and make sure there are no intermittent connections in your antenna system, switching, or transmatch. I replaced all my cheaper antenna switches with Alpha Delta switches. I did remove the "arc plug" by unscrewing the brass plug and saving the device inside (just in case I wanted it later). If the antenna has significant SWR (for connections after the transmatch), the arc plug will fire on voice peaks with a full legal limit AM or SSB transmitter. This is not a flaw in the Alpha Delta switch or the radio equipment; it is just doing its job protecting against voltage peaks. SWR will increase the voltage above normally expected levels, firing the "arc plug" even on a legal power level. No solid state equipment enjoys high SWR. It may cause trips of the K7DYY protection circuitry if the arc plug fires. Do not allow this to be a common occurance. Fix the problem with the antenna or switching circuitry.

Avoid pushing too much "presence rise" above 4 KHz into the K7DYY Super Senior audio input, particularly the 40 meter model. It defeats the protection circuitry that limits the peaks inside the transmitter. See the photo of my EQ settings; it has a peak at 4 KHz, but the 8 KHz is set to full attenuate (20 dB). This protects the transmitter and avoids an excessively wide signal. When operating on 40 meters at the top of the band, excessive high frequency energy will cause splatter outside the band and invite an FCC QSL card. Most vintage receivers will not hear anything above 5 KHz audio anyway; the commercial AM band uses 10 KHz spacing, which implies a similar upper frequency response. Early production K7DYY D104 processors had no upper frequency limit. They can be very broad. New Mark 2 versions limit the highs to prevent damage to the 40 meter model and avoid splatter. You can watch this on the scope when saying "SSSSS". Early Mark 2 processor boards had a sluggish response on the noise gate; a capacitor change eliminated that, and response is flawless when the mike is keyed. I have provided data on the separate page I have for the mike processor, along with my adjustment of the 100K compression resistor with a 22K parallel resistor, to reduce fan noise, while still providing adequate compression.

See my article on splatter: HIGHLEVELsplatter.html

See W8JI article on splatter and its causes (equally applicable to wide band SSB and AM): http://www.w8ji.com/transmitter_splatter.htm

WHAT ABOUT UPWARD MODULATION? CAN I RUN 120% PEAKS?

If you reduce the carrier, you can run higher upward peaks. Usually vintage receivers will tolerate some upward overmodulation, but as you get to 120%, distortion increases. Wasn't the whole point to have good clean low distortion audio? Of course, with a Software Defined Radio or a Synchronous Detector, it will work fine. I do not favor that much technology. If you are in a net with mixed vintage and modern AM checkins, the Synchronous Detector goes nuts when someone with a DX-100 transmits off frequency a bit. The K7DYY limit is 1500 watts PEAK. You get that when set to 375 Watts carrier and symettrical modulation, which is about what I use (300 W carrier). I just see no point. 1500 Watts is 1500 Watts is 1500 Watts. I favor the KISS principal. Some people report they get as good or better compliments on their audio using a D104 with the K7DYY processor in the base compared to a whole rack full of technology. The new K7DYY D104 Mark 2 processor even has a phase rotator in it.

It is important to realize that the whole concept of 120% upward modulation is an obsolete practice deriving from TUBE AM transmitters. The positive overmodulation allowed you to overcome the power limitations of your plate modulated RF final by stacking on some extra power from your modulator upward peaks. In those days, it worked to provide a marginal added level of punch. The K7DYY is a modern solid state AM transmitter; its PEAK specification limits it to 1500 Watts PEAK, regardless of audio modulation percentage. I suggest that you use a symettrical modulation waveform, and skip the complexities. The K7DYY D-104 audio processor provides a symettrical output, and employs a distortionless phase rotator to reduce the non-symettry in the audio waveform ahead of the compressor. Just use a good monitor scope to set up the D-104 processor and forget it.

MY K7DYY HAS NOT BEEN USED FOR A WHILE. NOW WHEN I TURNED IT ON, THERE IS NO RF OUTPUT

The contacts in the T/R relay have built up some oxide. No damage results from this, the protective circuitry takes care of that. While the transmitter is powered on but in standby mode (both switches DOWN), tune the VFO to the band edge. Cross the band edge, causing the output filter relays to cycle several times, thereby cleaning the oxide off the contacts. The K7DYY Super Senior switches automatically between the two bands when the VFO display shows the lower or upper band, for instance, 80 or 40 meters. Tune back to your favorite frequency and you will see full output when you go to transmit. I have had this occur in my Yaesu FT-950 antenna tuner relays. Just cycle them a few times, and all will be OK again.

HOW MUCH CURRENT DOES THE K7DYY SUPER SENIOR DRAW?

Well that is not a frequently asked question any more. People are used to a full legal limit AM station requiring 240 VAC at 30 or 40 amps, maybe 3 phase. Not this one. Being the anal retentive detail freak, I did a test, just to get the data. I used the popular modern digital "kill a watt" device. It measures line voltage, current draw, wattage, power factor (related to phase of voltage and current), and other things, all in one convenient box. No, you do not need to get your slide rule out and chase a phase vector down a rathole. This data is for a Super Senior 160/80 running on 120 VAC (exactly) at 300 Watts carrier and 100% modulation at 3870 KHz. Standby (recieve): 0.23 A. Carrier, no modulation: 5 A. Full modulation: 6 to 6.5 A. You probably do not care much other than you can run this rig from a standard 15 amp outlet, along with a receiver all your accessories. But I like hard data, so there ya go.


The 80/40 version is a fresh design and production models are shipping NOW with a backlog of orders. Some may not have the real estate for a 160 antenna or may live in the south or west where 160 is too noisy to be of real use. I hope Bruce is able to reach that market with the new addition to his lineup. OK so here is the question: is this a good value for the money? Compare the cost of a fully refurbished Johnson Desk or Johnson 500. There is one ham who advertises in Electric Radio that does a beautiful job restoring them to like mint in box condition. Compare the cost of a KW-1, if you are lucky enough to find one. Compare the cost of a WRL Globe rig. This is a brand new, basically plug and play that delivers better audio than any of those options. I simply had to reduce the amount of parts and racks in my house to make room for some lifestyle changes. I moved three large truck loads of glass tubes, modulation transformers, condensers, power transformers and chokes to a new owner and made some reasonably good swaps including a nearly new treadmill for exercise. I think it was a good move.

AM is a special mode that many of us first fell in love with as shortwave listeners when we were kids half a century ago. Maybe you came into the hobby from CB and were frustrated with the stuff that went on at 27 MHz, but became accustomed to the sound of AM and studied for your ham license. Or possibly you stumbled across an AM QSO and someone helped you adjust your ricebox. You met new friends that you actually had a QSO with, not just swapped signal reports. I still love my Johnson AM equipment and working on it; but to own a higher power rig for this price, I think it all turned out great.

There is another consideration to deal with: Is this still real AM? Many AMrs have adopted highly modified Yaesu FT101s, flex radios or homebrew Class E or other solid state rigs. For our SSB and CW, there are Japanese alternatives to hollow state. The availability of large glass tubes is getting problematic; recently RF parts has been shipping 572Bs from a Chinese manufacturer that actually work, according to rumor. Don and I discussed this in context of fitting two packrats in the same 900 square foot house and the K7DYY AM transmitter was the only real solution that did not result in unacceptable limitations on HF operating style. We made the same decision when we obtained an ALS-1300 solid state linear.

If you are concerned about the cost of a set of finals, consider this. You will need some FETs and 2 gate drivers to replace everything in the final compartment PC board. Both parts are stocked by mouser.com. The FET is Mouser P/N 512-FQPF11N40C and the gate driver is P/N 849-IXDD614CI. Mouser has no minimum order and they charge about $8.00 for Priority Mail shipping. Compare this to the cost of a single 4-400 from a reputable manufacturer. Large glass tubes will be harder to find. The availability of smaller ceramic external anode tubes suitable for amateur power levels will shrink as production focuses on the larger broadcast sizes that are still in demand. This is what the future looks like. Modern AM broadcasters have already made the switch to solid state; get with the program.

It helps if you think of the output FETs as vacuum tubes without an internal pilot light to tell you they are working. For the truly classic (old buzzardly) AM crowd, I offer this: This is an AMERICAN MADE product. It is being sold by the actual engineer entrepreneur who created it. When is the last time you were able to support such a concept? Frankly, whenever I can, I use American made gear. The Ameritron amplifier for my SSB station is an example. I have a Ten Tec original brown front Corsair and OMNI with a Heathkit SB200. My station includes classic Johnson and Hammarlund and other Heathkit equipment, as well as American made test equipment whenever possible, even some classic Techtronix and Hewlett Packard gear.

For other information on purchasing or setting up the K7DYY AM rig, see the following links:

  

73,
Janis
AB2RA
Text size:  +   –      Back to Vintage Equipment
Back to AM Transmitters
Back to the Home Page