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Adding a 6146B stage to my transmitter




 
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Author Topic: Adding a 6146B stage to my transmitter  (Read 2963 times)
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w9jsw
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« Reply #25 on: March 25, 2018, 03:51:13 PM »

OK, Matthew

Added the shunt feed per the article.

John

On edit - whoohoo, just scored an NOS ART-13 mod transformer!

* 811 Transmitter v0.1.pdf (100.97 KB - downloaded 34 times.)
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WA4WAX
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« Reply #26 on: March 26, 2018, 11:06:13 AM »

John:

Two comments:

Use an 812A for RF, and not an 811A.  One 812A will give you about 120 watts of carrier.

Also, an 811 pair is way too much grunt for modulating just one triode.  A pair of 809's would be a better choice, or even a pair of 807's or 1625's in AB service.

Single ended OK if you plan to run only on 160, 80, or 40.  Single ended is bad Ju Ju if you want to run on 15 or 10.

Good luck!
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w9jsw
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« Reply #27 on: March 26, 2018, 01:31:35 PM »

Hi Matthew,

I have been keeping with the pair of 811's thinking I would try to go to more carrier say around 200W. Jack K9ACT updated this design using a 810 and was able to see 225W. Was mostly a drop in except for bumping the DC to 1700V and adding -50v grid bias. Attached is my take on this idea. Did I add the bias correctly?

I will look at some of the other suggested tubes also.

My plate transformer does not have a rating. They guy I got it from thinks it will do around 200ma or a bit more. I was thinking of using it to power the Mod deck only and using another transformer for the RF part. Got my eye on a bigger trans that will do 1700 at around 350ma.

What should I be using for the neutralization cap? His original design had a variable there but this latest design shows a fixed 20pf. I am thinking a variable would be needed if I am using different tubes with different internal capacitance.

How about this one - https://www.rfparts.com/capacitors/capacitors-hammarlund/7254172.html

Also, there is a inductor on the grid. What should I be using there?

John

* 810 Transmitter v0.1.pdf (117.05 KB - downloaded 18 times.)
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w9jsw
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« Reply #28 on: March 26, 2018, 02:09:20 PM »

Hi Matthew,

One more thing - what do you mean by single ended. I only plan to run on 80 and 40. Perhaps 20 in the future. What should I do differently?

John
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WA4WAX
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« Reply #29 on: March 26, 2018, 06:10:11 PM »

Single ended means unbalanced.  Two triodes single ended are in parallel, not push-pull.

It seems to me that an 812A pair in push-pull would fit your needs.  You can even put the beast on 10 meters one day.

About 155 watts of audio will modulate them 100%.

This old article is a nice starting point.


http://n4trb.com/AmateurRadio/RCA_Ham_Tips/issues/rcahamtips0206.pdf


BTW, you can link couple the plate tank circuit to a similar circuit close by.  In fact, fairly close with a shield partition and feed through insulators.  Another option is to mount the two inductors at 90 degrees to one another.  At the end of the day,  the two tank coils can be parallel without a shield if spaced about 3.5 coil diameters or more.  It depends on how roomy your chassis will be.

OK.........The second LC tank will have a somewhat higher L/C ratio, or lower Q.  The LC tank for the tubes needs a Q of about 15 for deep class C.  The second one will be fine with a Q of 7 or 8.

In operation, you tap the second one in symmetric fashion on either side of neutral with your balanced line.  Now, fully mesh the cap on the second one, and dip the plate tank.  Load by unmeshing the cap on the second tank.  Go back and forth between the two.

This arrangement keeps HV off your antenna lead 100%!  It also gives you more harmonic suppression, so no Nastygrams from the FCC.

A good link line would be two pieces of #12 enamel wire, spaced about 1/2 inch.  You will be using 8 to 10 inches at most, with each end connected to the link coils. 

The tap points on the second LC tank will be determined by the load Z presented by your feeders.

If you go single ended with a blocking cap, consider a Pi-L network instead of a Pi.  Again, Q of at least 15 IMHO.

Good luck!
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WA4WAX
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« Reply #30 on: March 26, 2018, 06:21:15 PM »

One last point:

On the first tune up, resonate the plate tank with a GDO BEFORE applying drive!  This will help you to avoid smoke and blue sparks.

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WA4WAX
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« Reply #31 on: March 26, 2018, 06:52:46 PM »

One more:

Forget about the crystal oscillator and multiplier sections.  Just focus on amp and driver.

http://n4trb.com/AmateurRadio/RCA_Ham_Tips/issues/rcahamtips0802.pdf
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w9jsw
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« Reply #32 on: March 27, 2018, 07:58:42 AM »

I like the 0206 design. I think I need to keep this simple, though, to start. I think I will start by breadboarding the 811 modulator. I just need a oil filled cap and a choke to get that going. I can then use it to drive 1 812 to get on the air, but plan to make room on the chassis to mount a second 812 later. The second tube will require me to upgrade my current plate trans to one with more power. I will further keep this simple by only going for 80/40M now, hopefully using the inductors from the above 0206 hamtips.

I have a tendency to keep over-designing/thinking and then lose interest before I get the project on the air. I need to get to a good starting point then plan for a second step later on.

On the balanced output, I guess I get rid of my tuner (with watt meter) and the 1:1 current balun. So I just drive the balanced line directly and use the tank to tune it for best power transfer? How do I measure output power?

My RX will be a SDR that I have. So I can use it in band-scope mode to check for harmonics. It can show the entire 1-30mhz spectrum in one view. Not a spectrum analyzer per. se., but can give me an indication of out of band harmonics.

How can I test the modulator prior to going on the air. Can I put some sort of load on the output of the mod trans and then feed audio into the mic input and measure the peak to peak voltage with my scope? If so, what sort of load and how would I hook it up? There is a lot to do just to get to this point.

John
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w4bfs
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« Reply #33 on: March 27, 2018, 11:17:57 AM »

....I have a tendency to keep over-designing/thinking and then lose interest before I get the project on the air. I need to get to a good starting point then plan for a second step later on....

How can I test the modulator prior to going on the air. Can I put some sort of load on the output of the mod trans and then feed audio into the mic input and measure the peak to peak voltage with my scope? If so, what sort of load and how would I hook it up? There is a lot to do just to get to this point.

John

know what you mean .... I have some projects going from 20 years ago that have been picked up and set down more than once ... however, I think the overdesigning tendency you mentioned is a rare ability and needs to be nurtured while kept in practical check .... new and better methods come from this thinking outside of the 'box'

testing the modulator is a resistor dummy load of near the correct impedance and wattage ... do not drive to full power levels outside of the rated frequency response
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WA4WAX
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« Reply #34 on: March 28, 2018, 03:52:14 PM »

One more thing:

Wind those tank coils with # 12 or #10 copper.  That way, you can use those spiffy DX Engineering coil clips.  They are silver plated, and heavy.  No soldering.  They will glom on to wire as large as #10.  You will want them for the second (antenna match) tank.  Find the best tap point with heavy gator clips, then screw down a couple of coil clips.

Space the coil turns at least 3 wire diameters.  I would likely use 1/4 inch to 5/16 inch of spacing.  If you make a frame, use G10 or Polystyrene.  I would not use PVC as many might do.


Good luck!!!
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w9jsw
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« Reply #35 on: March 29, 2018, 08:20:12 AM »

Still locating parts. I decided to split the power supplies between the RF and Mod decks. Now looking for a choke for the RF side that can handle 400ma or more. 2 - 812 tubes. Found a UTC-S36 swinging choke - 4-20HY. Will that work ok in a shunt choke config or should I be using a fixed choke value in that circuit?

Will the 811's have enough power to modulate 2 812's?

John
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« Reply #36 on: March 29, 2018, 11:01:23 AM »



Going to the well.......

RCA H am Tips  can be found at

N4trb.com

Look for Volume 2 Number 5

The skinny on 811s and 812s.

Do it for the children.

KLC
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WA4WAX
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« Reply #37 on: March 30, 2018, 12:34:56 PM »

One more thing:

If you use an 807 driver stage, use  Sylvania 807W tubes.  They are less likely to scratch and bite than regular 807 tubes IMHO.
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« Reply #38 on: April 02, 2018, 12:39:55 AM »

Still locating parts. I decided to split the power supplies between the RF and Mod decks. Now looking for a choke for the RF side that can handle 400ma or more. 2 - 812 tubes. Found a UTC-S36 swinging choke - 4-20HY. Will that work ok in a shunt choke config or should I be using a fixed choke value in that circuit?

Will the 811's have enough power to modulate 2 812's?

John

The 125W modulation transformer you mentiuoned, may not need a modulation reactor, nor would the ART-13 unit. Most of the smaller units don't need one and are designed to carry the RF stage DC current. But modulators almost always perform better with one. the 4-20H swinging choke is not suitable. If a costly modulation choke is not available, find a smoothing choke with just one inductance value. There's a formula somewhere that gives the inductance needed when the lowest audio frequency and the load resistance represented by the modulated RF stage are specified. Some people have strung smoothing chokes in series to get an overall higher inductance value.
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w9jsw
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« Reply #39 on: April 02, 2018, 07:57:24 AM »

Thanks for the input, I appreciate it. I will try to find that information.

Most of the design conversation has switched to the 8xx mod by 811 thread. Current plan is a single 813 moded by 811's using one supply, with all LC  and interconnect being overbuilt in the event I go to a pair of 813's later.
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WA4WAX
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« Reply #40 on: April 03, 2018, 11:44:17 AM »

I would stick with triodes......a pair of 812A.  At the end of the day, it is your project.

Matt
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Steve - K4HX
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« Reply #41 on: April 03, 2018, 07:00:06 PM »

I'd recommend a single 813 over a pair of 812, unless you just love triode.

1. 813s are more plentiful
2. 813s can produce more power
3. 813s are easier to drive
4. 813s are easier to neutralize.

KISS.
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« Reply #42 on: April 03, 2018, 09:46:50 PM »

Thanks for the input, I appreciate it. I will try to find that information.

Most of the design conversation has switched to the 8xx mod by 811 thread. Current plan is a single 813 moded by 811's using one supply, with all LC  and interconnect being overbuilt in the event I go to a pair of 813's later.

Overbuilt is the word of the wise!
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« Reply #43 on: April 04, 2018, 01:51:48 PM »

The 810 is an awesome triode tube.

FWIW, I think you need more grid bias for the 810 so here is a suggested schematic:


Phil - AC0OB

* AC0OB 810 Final.pdf (33.26 KB - downloaded 42 times.)
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