ART-13 filament issue

[KC2TAU]

Yes, it is. Right in the middle. I'm just curious as a lot of folks are saying they manage 125w + with some even saying 175w is possible though I'd imagine this is with B+ in the 1800v + range.

[N8ETQ]

Straight up  "Schwinng". I think my LV is at around 425 or 450.
whats yours?

/Dan

90W is normal at 1300V. How is your grid current? In the paint?

[Bill, KD0HG]

I assume that you're using an external loading capacitor..?
The exact value is somewhat touchy if you want maximum output, I use a 560 pf on 75 and maybe 100 pf on 20. If you have a broadcast variable, hook it up and tune and load for maximum smoke. You would be alternately tuning control D and adjusting loading with the external variable. Also try values for controls E and C. With 1100-1200 plate volts and a good 813 you should be able to do 150 watts out on 80. A friend got nearly 250 watts out of his ART-13 with near 2 KV...And he needed a hell of a blower on the PA compartment..IIRC he ran it without the top cover, too.

Bill

[KC2TAU]

Straight up  "Schwinng". I think my LV is at around 425 or 450.
whats yours?

/Dan

90W is normal at 1300V. How is your grid current? In the paint?

Loaded or unloaded? My supply sits at 385v loaded and 450v unloaded. Is that too low?

Bill,

I am using what appears to be a three gang 365pf per section air variable. The three gangs are wired in parallel. I need to verify that the capacitance is as such, though. I'm going to try and find a better variable as this one that was supplied with it looks like it came out of a receiver. I have two spare 813's and so I'll see if they fare better.

[W7TFO]

Pete,

How do you run a three-gang variable in series?

73DG

[KC2TAU]

Pete? My name is Mike. My mistake, I meant in parallel.

[W7TFO]

Sorry Mike, good drugs here I guess.

73DG

[KM1H]

Im running 1300V on mine and a HB PS that runs other voltages high enough to do some good and still in spec. Output is 120W on 17M and 130 on 20M, Havent used it lower. If your running a dynamotor figure on 100W or a bit more with new tubes. Filament voltage is also critical.

OTOH a modified Globe 300A with an 813 does up to 175W out at 1200V and getting enough drive (15-20ma) is the secret plus running the max screen voltage of 350V.

You also need enough bias to keep it in deep Class C for best audio and that also means plenty of drive.

Carl

[KC2TAU]

Carl, I'm running off of a homebrew supply. I've brought the filament voltage up to 27.9 volts and that seems to have helped things a bit. My issue seems to be lack of plate current. I tried substituting in some 750pf 6kv rated ceramic discs for the air variable and it made things worse. I tried at both 750pf and paralleling for 1500pf and, besides losing the adjustment factor of the air variable, it made less power. I'm not running out of capacitance as when I use the air variable and control D for loading I find a point where there is a peak in power and it's not at the end of either control's travel.

I need some clarification, though, as I've read three different things regarding this. When control C, the coarse loading, is at position 7 and below control E is used to dip the plate and control D is used to load the final, correct? The reverse would then be true at position 8 and above on control C.

The transmitter performs its best when control C is at position 5 but what bothers me slightly is that I find the plate dip on control E at 200, right at the edge of minimum capacitance. I can advance control C to position 6 and then I will find the dip at about 180 on control E but power is less than when C is at 5.

With control C at 5 my plate current off resonance is slightly under 80ma and the current on resonance at 1300v HV is just a hair under 60ma with the antenna current reading slightly over 1.5 amps.

I'm not ruling out a soft 813. I'm just not used to the lack of jump in plate current when the final is tuned off resonance. I also want to cross check my watt readings with other meters to get as good of an estimate as I can.

Finally, with the transmitter unkeyed and in AM mode when I touch the tip of the 1/4" plug on the other end of the 1/4" to .206 conversion tail that I have leading into the microphone jack (the ART-13 takes its audio in through the ring of the .206 plug) I hear a 60hz hum emanating from inside the transmitter. The plate current meter jumps upwards as well. Remember, this is with the transmitter unkeyed.

[N8ETQ]

  I had a wattmeter like that once.  Glad u got er goin Mike.

/Dan

It's significant to me as it's quite a bit lower than what others have reported seeing. In addition the previous owner sent me a photo of the transmitter loaded to 160W on 75M. I'm taking that with a few grains of salt but even so...

I'm going to run it into a dummy load and see if the problem is with the antenna. I'll verify the LV as well.

[KC2TAU]

I've been working away on the ART-13 and I've made a bit of progress. As I had mentioned the first thing I checked was the filament voltage and that was somewhere around 24 volts and so I used a variac to bring that up to nearly 28 volts. In addition I checked the 400V supply. Unloaded it was around 385v but it dropped to 366v when the transmitter was keyed. The line voltage in our area is somewhat low as it tends to hover around 119-120v and putting a 7 amp load on a 15 amp circuit brings the line voltage down to around 115v. Considering this I'm using a 15 amp variac to bring the voltage input for both the 28v, LV and HV power supply back up to about 125v. With the power supplies operating at a more appropriate input voltage the LV voltage under load is now much better at 400v. Power output is now up to about 125 watts with about 1350v HV under load.

I had the transmitter on the air a few days ago and talked to quite a few nice folks including Todd, KA1KAQ. At this point the supplies were still running below voltage but even so I just about managed 90% positive on the scope. I'm going to sift through the tubes and make sure they're all strong and perhaps now with the improved voltages 100% positive will be in reach. I'm currently using a very simple set up consisting of a Shure SM58 into a Behringer 802.

I'll post some pictures shortly. We're getting there!

[KC4VWU]

Glad to hear you got the problem resolved and the tx is up and running. I still haven't had the time to dig mine out yet.

73, Phil