The AM Forum

I have been noticing the modulation waveform on the ARt-13 has been looking kind of peaky of late.  Just swept it into a dummy load with my HP-201C, and based on what I am seeing below, I may be missing an 811 mod tube or at worst,  half of my mod transformer primary.  Tek 444 images below at nominal 1k, 3k, and 200 Hz, respectively. Resting carrier amplitude  trace adjusted to +/-1 major division on scope scale.  Looks like I am getting close to 100 on positive peaks, but have lost the negative side.  Really looks ratty at 200 Hz.  Fed the audio into the mic jack if the stock ART-13.  Hooefully I still have some 811s in tube inventory.

Can you put audio into the mod tranny and see what the transformr output looks like?  A quick? test for the tranny, if you don't have a known good set of 811s.

 ** NO  power applied **

KLC.

I will at least check DC continuity of the primary windings in the mod tranny.  Both 811 filaments are lit looking at the back of the set.  With max undistorted tone input that gets me to 100 % positive,  the HV current monkey is sitting right in the middle of MOD green band after loading to the middle of the CW green band in that mode.  Would be interested in seeing other ART-13 mod waveforms and where the HV current sits at 100% on tone input.

Do you have the Manual??

https://bama.edebris.com/manuals/military/an-art13/

klc

Now I do!  Tnx.  I first put mine on the air in the early 90s using the old Surplus Conversion
Manuals.  It’s just run and run, this is the first time in a long time I have had an issue to deal with in it.

I have (2) 13's....  I finally got around to making a proper power supply, with connectors and everything. I hated the JSed clip lead and 'lectrical tape supply I had. Time for something neater and much safer. I fired up the 'nice' one, blue flashes and smoke came out. Oh crap! So, naturally, I connected up the not so nice one, and smoke..... Crap!!  I had wired the connector backwards, the HV to the LV.  I was "yellofied!"   Blue  out the 837s and smoked a few parts. .... One of these days, I'll fix things right.

klc

I have been running my ART-13 transmitter since I got it and tubed it in 1992. I have only blown 1 modulation transformer so far. They can and do occasionally go bad. Should it turn out to be the XFMR, changing them out is not too much work. Good luck!

After Tron confirmed something I recalled about 572Bs being plug & play 811s on steroids, I pulled the pair of them from my SB-200 and put them in the ART-13.  Everything looks normal on the scope now, full clean positive and negative peaks!

The 572b will love you long time...... 

Some where there's a 73 Magazine piece about jacking up the power out on the '13. ..

klc

Yes, basically they're just 811As with graphite plates, I believe the filaments are the exact same rating on both, the grids are probably the same as well. The modulator for my homebrew rig was originally built with 811s, but it runs an unusually low voltage on them (just over 700 volts) and the primary on the mod iron is something like 5000 ohms, anyway it just didn't seem to run right with a pair of 811As in it, so I swapped in a pair of 572s and it seems to work better. My theory is that graphite plate in the 572B will handle the lower voltage/higher currents of a low-z load better than an 811 will in the same circuit, and be less stressed, since they have something like 160 watts of plate dissipation, an 811A is only 65, and a plain 811 is even less.

The Cin, Cout and Cg-p are all slightly different between t160l/572B and the 811, due to the spacing being larger in the 572b and its higher anode voltage rating.  It's within a few pf, so usually tuned out with the associated circuitry.

If you have to use 811As now, need new ones and don't want to go the 572b route, the ones from the Ryazan plant in Russia seem to be as good as rca or cetron, FYI.

--Shane
KD6VXI

For now may just leave the old 572Bs in the ART-13 and get some new matched ones for the SB-200 which I want to get back in operation with my Central Electronics 20A exciter For vintage slopbucket.

Then I take it you had a "flat tire" with one of your 811's.  You sound good now. I take it your resting current for the modulators - particularly the mod xfmr is OK. It shouldn't be too high for the xfmr.

Al