Is series modulation "efficiency" modulation?

[KD1SH]

  Thanks, Rick, for the link - I remember Clark saying that there was a website, but I must have forgotten to write it down.
  Very impressive indeed! I particularly like the fact that it's got both a limiter and a clipper. Right now I'm running a DBX-286S with my AM rigs, and while I absolutely love it - particularly the HF and LF "detail" enhancer - I wish it had a limiter and clipper.

Yes Bill, that is the audio processor we are working on.  Thank you for expressing your interest.
I have been spending many hours revising the circuit layout based upon feedback we have received from folks using the prototype.  In addition to Clark, there are four or five people who have built the kit and are testing it and providing more input.  

Right now I am almost finished with the artwork QC, and expect to send gerbers for new PCBs in a few days.  We have gone to a proprietary microphone preamplifier chip instead of using the typical dual audio op-amp, to reduce standby noise to an absolute minimum.  The processor has a feature we call a "Gain Gate", which monitors voice level, and when the operator pauses, it holds the compressor gain, preventing the amplification rise that would normally occur when there is no input from the microphone.  But even with this feature, we want to make the microphone preamp as clean and quiet as possible.  

We have been working on the design for almost two years, and after the fourth board revision, we think we can make version five a winner.   If you would like more information on this endeavor, feel free to visit:

internetwork.com/MAX/

Availability of version five will be posted there in the near future.  Thank you again for your interest.

[KD6VXI]

Gotcha on the negative pressure diff.  We don't typically have that issue here in the left coast.  Almost everywhere I've worked at or lived we have the heater in the attic.

Problem with utilizing exterior air in the loop is moisture.  I've seen a couple TX that where decommissioned that the blower wheels where starting to rot, metal was rusted out, etc. from using exterior non-conditioned air. There is a reason well heeled radio stations used AC or chiller units!

Winter time seems you have the best option.  Summer, maybe it won't be an issue?

--Shane
KD6VXI

[VE7RF]

Hi Rick,

FB on the blower noise precautions using the 3CX-3000A7.  I once used one but it's fin structure was one of the louder external anode wind-noise generators I've used.  In fact, mine even whistled a bit due to air/mechanical resonance of some kind.    They do need a good robust air flow if not only for the filament power and idle current. (and talking real fast and short...  )  You will be generating your share of heat in class A feeding those 304TLs.

My solution for my present big linear was to slow the blower down with a Variac and get the blower rebuilt at a motor rebuilding shop for new bearings.  I was down maybe -30 DB at best for on-air S/N.  It needed a noise gate on ssb.  That is not good enuff on AM but OK on SSB.  Baby Blue will be real quiet but not the bigger linear amps.  The class C plate modulated rigs are all OK for reduced noise on AM with the class C RF finals and class B modulators being in the middle of the road for heat.

I even looked into an acoustic barrier of glass and other materials, but the only real cure would be putting the big noise offenders into a different room with wall insulation like Ken/W2DTC did with his 3X3 rig. He has his in the garage and his signal is dead quiet in the background.  

T


This pic shows Ken's garage installation from pics he posted on the web.. It is loud and sounds very FB with excellent audio and a quiet background. I especially like the wheels for servicing:

The  cooling requirements for a 3CX-3000A7  can be  greatly reduced IF the  ambient air intake temp is below  40 deg C  (104F).

The  67  cfm  @  1.2"   is  for  40 deg C.  (  104 deg F)
That drops to 56 cfm   for  30 deg C ( 86 deg F)
down to 51 cfm  @  25 deg C  ( 77 deg F)
Down to 47 cfm  @  20 deg C  (68 deg F)

The above is for  4000  watts  CCS anode diss.   Nobody is running anywhere near  4 kw ccs diss.  Even with 5 kw out, anode diss is only  2.4 kw...(68%  eff on 160-40m,  5 kv under load @ 1.5A).  So  actual air requirements are  even lower....much lower. (36  CFM for 2.5 kw CCS diss...with 40 deg C (104 deg F) intake air.

Drops  to 30  cfm  @ 30 deg C  (86F)
down to 27.5  cfm  @  25  deg C  (77F)
Down to 25  cfm  @  20  deg C  (68F).

A Dayton blower,  model  6DKY9  will  easily  do  80  CFM  @  1.2".   It's speed can be reduced  with a small variac, etc.
https://www.grainger.com/product/DAYTON-OEM-Blower-6DKY9

[K1JJ]

Yep, the Dayton blower has a great reputation for doing the job.

I tried to find one for my own big amp years ago but they were never available used on eBay and the new price was $300 to $600+... ridiculous.    But the current Grainger listing for $118 is quite a good deal.  I earmarked it for future use. A Variac to slow them down somewhat works well. I don't remember the actual Dayton model, but it was popular with BC stations and the big amp builders. The 6DKY9 looks ample enuff.

I once drew cooling air from a blower outside the house.  During the winter at 20F it was amazing to feel the tube air outlet at luke warm during full strap.  But the moisture eventually caused its effects.  Presently I rarely use a linear for AM. My AM rigs are all class C and the modulators p-p class B. This makes a big difference in managing air noise and heat.

T

[DMOD]

  Wondering, pondering, cogitating: in traditional plate modulation, we vary the voltage on the plate; the plate current changes - per square law - and we can tune and load in the traditional way since the output resistance of the tube remains the same under modulation. In traditional "efficiency" modulation, as in screen modulation, we alter the current flowing through the tube but the plate voltage remains the same, hence it doesn't follow square law and thus the effective output resistance swings all over creation, so we have to load the output differently.
   Okay so far, but what about series modulation? With the series modulating tube "south" of the PA cathode - between cathode and ground - we modulate the current flowing through the tube by effectively modulating the series resistance, while leaving the plate voltage alone. Cathode voltage on the PA swings with reference to ground, but it's not cathode modulation because the control grid is referenced to the cathode. Reference the control grid to ground and it would be cathode modulation.
   With the series modulating tube above the PA plate, the plate voltage would seem to be modulated, since the series resistance between the plate supply and the plate is being modulated. But, I'd always assumed that the choice of putting the series tube above or below the PA tube was pretty much irrelevant other than considerations regarding what parts of the circuit you want to "float".
   I got to thinking about this because I like both series and screen modulation, and made an assumption that series modulation would have an advantage over screen modulation in that you wouldn't have to do any fancy footwork with the loading control to get full modulation, like you do with screen modulation. But then I started to second-guess that assumption.

Here is a suggested Cathode Modulated 809 circuit using a MOSFET.


Phil - AC0OB

[w8khk]

  Thanks, Rick, for the link - I remember Clark saying that there was a website, but I must have forgotten to write it down.
  Very impressive indeed! I particularly like the fact that it's got both a limiter and a clipper. Right now I'm running a DBX-286S with my AM rigs, and while I absolutely love it - particularly the HF and LF "detail" enhancer - I wish it had a limiter and clipper.

Yes Bill, that is the audio processor we are working on.  Thank you for expressing your interest.
I have been spending many hours revising the circuit layout based upon feedback we have received from folks using the prototype.  In addition to Clark, there are four or five people who have built the kit and are testing it and providing more input.  

Right now I am almost finished with the artwork QC, and expect to send gerbers for new PCBs in a few days.  We have gone to a proprietary microphone preamplifier chip instead of using the typical dual audio op-amp, to reduce standby noise to an absolute minimum.  The processor has a feature we call a "Gain Gate", which monitors voice level, and when the operator pauses, it holds the compressor gain, preventing the amplification rise that would normally occur when there is no input from the microphone.  But even with this feature, we want to make the microphone preamp as clean and quiet as possible.  

We have been working on the design for almost two years, and after the fourth board revision, we think we can make version five a winner.   If you would like more information on this endeavor, feel free to visit:

internetwork.com/MAX/

Availability of version five will be posted there in the near future.  Thank you again for your interest.

Bill, unfortunately family and medical issues have significantly delayed the development of the new All-in-one MAX Audio Processor.   The good news is that the gerbers were sent to Shenzhen the end of last week, and the board manufacturing was completed on Sunday.  The copper-layered fiberglass artwork is now somewhere above the pacific pond, and will be arriving in Georgia sometime later this week.  With several hundred individual components on the PCB, it will take some time to populate an complete stand-alone and on-the-air validation of many significant updates.  Once those tasks are completed, I will be making more information available to all those folks who are interested.

[KD1SH]

Rick, thanks for the update; I truly hope all is well regarding family and medical issues!
I keep meaning to contact via the website regarding specifics that are more appropriately discussed there, like pricing and all that, but something else always comes up. I am very interested and looking forward to getting more information.

Bill, unfortunately family and medical issues have significantly delayed the development of the new All-in-one MAX Audio Processor.   The good news is that the gerbers were sent to Shenzhen the end of last week, and the board manufacturing was completed on Sunday.  The copper-layered fiberglass artwork is now somewhere above the pacific pond, and will be arriving in Georgia sometime later this week.  With several hundred individual components on the PCB, it will take some time to populate an complete stand-alone and on-the-air validation of many significant updates.  Once those tasks are completed, I will be making more information available to all those folks who are interested.

[KD1SH]

Looks like a fun board to build. All thru-hole - it's been many years since I've populated a thru-hole board that size. Pretty much everything I do at work is SMD.

[w8khk]

Looks like a fun board to build. All thru-hole - it's been many years since I've populated a thru-hole board that size. Pretty much everything I do at work is SMD.

Bill, we very much appreciate your interest in this project.  We will not be putting anything new on the web until we run it through its tests and make sure it is ready for prime time. 

Thanks also for the well wishes.  By the way, it does have just ONE SMD chip, just to keep you feeling comfortable.  Perhaps in the future we may produce an all-SMD version, with the components applied by the PCB fab facility, but right now, the through-hole gives many folks the opportunity to put it together and take pride in their accomplishments; it also has lots of options for customization, which would not be quite as open with SMD. 

It is not really a kit in the Heath or Elecraft sense, as there are no step-by-step instructions for each individual component.  But the instructions do group all the tasks to make them run smoothly, and a spreadsheet of all the components is used to easily populate all the resistors, capacitors, etc.  Sorted by component value, it is very easy to insert and solder all like values as a group, so it does go quickly without undue stress.

If you would like more details or have specific questions, use PM or email; I am good on QRZ, and we can even use the landline (cell) if need be.  We will post on the forums when new information is available on the web.

73, Rick

internetwork.com/MAX/

[KD1SH]

   Rick, personally I think that making the board thru-hole is fine business; many hams are vastly more comfortable with it, and it makes modding easier. I'm comfortable with either, really. Everything I scratch-build at home, out of necessity, is thru-hole, since putting SMD parts on a regular proto-board is problematic, and spinning SMD boards for one-off projects isn't practical. Maybe someday I'll try that, though: prove out a circuit on a breadboard; have a board-house spin up  five or ten boards or so, then keep a couple for myself and try to sell the remainder at hamfests.
   For those who've never done any SMD work, it's not nearly the horror that you'd think, at least as long as you keep the parts on the large side; 1206 resistors and caps, and even 0805's, are a breeze with only modest optical assistance, like the standard magnifier lamp, or even with naked eyeballs - my eyes are sixty-four years young, and I can solder the larger SMD parts by eye with no problem (although I prefer the scope). The larger pitch IC's are fine, too; many small signal FET's and bipolars, and diodes, are available in SOT packages that are easily manageable under the magnifier lamp.
   SMD can be faster, too; put a dab of solder on the pad, stick the part on with the tweezers and hit it with the iron, and you're done, no messing with lead-formers and then making sure the part doesn't fall out when you turn the board over to solder the other side.
   Sooner or later, for better or worse, SMD will be forced on us all; I'm finding it increasingly difficult to find the parts I want in thru-hole packages.

Bill, we very much appreciate your interest in this project.  We will not be putting anything new on the web until we run it through its tests and make sure it is ready for prime time. 

Thanks also for the well wishes.  By the way, it does have just ONE SMD chip, just to keep you feeling comfortable.  Perhaps in the future we may produce an all-SMD version, with the components applied by the PCB fab facility, but right now, the through-hole gives many folks the opportunity to put it together and take pride in their accomplishments; it also has lots of options for customization, which would not be quite as open with SMD. 

It is not really a kit in the Heath or Elecraft sense, as there are no step-by-step instructions for each individual component.  But the instructions do group all the tasks to make them run smoothly, and a spreadsheet of all the components is used to easily populate all the resistors, capacitors, etc.  Sorted by component value, it is very easy to insert and solder all like values as a group, so it does go quickly without undue stress.

If you would like more details or have specific questions, use PM or email; I am good on QRZ, and we can even use the landline (cell) if need be.  We will post on the forums when new information is available on the web.

73, Rick

internetwork.com/MAX/

[w8khk]

The boards were not lost while traversing the Pacific Pond.  Time to sniff some solder smoke and do the final QC testing.   Stay tuned!

There will soon be updates here:

www.internetwork.com/MAX/

[KD1SH]

Very nice looking board, Rick. Curious: you fan-out the traces from the SOIC-14 to plated thru-holes; is that for easy access to the inputs/outputs of the chip? Would something like a Berg header go into those PTH's for some reason, or maybe a DIP socket just in case someone came across a thru-hole version of the chip?

[w8khk]

Thanks for the kind words, Bill.

Some folks may not want to solder in the SMD chip, but it is really not that hard.  We can either install the chip on the board for them, or a carrier may be plugged into a couple Dupont 7-pin female headers to address that concern.  I have a couple of the DIP versions of the compressor chip, but the spacing between the rows is too wide to handle that option. I suppose a carrier could be made for a through-hole DIP, but the SMD is less expensive.

It is also very handy to have easily accessible test points for the chip, not only after assembly, but it makes it very easy to verify the pins on the SMD  are properly soldered to the pads during assembly. 

None of the calibration procedures require measurements at the chip, but for troubleshooting it is much easier to place a probe in the through-hole than to balance it on one of the chip leads.  At my age that is almost a necessity!

Later on, we may shrink the board and go all-SMD, but right now that kinda takes the joy out of the kit-building experience.

[KD1SH]

  I would say stick with thru-hole until component availability forces the change to SMD. You'll most certainly sell more kits that way, and space saving isn't really a big concern with this sort of station accessory.  A while back I built a 2 meter transverter as a kit (Down East Microwave). It was all SMD, but for VHF stuff there's a definite advantage with SMD.

Thanks for the kind words, Bill.

Some folks may not want to solder in the SMD chip, but it is really not that hard.  We can either install the chip on the board for them, or a carrier may be plugged into a couple Dupont 7-pin female headers to address that concern.  I have a couple of the DIP versions of the compressor chip, but the spacing between the rows is too wide to handle that option. I suppose a carrier could be made for a through-hole DIP, but the SMD is less expensive.

It is also very handy to have easily accessible test points for the chip, not only after assembly, but it makes it very easy to verify the pins on the SMD  are properly soldered to the pads during assembly. 

None of the calibration procedures require measurements at the chip, but for troubleshooting it is much easier to place a probe in the through-hole than to balance it on one of the chip leads.  At my age that is almost a necessity!

Later on, we may shrink the board and go all-SMD, but right now that kinda takes the joy out of the kit-building experience.