Power Drop-off on the ART-13 on higher frequencies

[KF9CM]

I completely cleaned and aligned My newest ART-13 (the third one I have) and I have a drop-off in power as I go up to each band. Into a Bird 43 I'm getting 165 watts on 75 meters as well as 160 meters, but when I go up to 40 meters I get 75 watts. Then on 20 meters it's 20 watts and on 17 meters it's none existent.

I've done a complete alignment as per the Tech manual and I'm beginning to wonder if I've got some bad caps.  Particularly C112 250pf plate to grid coupler between the 1st and 2nd multiplier. I know someone going to say change it, but if you have ever taken apart the ART-13's multiplier and VFO sections, it's kind of like taking apart a pocket watch. If any one has had a similar experience with the ART I would appreciate any help.

TNX Gary

[W2JBL]

my ART-13 puts out 200-250 watts on 160 through 40 with 1550V on the plates. on 30,20,and 17 anything more than 150-175 is a gift from the gods. you need to see lots of 813 grid curent on all bands, and it drops off above 40. on mine the screen resistors in the 1st and 2nd multipliers were nearly open, and the screen bypass on the 2nd multiplier was very leaky. after fixing that no alignment was needed and i got the good power out numbers. watch out on 20 and 17 by the way- the PA gets squirlley up there.

[KF9CM]

Thanks for the insight.  I think I'll make some 1625 tube extenders and see which one is ailing. Then on to field stripping the old girl. It's so tight in there, maybe old man Collins never figured on any one working on the multiplier.

[WU2D]

How is your grid drive on the 813? I get into the grid paint on all bands. The trimmer cap stacks are tricky to tune without getting zapped - be careful.

It makes sense to maximize grid current on the ham bands that you are interested in. It is also very possible to tune stages to wrong harmonics since the VFO is operating in the broadcast band!

Mike WU2D

[WA1GFZ]

Mike,
Have you ever run an 813 at 750 plate volts. Thinking of dumping one in my PDM Viking 2.
only need 100 watts out.

[WU2D]

Works fine - lasts long time!

With 750 VDC on the plate, my ART runs 160 mA when loaded up on 80M with good grid current. That is 120 Watts input power. Sounds like a big (cool) 6146 which it really is at this voltage.

In Class C this translates to 60 - 75 Watts out. What can you do with Class E under these conditions?

Mike WU2D

[WA1GFZ]

So Mike I would need a pair of them to get over 100 watts at that voltage. I wonder if the 6AQ5 has the right stuff. a pair might not fit in the V2. Or might have to redo the tank and power supply to jack the voltage higher.

I've never built an 813 rig

[m0ghq]

I get around 175w on 80m using the original dyno, I have not tried my ART-13 on the higher frequencies yet, What microphone are you guys using as I find most will not modulate the transmitter more than about 50%. 73 Max M0GHQ