ART-13 tuning

[W9BHI]

I have the ART-13 just about ready to go on the air.
I see one article saying you need 2000Pf on the "C" terminal to tune 75 meters,
and I see another saying 300Pf for tuning into a 50 ohm load.
Mine tunes up with no cap but the plate current seems low at about 100Ma.
Power output is 140 watts carrier, with audio it swings to 610 watts.
Contols "A"&"B" are tuned for 3885 Khz.
Control "D" is at 50, control "C" is at 4, control "E" is at 190.
Does this sound correct?
This is my first ART-13 so be gentle on me
Thanks,
Don W9BHI

[W9BHI]

No Takers?

W9BHI

[KM1H]

Hard to say anything since you didnt specify the antenna and VSWR.
I believe I used a 450pf 7500V doorknob that was handy for testing at 3500 into a dummy load but for actual operating it is used only on 20 and 17M.

Carl

[kb3ouk]

They were designed to put out about 100 watts, so the 140 is actually pretty good if you don't feel like pushing it. What voltage are you running?

[W9BHI]

I am presently running it into a Array solutions Powermaster meter and a 1Kw dry dummy load .
VSWR is 1:08 to 1 with 143 watt carrier on 3880 Khz.
Power supply is 1250v plate and 385v screen.
I will be using a tuner and antenna combo that is already tuned on freq.

Thanks,
Don W9BHI

[w1vtp]

I am presently running it into a Array solutions Powermaster meter and a 1Kw dry dummy load .
VSWR is 1:08 to 1 with 143 watt carrier on 3880 Khz.
Power supply is 1250v plate and 385v screen.
I will be using a tuner and antenna combo that is already tuned on freq.

Thanks,
Don W9BHI

If you have it working OK on a dummy load @ 50 ohm Z then plan on using a tuner.  I don't think you will need anything else.

[kb3ouk]

How can you be getting 143 watts out at 1250 volts 100 ma? That's 114% efficiency.

[W9BHI]

I am wondering about the accuracy of the plate current meter.
There is a 12.5 ohm resistor in the power supply - HV lead and it may be rescaling the meter
So the plate meter may be reading low.

W9BHI

[W9BHI]

After reading up on the different power supply descriptions, everyone uses a different value meter shunt.
ALSO the numbers on the meter scale are not miliamps but just a reference number.
That's why I thought it was reading 100Ma. Duh!
That said, I actually have NO idea what the plate current really is.
I will connect my digital current meter in series with the - side of the HV supply and find out what the current really is and then come up with a value of shunt resistor to try and make the scale on the meter somewhat useful.

Don W9BHI

[kb3ouk]

813 data sheet says 1250 volts at 150 ma will give 140 watts, that's with 300 volts on the screen though, too.

[W9BHI]

Looking at the dynamotor power supply they are using a total of 20.1 ohms for a meter shunt.
Down in the right hand lower corner of the panel meter it says "F.S. = 1M.A."
So 20 ohms should give a reading of 200Ma. full scale which is what the meter scale has on it.
I have a 21.5 ohm resistor (what I had available) installed for the shunt.
Current shown is 170Ma, plate voltage is 1286v, screen voltage is 386v, wattmeter shows 150 watts into 50 ohms.
Sound about right?
Don W9BHI

[W6TOM]

 Loading my ART-13's, I have two ART-13's and an ATC, on 75 meters into a 50 ohm dummy load I get as much as 150 watts running off a dynamotor, DY-17A. Power is measured with a bird 43 watt meter and a 250H element. The plate current was dipped, very slight dip, with the radio in tune position. I have NO capacitance to ground off board the radio, I do know others who have told me they have had to add an off board capacitor to get the radio to put out power in the area of what I get. All of mine vary a bit from radio to radio and 120/130 watts is probably average.

 I think that there are variances in the loading circuit from radio to radio plus some have been modified by previous owners. I used the ATC set tonight, on 3985 it will load to 150 watts into a 50 ohm load. My coax fed, with a balun, fan dipole 80/40 meters is not exactly resonate  at 3985 so I get 100 watts out into the dipole with 20 watts reflected.

 Looks to me like your radio is working OK far as power output. The metering on these were designed to be a relative indicator for ease of operation.

[w1vtp]

Looking at the dynamotor power supply they are using a total of 20.1 ohms for a meter shunt.
Down in the right hand lower corner of the panel meter it says "F.S. = 1M.A."
So 20 ohms should give a reading of 200Ma. full scale which is what the meter scale has on it.
I have a 21.5 ohm resistor (what I had available) installed for the shunt.
Current shown is 170Ma, plate voltage is 1286v, screen voltage is 386v, wattmeter shows 150 watts into 50 ohms.
Sound about right?
Don W9BHI

If you are using a higher than required plate shunt resistor, that would explain the higher than actual plate reading.  Simple solution: use ohm's law to figure out the needed 20.1 resistance EG:

R2 = (R1 X RT) / (R1 - RT)

Where R1  = 21.1, Rt = 20.1 ohms  a 424.11 ohm resister across everything will make Rt dead on.  You can use a digital ohm meter and go through your part bin and pick one close and you'll be close enough.  I've included an Excel spreadsheet to help.  input data only in the yellow field

Al

While I was at it I included the formula the other way:

RT = (R1 x R2) / (R1 + R2).

[iw5ci]

I have 2 art-13, i have more than 100w in 80 meters without any caps either on dummy load and a dipole.

[W9BHI]

Thanks Al,
I don't have a 424 ohm resistor in the junk bin.
I am going to order a 20 ohm 4 watt 1% WW resistor along with some other stuff tommorrow from Mouser.
I have just finished recapping the modulator deck.(it probably didn't need it)
The audio is strong but definitly lacks the lows.
I guess that's the way it was designed.

Thanks to everybody who chimed in with ideas and help.
I hope to have this thing on the air this week.

Don W9BHI

[wa3dsp]

I don't have an ART13 but something doesn't sound right about 20 ohms. Is that a shunt? When you calculate the shunt the meter resistance comes into play.

    Rs = Rm / ( Is / Im)   where Rs is the shunt resistance, Rm is the meter resistance, Is = shunt current, Im = meter current

So  Rm/(.2/.001)  would be the formula. If you assume it is a 200 ohm meter then it would be 1 ohm.

Maybe they have some series resistance to the meter off of a larger value shunt?

[W9BHI]

If you look at the schematic, there is a 4k resistor in series with the + side if the meter.
The meter itself is 51.5 ohms. (total meter imp. is 4051.5 ohms).
There are 13.4 and 6.7 ohm resistors in series in the dynamotor power supply for the plate current shunt.

Don W9BHI

[KB2WIG]

The ARTs are designed to load into an aircraft antenna. Short antennas and "Wierd" Zs.



KLC

Dont trust me, I desmoked  2 of 'em.

[wa3dsp]

Don,

 OK that answers the question. The series resistance makes all the difference.

[w1vtp]

Thanks Al,
I don't have a 424 ohm resistor in the junk bin.
I am going to order a 20 ohm 4 watt 1% WW resistor along with some other stuff tommorrow from Mouser.
I have just finished recapping the modulator deck.(it probably didn't need it)
The audio is strong but definitly lacks the lows.
I guess that's the way it was designed.

Thanks to everybody who chimed in with ideas and help.
I hope to have this thing on the air this week.

Don W9BHI

Don

Take a look at your shunt value: I did the math for 21.1.  Your shunt is actually 21.5 ohms.  If the shunt is actually 21.5 ohms the required value is 308.7 ohms.  If you don't have Excel anyone can run the numbers - you can do it on a calculator using the formula I posted.  I'm not speaking as an authority on the ART13.  But the math stands as correct.  Good luck - that plate current needs to be reasonably accurate

Al

[W9BHI]

I think a 20.0 ohm 1% resitor should be close enough to 20.1 ohm.
The meter should read within a few Ma's.
Close enough for government work
Thanks,
Don W9BHI

[KA2DZT]

The meter from the ART-13 measures about 55 ohms meter resistance and is a 1ma movement.  Seems that the meter shunt should be about 0.25ohms.  199 ma flows through the shunt and 1 ma through the meter.

Quick figuring, the meter shunt resistance should be about 1/200 the meter resistance.

Fred

[W9BHI]

The meter has a 4k resisistor in series with the + lead before it connects to the meter selector switch.
Check the schematic.

Don W9BHI

[wa3dsp]

Yes, that calculates to 20.2527 ohms with the numbers you gave me. None of this is an exact science. The analog meter itself is probably no more than 5% accurate. If you really want precise accuracy at the operating current make the 4K a variable or replace it with a 3K and a 1K pot in series then make the shunt slightly high by an ohm. Adjust the pot to the correct reading at the working current. I think you said your shunt was already a bit high so that would work.

Of course you need to temporarily insert and accurate digital meter to use as a calibration device. In the end it will only be as good as your calibration device.