The AM Forum

I'm slowly working towards getting my ART-13 on the air. Everything is working fine except for the filament for the two 1625 multipliers. I'm not sure what the issue might be. I measured pin 1 and 7 on V102 which should be first in line for filament voltage. I need confirmation on which pin is which. On V102, if one is looking at the socket from the control side of the transmitter, I measured 22vdc on the right filament pin (the two larger pins) and 0vdc on the left pin. On V103 I'm measuring 0vdc on both pins. Both 1625's test just fine and have good filaments. I'm a bit confused as to what the problem might be. The battery voltage meter is indicating voltage and every other tube filament is operating properly. Any ideas?

It sounds like you have a ground between the 2 tubes.

Carl

Hi Mike,
             Make sure the 813's are seated good into their sockets. If I remember correctly, I had the same issue about 2 years ago. It will look like it's seated correctly, but since the socket and hole alignment is so tight, the locating pin on the side of the tube will hit the chassis and prevent it from being inserted all the way. Lotsa jiggling, twiddling, and cursing at this point, but I managed to get said tube seated after removing the rear sheet metal to see what was going on. If you do that, you can also get to the relays pretty easy and clean them while you're there.
             
73, Phil

Sorry, too early in the morning (afternoon)! Now I see he said the 1625's

Been there on that one too. I believe about the same issue; dirty socket contacts or bad solder joint. Have you switched the 1625's around and checked ?

---Phil

The 813 filament lights up fine. I'm getting continuity between opposite pins on each tube (i.e pin 1 of one tube is continuous with pin 7 of the other). That seems okay. A ground may be an issue. Has anyone poked around that area? Is the wire connecting the two filaments on each tube in a particularly tight place?

The 1625s are 12..6 volt tubes and the ART-13 runs on 28VDC.

So those two 1625s are in series -- hence you will get zero volts on two pins where the 1625s filaments are connected together -- as well as on the pin that's grounded.

Also, the ART-13 has a complicated system of series and parallel tubes and series resistors to get all the 6.3, 10, 12.6 etc. filaments working off that 28VDC supply.

Most likely cause of your problem is a bad connection (or broken wire) at one of the filament pins on one of the 1625 sockets.

Note that if one 1625 doesn't light, the other won't either because of the series connection.

IIRC the 813 is in series with the 811 filaments (2 x 6.3v + 10V) with a dropping resistor and a parallel resistor to make up for the different currents and voltages.

In fact, you can seen these wire wound resistors next to the 813.

That's a separate circuit from the 1625s filaments.

Yes, I believe the rear tube is the second in the string (V103), and one contact should show ground to chassis. the other should show continuity to one contact on the other (V102 - front) socket; the other contact - full fil. string voltage. Make sure the contacts in the socket are tight. Go in and carefully re-tension the contact fingers for the fil. pins on both sockets.

---Phil 

Very good. I'll take a look at things when I return in a few days from vacation. Are there any tricks in accessing the tube sockets for the 1625's from the bottom of the transmitter?

I'd try wiggling the tubes first and see if you can make the filament light.

If so, you would know you were on the right track.

Then, try cleaning the tube pins first as that's easy.

Then, perhaps try a little contack cleaner thru the holes on the sockets.

If all that doesn't work, then you have to take it apart and that is a PITA.

It's a PITA! Do not remove any of the autotune stuff for access because I understand that it is also a pain to deal with; as in removing the osc. module to gain access.

Let me pull mine out and take another look. It's been stowed away for well over a year since my move and I haven't had time to play with it any. As a matter of fact, I have 3; the working unit being the worst of the bunch, purchased as a ratty parts rig.

You get that rig rolling, Mike, and I guarantee you'll love it! Not a powerhouse by any means, but coolness factor is at least a 10.

---Phil 

As has been mentioned, the 12 volt heaters of the two 1625s are in series.
Pin 7 of V102 should have 24 volts on it. Pin 1 of V102 connects to pin 7 of V103, and both should 12 volts present. Pin 1 of V103 is grounded.

So why is there 24 volts on pin 7 of V102 and 0 volts on pin 1? A short to ground on pin 1? (or a short to ground at pin 7 of V103?) That would put 24 volts on V102 and its heater would be way brighter than it should be. You don't really need to read voltages from underneath to determine what the problem is. Look at how bright V102 lights up. If it's way bright, then there's probably a short as I mentioned which you can check with an ohmmeter at pin 1 of V102. You can also wrap a fine wire around the pins of each tube to read voltages from the topside.

Bill

Bill, neither 1625 lights up. Both tubes test good. What bothers me is that both 1625's slide into the socket too easily. I tried wiggling both while DC was applied but nothing happened. You're right, I have 24 volts at pin 7 and the battery voltage meter is operational so I should at least see V102 light up. I'll perform some ohm readings as well. I'm hoping it's just that the sockets are too loose to obtain firm contact of the filament pins.

Phil, can the fingers for the pins be adjusted from the top side? If I remember correctly I was finding that pin 1 of V103 was grounded to chassis so that's good. I'm not going to remove the auto tune, don't worry! The auto tune works great and so I want to leave that alone! I love the rig already. I've put a fair bit of time revising the power supplies that were supplied with it and so this is just part of the adventure.

Hi Mike,
            I managed to get to them from the top, but it's not easy. You'll probably need an assortment of small picks bent in different angles. Harbor Freight and a lot of the auto parts stores sells them. It would probably be best to remove the audio amp, MCW unit, and the sheet metal facia from that end for access as well. Just go easy on them.
             The heater pins may be so loose that one may not be making connection at all. Bill just gave a good idea; wrap some small gauge wire around the pins near the base to make the test measurements. That way, you'll know the pin to contact fit is good underneath the test connection. 

73, Phil

Phil,

Any tricks you used in getting a grasp on them? They look to be down a ways and set into the pin. How did you manage to pull them out? I have a variety of small tools at hand. I'm curious as to how does removing the audio amp, MCW unit and sheet metal fascia help?

Well, for me it made it a little easier to get down to the sockets and gave more flexibility in maneuvering the tools around at different angles. Harbor Freight has a small pick set (4 pcs.) that works well. Just don't go overboard; all it needs is a little tweak to re-tension the contacts.

---Phil

Oh! Those pictures help make things much more clear. I'll definitely need a proper pick set then now that I see how the pins are arranged. Thank you for the pictures!

They will slightly rotate side to side also, since there is a single rivet holding the contact to the base. Some may have two. Eventually though, you know what will have to be done: this is really just a bandaid repair. Get it rolling and maybe you can catch the OMRN in the morning on 3885 kc.

73, Phil   

   I can't recall the details but is that filler panel installed.
I thought there was an "R" on that to complete the fil
string when not using the LF VFO.

Just a thought.

/Dan

Hello Dan,

This one has the LFO installed and its 1625 is getting filament.

Phil,

Your tips are invaluable. Thank you.

Well, it turns out the tube socket issue was a case of operator error. I went searching to see if I could tighten the sockets and so I started to remove the bottom back panel in order to see what access was like it. While taking out one of the screws I heard the "plink" of a nut falling off behind the panel. Great, so now I absolutely had to take the panel off. I ended up turning the transmitter over onto its back and removing the bottom panel so that I could access a small steel tab that was connected to one of the relays. Space was extremely tight to reinstall the nut but what I did was use a pair of needle nose pliers in my right hand to hold the nut. I then had a small eyeglass screwdriver in my left hand that I used to gently push the screw up against the tab. I used such a small screwdriver so as not to put so much pressure of the screw that it would push the tab away and prevent the screw from threading through the tab. I then put the needle nose pliers down and behind the tab and searched around for where the leading end of the screw was. I knew I was about there when I saw the screw head just push out a bit. I started tightening with the screwdriver and was very lucky to get it on the first try.

With that sorted I looked inside to see if I could locate the tube sockets for the 1625's. They are quite hidden under the capacitors for the multiplier section. Fortunately the pins I needed to tighten were actually in view. After trying a bit to tighten them with the pick set I wanted to see if this had made any difference. So, balancing the transmitter on my knee to keep it at the correct angle and inserting the 1625 into the socket with my left hand I noticed something funny. When I thought the tube was in its socket I realized that the pins weren't even seated into the socket yet! Pushing a bit harder seated the tube firmly into the socket! I hadn't been pushing hard enough! After I reassembled everything and put it back together I was pleased to see filament light from the 1625's.

Everything seems to be working quite well except for the fact that the output power is low. With about 1300v on the plates I seem to be getting about 90W at best. Battery voltage is within specification, grid drive is good with the needle moving to the middle of the shaded white area and the antenna is resonant. I don't seem to be getting enough plate current. At the moment I'm seeing a little over 60ma of plate current. I can't seem to get it to go any higher. I would expect that through proper loading I would be able to increase the plate current to where it needs to be but I can increase only up to 60ma. When I tune the final off resonance the plate current doesn't spike much more than 20ma. Also, is it normal to not find a plate current dip when the loading is set lightly? When coarse loading control C is set to 1 or 2 and antenna tuning control D is set at 0 I am unable to find a dip. When control C is set to 4 or 5 I start to see a dip.

I'm using the transmitter with an external air variable loading cap provided by the previous owner. It looks to be three sections at roughly 365pf though I'll see if I can verify that this evening. This should give me enough capacitance on 75m. I'm finding that maximum output occurs with it 1/2 meshed. I've tried taking my tuner (Heathkit SA-2040) out of line with the transmitter but that does not help matters. I know that the ART-13 should be capable of at least 125W, if not more.

The modulation looks good on the scope. I need to make a 1/4" to .206 adapter so that I can run my mixer controller SM-58 through it so that I can shape the audio at least to some degree. The D-104 I have with it sounds, well, not how I'd care for it to sound. The modulation looks clean, though, and that is what matters.

  Damn !

     I have found the ART-13 power output is more sensitive to changes
with the LV rather than HV. but if it looks good on the scope 90 to
125 w is insignifegant.  More drive plus higher screen "E" on the 813
will make it perk up a bit.

Glad you got er' done.

/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.

 Yeah, they can keep up with a Valiant, I have 2 of em here. One makes
about 75 W and the other about 90.  You can try 500pf exra "C" on 75.
Hook it between that "Load Coil" terminal and the bottom plate. It helps
a bit.

GL

/Dan

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

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.

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

/Dan

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

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.

Pete,

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

73DG

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

Sorry Mike, good drugs here I guess.

73DG

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

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.

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

/Dan

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!

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