The AM Forum

THE AM BULLETIN BOARD => Military Amateur Radio Section => Topic started by: KD2AZI on December 20, 2019, 01:54:40 PM



Title: ART-13 operational!
Post by: KD2AZI on December 20, 2019, 01:54:40 PM
So after six months of work my ART-13 is finally hooked up and putting out some power.  I tried to get into the AM Carrier net last Sunday and had some glitches.

I'm new to AM so have some questions, and appreciate any suggestions!
My BC-312 receiver's muting relay was not working so I replaced with a P&B unit, grounding the antenna and first audio grid when the transmitter is keyed.  However, I'm still getting a horrible squeal/feedback when transmitting.  I tried removing the receiver antenna line from the ART-13 relay to no improvement.  In fact completely disconnecting the receiver's antenna has the same results.  Even grounded I still get the feedback.  The only thing I didn't try is moving the receiver a few feet from the transmitter.  Any ideas?

I'm putting out 80 watts, and is that enough for "regional" 40m contacts? - the net had trouble making out my transmission.  I don't have a high-gain antenna, and wondering if all you gents use big amps?  (I have a Viking T-bolt and an HK Warrior perhaps I could try)

My plate/screen voltages are 1100/425 w/no sag
Modulation looks good on the scope w/carbon mic
Radio's PTO has little drift, and using digital frequency counter.
Antenna is tuned to around 3885 (Gap Titan DX) - no other choice in antennas.


Title: Re: ART-13 operational!
Post by: W6TOM on December 20, 2019, 03:45:23 PM
   For AM you really need the most power you can get and best antenna. My ART-13 which I run off the dynamotor gives me around a 130 watts of carrier on 75 meters, I use a D-104 microphone. The carbon mic did not modulate well or get good audio reports.

   These sets were made to load into a trailing wire antenna and not a 50 ohm load, I think 80 watts of carrier is a bit on the low side.

    Henry, WA7YBS, has a lot of good info on his site about the ART-13 including using an off board capacitor to improve loading.

    https://www.radioblvd.com/art13.htm



Title: Re: ART-13 operational!
Post by: N8ETQ on December 20, 2019, 05:49:05 PM
  

  yo'

          U may want to try padding in a 500 pf cap.  Hook it to the
"LOADING" connection on the side panel and chassis.  One of those
"Big Un's" with screw connections.   The power will come up.
Disconnect the cap when on 40 or higher.

GL

/Dan
N8ETQ  CLE





Title: Re: ART-13 operational!
Post by: KD2AZI on December 20, 2019, 09:39:08 PM
Thanks guys - I have been all over that Radio Boulevard site, and I do have a 1000 pf variable hooked up to the COND Terminal. at 3885, the best loading is with minimum capacitance.  I have a bunch of spare 813s, I'll try a few others and see if output improves.

Also, I think I may be over-modulating; the pattern has some flat lines in between.  I did that mod in the audio unit to change R203 from 15 to 4.7k for the carbon mic.  I'll take another look at this.


Title: Re: ART-13 operational!
Post by: SM6OID on December 22, 2019, 05:16:57 AM
Hi!

Another ART-13 on the air, that is good news!
I have two ART-13 in service, one with LF oscillator.
With increased bias the T-17 carbon microphone works fine, but an ElectroVoice 638 with W2IHY EQ makes great audio.
Currently I see a hair shy of 130 W (3.7 MHz) on a good day with dynamotor, supply voltage is a bit low, 26.8 V at load.



Title: Re: ART-13 operational!
Post by: KD2AZI on December 22, 2019, 12:02:29 PM
Yes, it is good news.  Having fun with it.  I did the mod to replace the a resistor in the audio section to a lower value for the carbon mic bias - I'm over modulating now, and need to revisit that.

I have a bunch of 813s I've been hoarding and I'll try boosting the B+ a bit and trying some different tubes to see if I can increase the wattage a bit. 
The antenna is tuned to 1.31 SWR @ 3885 and I think that's the best I'll be able to do with my small space. 
Will try again next week after working out some glitches.

By the way, even with receiver muting it's overloading on Xmit which is actually making it easy to spot!
73

(https://live.staticflickr.com/65535/49221727548_810fe88e59_b.jpg)


Title: Re: ART-13 operational!
Post by: SM6OID on December 23, 2019, 10:40:40 AM
Hi!

You know what, before you do anything about the mic bias resistor, have a look at the power output "issue".
First, play around with alternative setting of E-C-D knobs, it is possible that you will find a settings combination that will give you more power! If this is a dead end, swap PA tube and see what happens?
How much indicated GRID DRIVE do you see?



Title: Re: ART-13 operational!
Post by: W6TOM on December 23, 2019, 04:41:41 PM
  I have two of these transmitters, one is an early ATC and the other an ART-13, I had a problem at different timers with both in that the modulation would go away. I decided to try replacing all the electrolytic capacitors in the speech amp, that solved this issue.


Title: Re: ART-13 operational!
Post by: KD2AZI on December 26, 2019, 02:39:23 PM
Yeah, I replaced those capacitors too...on another site the pros identified those as paper in PCB oil...and those electrolytics in the audio module took some time to replace.

I'm now getting about 120 watts out on 80 meters, and working out the glitches slowly - with some mods to the receiver muting the feedback is gone.
I'll hopefully be ready for another QSO attempt in early Jan!


Title: Re: ART-13 operational!
Post by: SM6OID on December 27, 2019, 03:17:01 AM
Hi!

Nice of you to share the good news!

What was the reason for the "low power condition"?
Poor tuning strategy or a tired 813? Or what?

Please let share your experience, so we all can learn!


Title: Re: ART-13 operational!
Post by: KD2AZI on December 27, 2019, 09:25:03 AM
The low power condition was addressed by increasing B+ to 1150v, and trying different 813s. I've been hoarding them from hamfests.  (odd that I never noticed that 813s have a couple different plate makeups, btw).  Grid drive is just left of center.  I have not experimented with adjusting the screen supply - it's about 420v

Tuning was easy to figure out, and the frequency counter helps keep me from tuning in a harmonic - which I discovered when trying to tune up on 40m.

Tune-up is a bit tricky when control E is close to "200;" you've got to be careful not to switch between scales while tuning up - the manual warns about this - and it's happened once...or twice if I'm honest :|

I have found the PTO in this rig to be stable, and at some point I'll collect some data.

The power supply was a significant build for me and it took a long time - felt like an apprentice with a master largely on vacation.  The effort paid off - I've had no issues with it.  For PS design I started with the article on RadioBlvd, then found an article on the 'net by Antonio Vernucci, I0JX; both of these have the interconnection leg-work done (for those w/o the dynamotor) and it simplified things.  The unit started off as a Bendix military radar test set and the case, panel and chassis are beefy so I was able to fit in two swinging chokes and transformers as well as the 27v switching PS and variac without bending the chassis.  I filled the panel holes in with JB weld.  The discrete components and relays are under the chassis.  I used all second-hand parts except for diodes, caps and balancing resistors.  (I did splurge on new wire from Remington Industries).  Got the idea for the Meanwell switcher from the Radio Blvd site; it works great, is adjustable, and handles the load surge fine.  So far I haven't noticed any noise from it.  Also small form factor, and $35 online.

One tip I got was to buy a stepped drill bit to drill through the aluminum panel - that thing is a dream, plus the pile of hole bunches I bought from a SK estate.  I also learned a lot about drill bits, and proper drilling technique.

This site helped me with the T17 mic: http://k4che.com/T-17/T-17.htm (http://k4che.com/T-17/T-17.htm)
My favorite part is the IBM dictaphone footswitch I use to switch the Ant/Dummy Load relay.  That thing is built like a tank.


Title: Re: ART-13 operational!
Post by: Opcom on December 28, 2019, 02:11:11 PM


Yes, it is good news.  Having fun with it.  I did the mod to replace the a resistor in the audio section to a lower value for the carbon mic bias - I'm over modulating now, and need to revisit that.

I have a bunch of 813s I've been hoarding and I'll try boosting the B+ a bit and trying some different tubes to see if I can increase the wattage a bit. 
The antenna is tuned to 1.31 SWR @ 3885 and I think that's the best I'll be able to do with my small space. 
Will try again next week after working out some glitches.

By the way, even with receiver muting it's overloading on Xmit which is actually making it easy to spot!
73

(https://live.staticflickr.com/65535/49221727548_810fe88e59_b.jpg)



What model of scope is that on the left? I think I have the 3" version, very nice mod scope.


Title: Re: ART-13 operational!
Post by: KD2AZI on December 28, 2019, 08:42:44 PM
That's the P&H RF Distortion Indicator model DI-1.  I recapped this, and changed the HV selenium rectifier, and a couple of resistors.  Works fine, I just wish it had a sweep control!


Title: Re: ART-13 operational!
Post by: Opcom on December 28, 2019, 10:03:46 PM
That's the P&H RF Distortion Indicator model DI-1.  I recapped this, and changed the HV selenium rectifier, and a couple of resistors.  Works fine, I just wish it had a sweep control!

Oh, I see, I thought it was a Multiphase. Similar logo and good looking!


Title: Re: ART-13 operational!
Post by: KD2AZI on December 29, 2019, 08:10:40 AM
Yep, the CE Multiphase has a sweep control, and one will be on the bench soon.


Title: Re: ART-13 operational!
Post by: KD2AZI on April 26, 2020, 07:31:32 PM
So after some work I'm now getting 160 watts or so output.
I tried a bunch of different 813's until I found a strong one, then replaced my PS transformer as the screen voltage was a tad low.  I also took the plunge and realigned those delicate ceramic capacitors to maximize the grid drive.
I've set three channels up for 20, 40, 75m calling frequencies.

Now alls I need is a QSO!


Title: Re: ART-13 operational!
Post by: KA3EKH on April 27, 2020, 02:37:39 PM
Think you are over in NJ just up the coast from me. 3885 can be a bit stuffy with all the people who live on that channel but you may want to try the Old Military Radio Net on Saturday mornings. That will give you the option to talk to several other ART-13 at that time. Also think about 7.296 and the MMRCG net at ten EST on Saturdays. The first of the month everyone runs AM but the rest of the month they run USB, I will be on Saturday probably running my ARC-38
Anytime you want to operate on 7.290, 7.160 or around any of those places let me know and I will fire up one of the radios around here. Would also like to try 14.236 or what ever the AM calling frequency is for 20 being have never done a contact up there.
Maybe we can also get you a BC-348 to go with that transmitter and you can have the complete ARC-8 set up, then all you need is a WW2 bomber to put it in.




Title: Re: ART-13 operational!
Post by: SM6OID on April 28, 2020, 06:36:18 AM
Hi!

Nice to hear about progress!
With 160 W worth of carrier, you still get 100% modulation?

I still run my two ART-13 from the dynamotor, wish I had a second dynamotor, now I have mess around with cables to switch transmitter. I have not done any adjustment of the delicate capacitors, I have good grid drive and I see about 100 W on 20 meters.

Have had a number of QSO with the US on 20 meters CW and a BC-348-Q (with dynamotor).
AM QSO's are limited to, usually, Sweden and Norway.
I guess I'm one of the very few, over here, that work AM on 80 m here on an almost daily basis.


Title: Re: ART-13 operational!
Post by: KD2AZI on April 28, 2020, 09:27:58 AM
Quote
I have not done any adjustment of the delicate capacitors

This was not hard, I sprayed a bit of electrical contact cleaner on them, and was very careful in breaking them free.  Replacement looks like it would be surgery!

Quote
let me know and I will fire up one of the radios around here.
Thank you, I'll reach out!


Title: Re: ART-13 operational!
Post by: W2JBL on May 24, 2020, 07:57:46 PM
   Congrats on getting a nice looking ART-13 on the air. Great rig. I'm one of those "stuffy" ops from 3885. I run an ART-13 there frequently. All are welcome on 3885. Now the "stuffy" part: There are a lot ART-13's on the air. Guys use the amplified D-104 with good reports on them. Keep the T-17 for the miltary net. I have one too and it usually lasts one transmission on 3885 before somebody protests! Also: AM on 7.160 was common 10 or more years ago. Today it's in the SSB DX window. Please refrain from using AM there. Same for 14.236. It's the SSTV window. Those guys REALLY scream when you get on there, even on SSB.

73
DE W2JBL
 
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands