[Amps] Stripline design

[Paul Decker]

Hi group,

I have a homebrew 70 cm stripline amplifier built around the 3cx400A7 tube.  As everyone know's, it's getting rare and expensive.  I was thinking that it would be really easy to change over to a 3cx800A7 or 3cpx800A7 tube since it uses the same socket (I have a few sitting around), and comparing the datasheets, they are electrically very close.  Besides the obvious like size and heater voltage, there are slight differences  in cin and ck, but I'm not sure how that will effect it.

Because the tube anode cooler is physically bigger, I would have to make a new stripline with an extra 3/8 inch  on the end.  My question is two fold.  1. How does one calculate the actual length of the stripline in the first place, and 2, more of immediate concern is would that extra 3/8" make any difference?  My "gut" feeling is it won't, but I have no basis for that.  Here is a picture of the stripline out of the rfdeck:
http://a4.sphotos.ak.fbcdn.net/hphotos-ak-ash4/388232_2684319340428_1029693354_32301613_317232212_n.jpg

My current stripline is 8.625" and I would extend it to be 9.0".  I looked at K1FO's single 3cx800A7 design and his stripline is 9.6875 and the same width of 3.5".  I also looked at his 2x3cx800A7 design and that stripline is 9.0", the same as mine would be.

Here is a picture of the whole amplifier project:
http://a5.sphotos.ak.fbcdn.net/hphotos-ak-ash4/247265_1908478664896_1029693354_31782436_481699_n.jpg

Just to head anyone off at the pass.  I am doing this for two main goals.  1.  So that I have a replacement tube, and 2. more power and more headroom for JT65. (I way more voltage and current than the 3cx400 could ever want, plenty to supply two 3cxp800's).  I thought this would be an easy stepping stone for now.

Thanks and 73,
Paul, kg7hf.