Ok...So I have plenty of 15E tubes and 1625's, and I'd like to use these to build a transmitter because it's what has fallen into my lap and I figure I should try to use what I have. I've got supply for 1500v and 750v. At 1500V 2x15E should be about 150 watts
http://www.nj7p.org/cgi-bin/tube?tube=15e . And the 4x1625 in ab1 will do around 140W. I could run 1625's in the rf section but I guess I want to be difficult and use the 15E's. I'm thinking 2x15E's at 1500V class c parallel modulated by 4x1625's AB1 push pull parallel. I gathered some info from this forum and been doing some reading to try to understand this better
http://amfone.net/Amforum/index.php?topic=27244.msg207633;topicseen#msg207633 So I want to be able to modulate the rf tubes to 100% so I take the plate voltage 1500*1.1=1650V So if I had a voice that was asymmetrical my peak would be 3150V and -150 for the negative peak BUT of course that is impossible, it would be over modulated.
The 1625 tubes will only go to 150v at 0 bias due to physics correct? So 750-150=600 then 750+600=1350v 1350-150=1200 (1200v) peak across audio tubes on the modulator side. So the peak for the rf deck 1650/1200=1.37:1 for voltage ratio which is also turns ratio. 15E in class c at 1500v operating conditions is 67ma. So impedance is 1500/(2*67ma)=11,194ohms, works out to be around 6000 to the 1625 tubes which is the "perfect" load for the 4x1625's right? according to this artical they say impedance is 6k
http://www.arizona-am.net/PHOENIX/NA7RH/ARRL%201625%20Mod.pdfI could have also takin 11,194/6000 then took the square root of that and ended up with a very similar turns ratio.
Now I could go to a higher impedance on the tubes and would gain less distortion, but would loose efficiency with tube power output. However I should have enough head room that I could go a little outside but I don't know how far? Would 1.2:1 provide to much impedance on the modulator? I'm not even sure what common modulation transformers I can find(haven't looked yet)
Now here is another question I have for myself. I have 2x20H chokes that I was planning on using at least one for a modified heising modulation settup. Problem is from why I understand the rf amp impedance plays the role in what size inductor is required. Makes since to me because the lower the impedance of the rf amp the less the rf "sees" the inductors impedance. So for 11kohm for the 15e that is way to much. However if I went with my original plan and used 4x1625 tubes in the rf amp I could use just one choke and it would work fine correct? Because the formula I saw was 10H for every 1K of impedance. I really wanted to use this set up. I guess it depends on what mod transformer I get rather it is worth even doing this. Maybe at the power levels I'm talking about doing it is pointless? Would it make finding a suitable transformer much easier to just use 4x1625's modulated by 4x1625's?
Thanks for your help. I hope I've got at least some kind of idea what's going on here.
