NEW Project - 6146B Plate modulated by Hammond 1628SEA and 85W SS Amp

[K1JJ]

The journey starts with the first step....    Destination:  A self-contained, homebrew Ranger III in the Twilight Zone.

For your entertainment, picture below a virgin  Bud 17" wide  X 15" deep  X 6" high aluminum chassis.  It's a rather big chassis for a single self-contained 6146B transmitter, but compare it to a Johnson Ranger and we see it's not THAT big.  Lots of room to mount parts underneath. EZ to work on. The front panel will be about 15" high. FULL metering with four meters; grid current, screen current, plate current, HV.

Large 2400 pF loading cap, large 500 pF tuning cap, tank coil suited for a 300 watt transmitter.  Lots of room and great efficiency.  No need to have loads of fixed caps switched in like the Ranger uses.  Cover 160M to 10M, of course.

Featured will be a 300 mA 800V, Variac variable HV step-start supply to eek out at least 50-60W of AM carrier -  with stud-warrior audio peaks from the Hammond/ SS amp.  It uses three big beer can filter caps of drunkenness.  

The Hammond 1628SEA "mod xfmr" is superb; (over-designed) a single-ended  4/8/16 ohm to 5000 ohm 48 Henry  eleven pounder (rated 20-20,000Hz) that will accept 8 ohm audio from an 85W SS module about the size of a pack of cigarettes.  No Heising reactor needed.  My power transformer for the audio board is big:  +- 35V @ 5A = 175W rated.   I already built a 4D32 version of this rig using a 1642SE Hammond and a Dayton 150W analog audio amp. It is possibly the best sounding [transformer] rig for AM that I own.  So the 6146B rig should be a shoe-in.

I plan to add a DDS VFO for exquisite stability and knowing where the hell am I?

This rig will double as a stand-alone Pissweaker rig at 15-60 watts -  or as an RF driver for my pair of 4-1000As in grounded grid (with regulated grid and screen voltages) linear service.  

The paint scheme will be interesting. I plan to duplicate the two-tone colors  (dark maroon/ gray) and artwork of a Johnson Ranger.  The area where the maroon/brown comes up and circles the Ranger VFO will instead be a plate glass area that displays the 6146B and possible DDS readout.   I may name it  my " Ranger III,"  dunno yet.

Lot's of work yet to do. All parts have been picked or awaiting delivery.

More later....

Are you not entertained?

Tom, K1JJ

[KD1SH]

The primary winding is 5000 ohm; secondary is the 4/8/16. So will you run the transformer backwards - solid state module into the 4/8/16 side and the 6146 B+ to the 5000 ohm side?
Is this audio module something you're building yourself, or a commercial make?
Sounds very cool.

[K8DI]

So, the destructive testing zealot within me is asking…

A 6146B is rated for 65w ICAS in plate mod class C. The plate dissipation is 23 watts.  If you run this at 60w carrier, and have oodles of audio for peak positive modulation, what will give first? Arcing from the instantaneously high plate voltage? Melting from the increased heat? Or will the cathode just give up on giving more electrons and no matter how high the plate peak voltage is, some emission limited point is reached where it just won’t give any more positive modulation?  There’s gonna be some limit some place…will you be seeking to find it? I kinda dare you to put continuous sine-like (asymmetrical tone) waves into it…..

Sounds like fun. Although that tube looks puny on that big chassis!

Ed

[K1JJ]

Hi Bill -

Good questions.


Use this ITEM # on eBay to see the audio board. Just needs +- 20 to 35VAC  CT  to work. All the rectifiers and filter caps on board.  Only $14 for 85W board.
Paste it into the ebay search  window:    143464647535  (the URL is too long)


This is the data sheet for the actual audio chip, TDA7294:  Check out page 20... Notice it has great THD% below 75W but falls apart above 75-85W, depending on 4 or 8 ohms.   That's OK cuz it's just a single 6146B to be plate modulated.

https://www.st.com/resource/en/datasheet/tda7294.pdf


Here are the line of 1628SEA and 1642SE hi-fi Hammond transformers. The 1628SEA is very under-rated at 30 watts and 11 pounds. Probably more like 60W + I would guess.  Or use the 75W version, 1642SE for more $.

https://www.hammfg.com/electronics/transformers/audio/1627-1642


Yes, the "Output/modulation" xfmr is hooked up as you described, 5K to the 6146B and 4/8/16 ohms to the SS audio amplifier.

BTW, I received some time worthy info concerning screen voltage techniques (using a screen to plate resistor vs: a choke and supply) on a class C amplifier.  Let me ask permission to post his comments first...

T

[K1JJ]

So, the destructive testing zealot within me is asking…

A 6146B is rated for 65w ICAS in plate mod class C. The plate dissipation is 23 watts.  If you run this at 60w carrier, and have oodles of audio for peak positive modulation, what will give first? Arcing from the instantaneously high plate voltage? Melting from the increased heat? Or will the cathode just give up on giving more electrons and no matter how high the plate peak voltage is, some emission limited point is reached where it just won’t give any more positive modulation?  There’s gonna be some limit some place…will you be seeking to find it? I kinda dare you to put continuous sine-like (asymmetrical tone) waves into it…..

Sounds like fun. Although that tube looks puny on that big chassis!

Ed

Hi Ed,

Yes, 40 watts output is more like it, as demonstrated by the average Johnson Ranger, but 60 watts @ ~80% class C efficiency  is my a goal.  I always seem to get more power out of my tube projects than the datasheets say.  I've had four 6146s in a class C PDM rig once and it did way more than rated.  That's why I use a Variac and power transformer that will let me experimentally bring up the HV and other parameters until things start breaking. Once that point is reached I can back the rig way down and it will never crap out.

A single 6146B is more for the fun -  and it's cool running a pissweaker. The dB game can be easily played when I switch on the dual 4X1 linear with the 6146B as a hi-fi driver.... :-)

BTW, credit to Jeff/W2NBC who first gave me the idea of using the Hammond xfmr  back a year ago. He also has a working rig using the technique.
And credit to Chuck/K1KW for his suggestion to try the inexpensive PDA7294  audio chip.

You can buy a Hammond 1628SEA from Hawk Electronics drop shipped for $156 plus shipping.

Here is the building of "Summer Breeze"  a 4D32 plate modulated by the big Hammond 1642SE and a 150W Dayton amplifier. My cleanest rig using a "transformer."  It's like Valiant power - 125 watts out all day.  But my series modulated 813 rig is the cleanest of them all.  (transformerless)

http://amfone.net/Amforum/index.php?topic=45973.0

T

[KD1SH]

Some very intriguing stuff. The modules are available on Amazon, too; just ordered myself a couple. There are a few Hammond items I've been meaning to order, and I might just toss a 1628SEA into the order while I'm at it.
Thanks for the inspiration -

[KD1SH]

Yes! Hawk has become my "go to" for Hammond parts: they're cheaper than just about any supplier out there, and they ship like greased lightning.

You can buy a Hammond 1628SEA from Hawk Electronics drop shipped for $156 plus shipping.

T

[K1JJ]

Bill,

There's actually a used 1628SE on eBay for $110 plus $12 shipping.   Older 1998 date code.

https://www.ebay.com/itm/275138284407?hash=item400f850b77:g:bN0AAOSwoNRh8GCm


Funny but the very first rig I ever built back in 1971 was a 6146B plate modulated.   So we've come full circle exactly 50 years later.

Let me know how your progress goes in this project too. This should keep me busy posting here for at least a month or two, including final testing and optimization.

BTW, your screen modulated DX-60 using the QIX circuit sounded very good the other night when we talked on 75M.

T

[K1JJ]

Speaking about naming this rig.... the Johnson "Ranger" name is about a tough, military man.  So keeping in the spirit, how about "Commando?"  It's not used anywhere on a rig and is corny enough to be funny.   Imagine a 50 watt rig being called a Commando.  Like a miniature Poodle named Rex.


T

[KD1SH]

Tom,
  Thanks for the compliment on the DX-60. Like I tell people on the air, I can't take credit for the engineering - it's Steve's genius - I just did the soldering. It is fun to hear people's reactions when I tell them it's a DX-60; the guys who are familiar with the DX-60's stock controlled carrier sound are often amazed.
  My current project is the pine-board transmitter that I posted about a few weeks back. The intent was to perfect that RF deck and then build a modulator for it based on the Hammond H301533 modulation transformer - the one with the "ultra-linear" screen taps - with the modulator circuit based on a "high-fidelity" tube amp right out of the RCA Receiving Tube Manual.
  But now I'm thinking of trying the concept you describe instead. It'll be a slightly easier build than all that point-to-point tube wiring.
  I've never given a name to any of my radio gear, but years ago when I was into building high-powered flashlights, I built a flashlight using an array of high-powered LED's, all mounted on a round aluminum heat-sink that I machined, complete with a cooling fan to dissipate the heat generated by the LED's. My wife named it "Dinosaur Breath" because of the roaring sound of the fan when I turned it on.

Bill,

There's actually a used 1628SE on eBay for $110 plus $12 shipping.   Older 1998 date code.

https://www.ebay.com/itm/275138284407?hash=item400f850b77:g:bN0AAOSwoNRh8GCm


Funny but the very first rig I ever built back in 1971 was a 6146B plate modulated.   So we've come full circle exactly 50 years later.

Let me know how your progress goes in this project too. This should keep me busy posting here for at least a month or two, including final testing and optimization.

BTW, your screen modulated DX-60 using the QIX circuit sounded very good the other night when we talked on 75M.

T

[K1JJ]

Hi Bill,

Cool on the potential plans.  Yes, the concept works very well. I think it may be the most efficient method of running an AM rig except for a PDM rig.  The final runs class C and the SS modulator is running very efficient depending on the amplifier. At 100 watts carrier, the 4D32 barely gets warm (with a quiet muffin fan) and the audio amp is cool. Scale that down to a 6146B final at 40 watts with a class D audio amp and we are freezing in the winter time...


BTW, back in 2007, Stu / AB2EZ had experimented with these Hammond xfmrs and SS audio amps. Check this out:

http://amfone.net/Amforum/index.php?topic=12117.0


You mentioned the RCA tube manual hi-fi amp. That was the first audio amp I ever built. It never worked real well for me on the air, but that was most likely from my inexperience back in 1972.

I'm kinda excited about this 6146B project and plan to do a little each day. The front panel will be here soon, so I can bolt it to the chassis using strong side gussets and that will mark the beginning of serious drilling and blasting.

Keep me updated how your project progresses and I'll do the same.



Definition of "Commando"

1 South Africa

a:  a military unit or command of the Boers

b:  a raiding expedition

2a: a military unit trained and organized as shock troops especially for hit-and-run raids into enemy territory

b:   a member of such a unit

going commando
 *****slang : to wear no underwear***



T

[KD1SH]

These little 85W modules are linear class AB, rather than class D, unless I'm missing something? Looking at the specs, I'm not seeing any switching going on. Some of the adds on eBay do call them "digital", though.

Hi Bill,

Cool on the potential plans.  Yes, the concept works very well. I think it may be the most efficient method of running an AM rig except for a PDM rig.  The final runs class C and the SS modulator is running very efficient depending on the amplifier. At 100 watts carrier, the 4D32 barely gets warm (with a quiet muffin fan) and the audio amp is cool. Scale that down to a 6146B final at 40 watts with a class D audio amp and we are freezing in the winter time...

[K1JJ]

You may be right, Bill!

Somehow I just assumed it was a typical class D Chinese switched amplifier and I would take my chances cuz the THD% looked so good.  

*A friend says that it has a "bootstrap" circuit so there is some switching going on. I'll just have to test it to see.


The Dayton 150W amp that I now use with the 4D32 is a class AB amp too - and as you know, I just love the performance of that rig with the Hammond 1642SE.  

This module will require a heatsink of sorts. No problem. I plan on a small muffin fan to sweep a little air over the 6146B and heat sink anyway.  

We were talking with the guys tonight on 75M. Just as an experiment I want to see how efficient I can make the rig -  and how much power I can get out maintaining big, clean audio.   We'll require very deep into class C, bigger tank components and max HV, etc.  Oughta be fun and may pop a few 6146B tubes doing it...  

Thanks for pointing that out.

T


Features:
• Very high operating voltage range (± 40 V)
• DMOS power stage
• High output power (up to 100 W music power)
• Muting/stand-by functions
• No switch on/off noise
• No boucherot cells
• Very low distortion
• Very low noise
• Short circuit protection
• Thermal shutdown
Description
The TDA7294 is a monolithic integrated circuit in Multiwatt15 package, intended for
use as audio class AB amplifier in Hi-Fi field applications (Home Stereo, self powered
loudspeakers, Topclass TV). Thanks to the wide voltage range and to the high out
current capability it is able to supply the highest power into both 4 Ω and 8 Ω loads
even in presence of poor supply regulation, with high supply voltage rejection.
The built in muting function with turn on delay simplifies the remote operation
avoiding switching on-off noises.

[KD1SH]

  Yeah, I saw that "bootstrap" thingie, too, but there's nothing on the diagram to indicate any clocking or switching devices. But, maybe the manufacturer is keeping some of their proprietary goodies under their hat. In any event, it's a neat little device with some impressive specs, regardless of how they're accomplishing it. And you can't beat the price.
  The neat thing about this little module is that you can just hook it up to an output transformer - no "real" modulation transformer needed - and run with it, without dealing with a maze of 12AU7's; 12AX7's; and 6L6's or whatever.
  There are also some 500 watt class D boards out there, but I think output transformers capable of handling that sort of audio power would be hard to come by. The 1642SE primary is good for 3500 volts DC at 300 mills, so there's a KW DC input to the final PA, but the specs say only 75 watts of audio. Too bad - I could see modulating a pair of 4-250's with that otherwise.

[K1JJ]

I think the Hammond transformers are way under rated. If we use the old TimTron rule that each pound of weight is good for 10 watts, then a 100 watt audio (modulation) transformer is good for 1000 watts, which makes sense to me.    In this case of the 1628SEA, 11 pounds is good for 110 watts.   30 watts seems really under-rated.  Probably these are audiophile pristine music program numbers.  

My 1642SE is really massive for a 75W  rated transformer and 28 pounds = 280 watts.  With the 4D32 rig I saw signs of saturation well past 75 watts of audio from the amplifier.  After all, at 20-20,000 Hz xfmr specs, there is a lot of mass needed to pass 20Hz cleanly.  The average human voice has little energy below 60 Hz.  Though, I like my rigs reasonably clean down to at least 20 Hz if possible.

The tone tests will show what we need to know once the 6146B is built with the 1628SEA lashup.

BTW, speaking of modulating something bigger... I'll bet a pair of big 1642SEs in series parallel could modulate a KW rig.


T

[K8DI]

I think the Hammond transformers are way under rated. If we use the old TimTron rule that each pound of weight is good for 10 watts, then a 100 watt audio (modulation) transformer is good for 1000 watts, which makes sense to me.    In this case of the 1628SE, 11 pounds is good for 110 watts.   30 watts seems really under-rated.  Probably these are audiophile pristine music program numbers.  
T

When considering the weight based rule of thumb, keep in mind that in a regular push-pull audio output transformer (not a modulation transformer) there is no DC magnetization effect, the primary DC is balanced/equal and opposite, having no net DC magnetization to contribute to saturation.  Modulation transformers for push-pull to finals will have DC magnetization in the secondary from the carrier standing current. If you use a mod reactor and a capacitor to couple the audio, this magnetization is gone; a good reason to do it that way at high power levels.  With your single ended audio transformer, it's sorta like a mod transformer...in audio use, the primary has standing DC current like a mod transformer would.

You should probably add the standing power from the carrier DC input to the audio power to see if it really is that much above the weight rule of thumb, it is likely closer than you think.

And then, there's the audiophile part...Nobody builds SE audio amps with tubes except esoteric audiophiles, so response below 20Hz is expected, and with that, the degreee of magnetic saturation is greater, as well..


Ed

[K1JJ]

Ed,

Good points about the single-ended magnetization vs: conventional push pull.   And the DC carrier current effect.   Then maybe the specs Hammond suggests ARE reasonable in the single-ended service we are planning.

I have a friend who built an 807 using the 1628SE and says he can modulate the pants off the 807 with very clean audio, so we should be fine with the 6146B.  At maximum power we will look for the limitations of saturation beginning to appear when sweeping the very low audio frequencies.

So my question is:  If we wanted to modulate a big 500W+ watt rig with the 1642SE or a pair,  would a large inductance mod reactor and coupling cap give us the full use of all the 1642SE xfmr core audio capability?  (using a single-ended 8 ohm amp)

* ahhh...  my aluminum front panel and some parts just showed up.  Time to do a little drilling.     Need to cut four meter holes and viewing window for the mighty 6146B.


T

[K1JJ]

I received the 85 W audio module today.  1/2 the size of a pack of cigarettes. The chip uses the same sil-pad and footprint as a 11N90.

Assuming the chip puts out 60 watts and dissipates 60 watts,  (120W total)  I wonder if I bolt it directly to the large  chassis .... (17" X 15"  X 6" )  will that be enuff heatsinking for 60W or will I need a finned heatsink up on top too?  I also have a quiet 4.5" muffin fan that will be blowing air past the chip heatsink and onto the 6146B glass.

I found an inexpensive metal shop in town to CNC  plasma cut my front panel holes for the meters, viewing window and DDS readout.  Big PIA to do it myself.  The rest of the metalwork is a breeze in my cellar.

T


**  Below, as motivation, is the dedicated amplifier that the 6146B rig will be driving. [when needed]    "Commando" driving "Rico Suave."  The amplifier will be very efficient running in class C for AM linear use.  Notice the "Class C" bias selection on the front panel.  Classic old school rigs!

A thread about running a more efficient linear amp on AM:
http://amfone.net/Amforum/index.php?topic=32635.0

[KD1SH]

  So how would we connect for this? Primary would be easy: two 16 ohm windings in parallel to make 8 ohms, or two 4 ohm windings in series to make 8 ohms, etc, but what about the secondary? Two 5000 ohm windings in series would give an unrealistic 10K to the final PA, while two in parallel would give a somewhat more acceptable 2500 ohms.
  I'm looking at this primarily as an exciter-class rig, but it's tempting to ponder how it would scale up. A pair of 1642SE's wouldn't be cheap, but good "real" mod-iron isn't dropping out of trees these days.

BTW, speaking of modulating something bigger... I'll bet a pair of big 1642SEs in series parallel could modulate a KW rig.


T

[K1JJ]

Hi Bill,

It would be best to experiment as I have done to find the best taps on the 1642SE xfmr.  But what you described at 2500 ohms would probably work well. There is a lot of versatility with all those primary and secondary combinations.   When I was testing mine, it was clearly obvious by the audio tone peaks tests which set of taps were correct.

T

[KD1SH]

I think that when all is said and done, the ratios count more than the actual values, anyway. The proof would be in the tone testing, like you say.

Hi Bill,

It would be best to experiment as I have done to find the best taps on the 1642SE xfmr.  But what you described at 2500 ohms would probably work well. There is a lot of versatility with all those primary and secondary combinations.   When I was testing mine, it was clearly obvious by the audio tone peaks tests which set of taps were correct.

T

[K1JJ]

I think the rule is to try to use as much of ALL the windings as possible.  IE, the best power transfer for the given iron should be all of the primary and ALL of the secondary working at one time to be ideal.

In my case, I found that all of the secondary  (5K)  and the (8 ohms) of the primary was best. The 4 ohms popped the breaker on the  SS amplifier in the bridge mode.    16 ohms worked but with lower peaks and earlier peak saturation.

T

[Opcom]

Hi Bill,

Cool on the potential plans.  Yes, the concept works very well. I think it may be the most efficient method of running an AM rig except for a PDM rig.  The final runs class C and the SS modulator is running very efficient depending on the amplifier. At 100 watts carrier, the 4D32 barely gets warm (with a quiet muffin fan) and the audio amp is cool. Scale that down to a 6146B final at 40 watts with a class D audio amp and we are freezing in the winter time...


BTW, back in 2007, Stu / AB2EZ had experimented with these Hammond xfmrs and SS audio amps. Check this out:

http://amfone.net/Amforum/index.php?topic=12117.0


You mentioned the RCA tube manual hi-fi amp. That was the first audio amp I ever built. It never worked real well for me on the air, but that was most likely from my inexperience back in 1972.

I'm kinda excited about this 6146B project and plan to do a little each day. The front panel will be here soon, so I can bolt it to the chassis using strong side gussets and that will mark the beginning of serious drilling and blasting.

Keep me updated how your project progresses and I'll do the same.



Definition of "Commando"

1 South Africa

a:  a military unit or command of the Boers

b:  a raiding expedition

2a: a military unit trained and organized as shock troops especially for hit-and-run raids into enemy territory

b:   a member of such a unit

going commando
 *****slang : to wear no underwear***



T

[/quote]


slang for electronics gear: to use no fuses

[K1JJ]

I'm taking my time with the Commander.   A little each day. No rush.  Actually the hardest part for me is cutting out and filing out all the big panel holes.    Please don't judge this project for looks until I clean all the parts, shine the chassis and sand and paint the front panel. The various panel cuts need a little more straightening with the file too.

The CNC plasma guy couldn't convince me that the holes would be nice and straight (or round) so I suffered and did them all myself using a drill, saber saw and file for the rectangles or hole saw for the meters. What a job. They will clean up FB.

But we're off to a good start. Can't turn back now.  The side gussets (side rails) are fitted and the panel is stiff. Shown is the Hammond 1428SEA audio transformer and the 85 watt module.  I have a big hank of Teflon wire for the wiring job. No plasdick wire in my shack! Notice the big tank coil. It figures out to be perfect to cover 160M with a Q of about 12.  Lots of room in there! I am expecting big things from the efficiency of the 6146B final, maybe 85%, so the tank is big and the bias will be very deep into class C.

Most of the missing parts have arrived so I have no excuse to linger on.

Next I'll lay out the parts and see where everything will be mounted....

More later...

T

[K1JJ]

The Commander awaiting birth like a Frankenstein movie: