Amount of exciter drive for CSI T-20-F1

[brandonb959]

We have a CSI T-20-F1 that was upgraded to a "25KW" plate transformer back before my time as engineer (I was told it once ran at 25KW at another site). It has been running at a TPO of 12KW for the past ten years but we are looking at a new antenna that will require around >20KW of TPO. Currently @12KW it takes about 10-12 watts of drive from the exciter (the IPA is an internal 5cx1500).

Over the past month or two the transmitter has gone down 2-3 times with the plate breaker thrown each time. I finally lifted the tube out to find that the grid collet was arcing to the tube and the fingers were "charring" off. I replaced that along with a "seized up" tuning bar and gave the cavity a good cleaning tonight.

After getting it back up and running I tried running the exciter drive up to see if I could get to 25KW but it leveled out around 16KW at around 20 watts of exciter drive (Yes I did properly calibrate all tuning and loading parameters as I went). I realize that either of my tubes may not be at 100% but my question is to whether I will need a 3CX20000 rather than the current 3CX15000 in order to get to 25KW? And will a 3CX20000 fit in my socket? I can't seem to find any test data in my manual to show what the drive should be even at 20KW. I know that was a mouthful, any thoughts?

[Dale H. Cook]

It sounds like you are not getting enough drive from the IPA. Do you have test data for 20kW output showing what the PA grid current should be?

The 3CX15000 should make 20kW with no problems. IIRC that was the final that I had in a ca. 1972 CCA 20 many years ago. It also had, IIRC, a 5CX1500 IPA and the condition of that tube was critical to getting full TPO. I was driving the CCA with an MX-15 so your CSI should not require an unusual amount of drive.

[Deep Thought]

Yeah, if that 5CX1500 is not in prime condition you'll never make power. In fact, there are few CSIs which made namplate power even when new...

[brandonb959]

The tubes are my number one suspects as well, everything else seems to be correct. I informed the powers that be that we will probably need both tubes replaced for the new TPO.