2x 813 amplifier?

[N2DTS]

I will post some pix tonight.
I have lots of work to do, pulling both power supply decks for the 2x813 AM rig and modulator, and swap transformers, the one in the RF deck will give 3000 volts, the one in the mod deck does 2200 volts under load, so I need to swap them out, I will be using the mod deck power supply to power the amp, and besides changing the iron, need to check the voltage rating of the oil filled caps on the deck.

I also need to install some feed through insulators between the two cabinets, and make up an amp key cable between the flex and the cabinet/ amp.

I also need to slow the amp fan down, its too noisy.
I plan on making a better 80 meter coil, I am using one for the 3x4D32 rig at the moment.

At 200 watts out, the tubes show no color, and the signal sounded very good in the mod monitor.
Four 813's put out a nice amount of heat, so the amp will make a nice shack heater for the winter.


I was a bit surprised at how many good QSO's I had with just 25 watt out.

Brett

[N2DTS]

pix...

[N2DTS]

pix

[K1JJ]

Hi Brett,

The amp looks FB. Nice attention to details and you used quality hardware, OM.

That amp shud serve you for a long time.

One good point is how quiet it will run, since 813's require such minimal air cooling.


BTW, I'm in the process of converting Quadzilla (4X1 linear) over to a class C plate modulated rig using a 4X1 modulated by a pair. Shud have it on in a week or so.  Like you, I'm in the midst of the building fun right now and always good to see others' work for inspiration.

Later -

T

[N3DRB The Derb]

Quadzilla Squared, cum awn. 

[KM1H]

Very nice, it gets my blessing

Carl

[N2DTS]

A 4-1000 modulated by a pair?
Sure you will have enough audio?
You might have to turn it down to 300 watts carrier....

I am starting to scrape the bottom of the parts barrel.
You need to start getting creative unless you want to spend big bux on parts.
I have some stuff set aside for a homebrew CW rig for 80 and 40 meters, a trans receiver of sorts, but dont know if I will ever get going on it, maybe I will when it snows, sure would like to get back into CW.


I was thinking about getting a 3cx1200 type amp and running 220 volts into the shack, but the 4x813 amp should do.

I put a 400 ohm resistor in the fan power and got it so it moves air but is almost silent.
I really like rigs with no fans, the push pull 812a rig was best, no variacs (buzz), no fans, a silent radio.
The 3x4D32 rig has no fans, so its quiet, the 2x813 with 4cx250b modulator has blowers and fans but on variacs so I can slow them down to a low noise level.

The amp is in the rack right next to the operating position, so it needs to be quiet.
I took out the antenna tuner, the 32V3 and homebrew receiver number 1 and put the amp in there, no place to put that old stuff...  4 racks (and no room for more) and a desk full of stuff...

Brett

[W1RKW]

Brett,
Just a safety suggestion; The B+ connection on the outside of the chassis, the HV wire you connect to it, you may want to put some sort of shield or boot on it so you or anyone else doesn't accidentally  come in contact with the exposed metal.

Nice job! And clean too!

[WA1GFZ]

I was thinking the same thing Bob. How about a right angle spark plug boot.

[N2DTS]

All my equipment is like that, but its all in rack cabinets with doors that lock.

I have some amp questions, never having had any, or anything grounded grid....

I get 200 watts carrier out and about 900 to 1000 watts pep at about 2000 volts.
I can load it heavier and drive it less, or load it lighter and drive it more, and seem to get the same results withing a wide range,  what is the best way to run it?

I dont seem to get much of a dip in plate current, but get a nice peak in power output. That seems odd.


I only seem to get about 1100 watts output on ssb, is that low?

I can only seem to get about 1100 watts pep out on AM or ssb, even if I turn it up to 2500 volts.
I suspect I could turn it up to 3000 volts on ssb and get more since the duty cycle is low, but thought I could get more out at 2500 volts....

Brett


 

[WD5JKO]

I get 200 watts carrier out and about 900 to 1000 watts pep at about 2000 volts.
I can load it heavier and drive it less, or load it lighter and drive it more, and seem to get the same results withing a wide range,  what is the best way to run it?

    For AM, I would log the variables and compute the plate efficiency while looking at linearity with a scope. Tune for best linearity at acceptable efficiency. With the Flex 5000 driver I suppose doing Trapezoid pattern would be a challenge? if not, using the Trapezoid is very handy for tuning any form of AM linear or efficiency modulated amplifier. If the exciter is very clean, and a Flex 5000 should be, then maybe modulate with a triangle wave, and use the scope as normal envelope pattern. This might be easier than doing the Trapezoid pattern when adjusting the big AMP.

I only seem to get about 1100 watts output on ssb, is that low?

 Maybe. I wonder how long the coax is between the amp and the Flex 5000 ATU? Without a tuned input to the 813 cathodes, you are likely loading down the drive signal such that every other half cycle is compressed. A tuned input in the AMP, or a very short cable should help. Some of the big AMP builders say that using RG-8 over RG-58 on the input makes a difference when a tuned input is omitted in the amplifier.

That AMP sure looks great Brett,

Jim
WD5JKO

[N2DTS]

I dont think I have anything that generates a triangle wave, I will have to look.
The flex has some built in tests, 2 tone, freq sweep, but I dont think it does a triangle.
Maybe the 2 tone and the spectrum analyzer will show something....

I ran it up to 3000 volts last nite and got about 1600 watts pep out on sideband.

The tuner in the flex gets a good match to the amp, and the coax is rg8x and about 5 feet long, I will try some rg214 between the radio and the cabinet.
I dont think I want to add a tuned input to the amp, as that would make another thing to tune, and I dont think I have space to add a circuit and have it look right, add a switch, etc.
I dont understand why more drive does not do the same thing, more voltage, right?
Drive requirements are quite low, about 10 watts on AM, 30 watts pep on ssb....


The plate current meter seems worthless for tuning up, it basicly does nothing, the power meter is what I have been using, it shows changes in loading and tuning, the meter on the power supply matches the meter in the amp, but they just read about 400 ma at 200 watts carrier, and while you can load it heavier, and play with the plate tuning, it does not change much, other than go up a little bit when you load it heavier....

I wonder if I seperated the various grid returns off ground would improve things, but the design I found on the web did not do that...

I got it all intigrated into the station last nite, and changed the power supply trans, and one cap in the power supply from 3000 volts to 4000 volts so all the caps are good for 4000 volts.

I also did some tests last nite and the xyl did not start screaming about me getting into the TV, I wonder if that will hold up. If it does, I might be able to get on a bit at nite....

Brett

[The Slab Bacon]

In leanyour mode the yamplifier should be loaded heavily enough that you shouldnt see a real large dip at resonance, but you should see something. Try loading it lightly and check your dip. then bring up the loading, and touch up the tuning again after you load it up. Dont forget in leanyour mode, even though you are only running a couple hundred watts of carrier, you have to have it loaded heavily enough to make the audio peaks.. (henceforth the small dip at reduced drive)

Here is another thought I was pondering............... A quad of 813s is still capable of LESS dissipation then a quad of 572Bs (500w vs 640) why not use a quad of 572Bs instead. They are very happy in GG service and will make the same or more power at a lower plate voltage??  (1800-2000V) The 813s are prolly gonna want somewhere around 3000v to get all warm and fuzzy.

Keep in mind that a pair of 813s will easily make well in excess of 1000w PEP in plate modulated service. (IE the K1JJ "Tesla 360")

Just a thought to ponder.......................

                                                      The Slab Bacon

                                                      

[N2DTS]

Well, I have a bunch of 813's, but only two 572b's.

My main rig for the last 25 years has been a pair of 813's which will do 700 watts carrier and off the 2kw scale on the power meter.

I am jumping on the flex bandwagon though, and need some power out of it.
Its just so interesting to use, and it has lots of stuff to play with, you can set the TX bandwidth to whatever you want, 0Hz to 20KHz, or anything inbetween, it has little or no distortion, and can be flat in response and has audio processing built in, with more stuff coming.
I do use it as an exciter for the 813 rig (rf) and use its receiver, which is the best receiver I ever had by far, and for AM, is likely the best you can buy.

Actually, I think they have some sort of subliminal program running that brainwashes you.

I always took a lot of pride in operating an all homebrew station, receivers, transmitters, antenna's, but I got to say, if I had to get rid of all that and just use a flex 5000 and an amp, I would be happy....

Which got me thinking the other day (makes my head hurt) I am 51 years old now, and if I had to move, or wanted to move, what a mess I would have with a basement full of rack cabinets filled with all that iron and worthless homebrew stuff.
No one would want it, even for parts say 20 years from now, and I would have to pay someone to lug it out of the basement and put it in the dumpster.
In 20 years, there will likely be very little interest in tube radio, and there will be a glut of restored vintage old AM gear that no one wants on the market as old farts retire, crap out, etc and have to get rid of the basements full of gear....
Its not like there are loads of teenagers lusting after Johnson equipment....Vintage tube stuff is a dead end...

Brett

 

[WA1GFZ]

I would think you have a low tank Q if the dip isn't deep. Try shorting a turn of the tank coil and see if it improves. Another way to check is measuer the values of the plate and load caps at full power and look up what they should be at the operating Z. (power it down to measure them )
The power going up when you increased the voltage because it could run at a higher Z

[N2DTS]

Yes, I should experiment with the coil.
As it is, I think the plate tuning cap is 3/4 closed.

But, I get a great peak in power output as I tune the plate...it seems quite sharp....

Brett

[KD6VXI]

Which got me thinking the other day (makes my head hurt) I am 51 years old now, and if I had to move, or wanted to move, what a mess I would have with a basement full of rack cabinets filled with all that iron and worthless homebrew stuff.
No one would want it, even for parts say 20 years from now, and I would have to pay someone to lug it out of the basement and put it in the dumpster.
In 20 years, there will likely be very little interest in tube radio, and there will be a glut of restored vintage old AM gear that no one wants on the market as old farts retire, crap out, etc and have to get rid of the basements full of gear....
Its not like there are loads of teenagers lusting after Johnson equipment....Vintage tube stuff is a dead end...

Brett

Don't count us all on that hand.  KE7TRP, myself, a pair of friends in SoCal licensed in the last 6 months...  We ALL love homebrewing and restoring. 

There is also a BUNCH of 11 meter operators that have radios that are museum pieces...  And they are ALWAYS looking for more radios.  I know of someone in the great Northwest that has an entire Johnson AND Collins collection, and they all work.  He chooses to run his Flex, but every radio he has, works, and goes inline at times.

Some of it is attitudinal.  Youngsters get crap from "old timers" because we didn't have to learn CW, the tests are easier, etc.  I have a friend who is now an active amateur that isn't doing ANYTHING different than he did on 11 meters, except using more bands now.  And the big turnoff to him 5 years ago?  The attitudes he encountered tuning as an SWL.  I'm not bashing EVERYONE, but it IS a problem, and one that gladly is slowly dying off (bad choice of words).

Yeah, in 20 years there won't be the market their is for them now, but 20 years ago, we where throwing them in the trash because solid state was all the rage.  People WILL get tired of silicon again, and you STILL have EMP to worry about. 

Remember, Tubes have guidelines, transistors have ratings!  Those of us in the know won't be switching ANY time soon....  Even as it gets harder and harder to find parts (it was MUCH cheaper to build a kilowatt in the 80s, even CHEAPER to build a 10 kilowatt (8 3-500Zs was < 300 dollars in 81), people will still be running these things.

I remember 15 years ago, when the internet was just starting to be useful to the general public (and even then, not many had immediate access to it), that was going to be the end of the mail system, the end of the telephones, etc.  Cell's where a dying breed.

Don't count us 30something whippersnappers out of it, I'll be running iron for YEARS to come.


--Shane

[WA1GFZ]

Those of in the know, know how to design using solid state components that can take a beating.....but tubes are still cool

[W1RKW]

Well, I have a bunch of 813's, but only two 572b's.

My main rig for the last 25 years has been a pair of 813's which will do 700 watts carrier and off the 2kw scale on the power meter.

I am jumping on the flex bandwagon though, and need some power out of it.
Its just so interesting to use, and it has lots of stuff to play with, you can set the TX bandwidth to whatever you want, 0Hz to 20KHz, or anything inbetween, it has little or no distortion, and can be flat in response and has audio processing built in, with more stuff coming.
I do use it as an exciter for the 813 rig (rf) and use its receiver, which is the best receiver I ever had by far, and for AM, is likely the best you can buy.

Actually, I think they have some sort of subliminal program running that brainwashes you.

I always took a lot of pride in operating an all homebrew station, receivers, transmitters, antenna's, but I got to say, if I had to get rid of all that and just use a flex 5000 and an amp, I would be happy....

Which got me thinking the other day (makes my head hurt) I am 51 years old now, and if I had to move, or wanted to move, what a mess I would have with a basement full of rack cabinets filled with all that iron and worthless homebrew stuff.
No one would want it, even for parts say 20 years from now, and I would have to pay someone to lug it out of the basement and put it in the dumpster.
In 20 years, there will likely be very little interest in tube radio, and there will be a glut of restored vintage old AM gear that no one wants on the market as old farts retire, crap out, etc and have to get rid of the basements full of gear....
Its not like there are loads of teenagers lusting after Johnson equipment....Vintage tube stuff is a dead end...

Brett

Heck, when I was 20 or 30 years younger I dreamed of having nothing but solid state stuff. Not sure what change my attitude, maybe it was working with tube audio gear, but that change it.  Then hearing AM'ers talk AM, tubes and iron and homebrewing. Then there was something about seeing a device glow (a good glow not a bad glow).  Tubes being hot are cool!   

[N2DTS]

I did some experiments with the tank coil, no change in the lack of any dip.
I get a nice sharp peak in power output, but loaded light or heavy, no dip at all.

I must be missing something...

The grids are to ground, the current meter is in the filiment return, which should show grid current, the power supply meter should read correctly though.

I will change the meter in the amp to the power supply return terminal and see what I get.

Brett

[WA1GFZ]

Either you left out a couple words or the amp could be taking off

[KC4VWU]

Brett,
        If you get to the point where you can't stand all that old gear collecting dust in the basement anymore, just give me a call. I've got a truck!

Phil

[N2DTS]

The amp seems clean, and no rf in, no rf out, and it sounds good in the mod monitor.
I did not think grounded grid amps tended to have problems with parasitics and so on....
It also works ok on ssb, with no odd stuff going on.

Brett


 

[WA1GFZ]

Maybe your metering is not configured properly and you see grid current plus cathode current.
Sounds like you can crank it higher since you pass the XYL radiated susceptibility test. 

[N2DTS]

That is what I thought, and changed the meter shunt to the power supply return and got a grid current reading, which seemed to not change with tuning.

No rf in, very little plate current. Bias is set at 7.5 volts using diodes in the fil center tap return, a 50 k resistor in standby.
2000 volts on the plates.
Put a watt in, get some current, some power out, no dip at all, but a sharp peak in power out.
Put a little more power in, get more power out, same peak in power out, lack of dip.

I can adjust it so I get 150 watts carrier and 800 watts pep, over a range of loading and power input settings, but at the extremes, peak power falls off, like it should.

I have all the supressor grid directly to ground, the other two grids go to ground through 10 ohm resistors.
I thought it would be best to go to ground, with short paths, rather than cap the grids to ground for rf and put the dc to the fil center tap, which would take the grids current out of the plate current picture.

I checked it on the spec an last nite and it looked ok, seems to work ok, why no dip?
No dip at all, the plate current goes up slightly when the plate tuning cap is moved in one direction, it seems to do nothing in the other direction, output power decreases evenly on both sides of the power peak....
Loading works normal, more loading, more power out, more current.



Brett