[Amps] Modified W2GN VHF Amplifiers

[Byron Tatum]

Hello-
    To anyone interested I would like to describe an undertaking here involving an adaptation of the old K2RIW / W2GN design. As you well know W2GN published amplifier articles in Ham Radio Mag. for 50, 144 and 222 Mhz. amplifiers based on the K2RIW style construction. The bulk of the drilling layout dimensions were published in the 144 Mhz. article. {There are a couple of typo errors in those dimensions shown in that article}. However, there was never a 432 Mhz. article published by W2GN { just the original K2RIW article} although W2GN produced a 432 Mhz. amplifier {ARCOS}. Probably the only item of interest not provided by lack of W2GN article for 432 Mhz. is the plate line material and dimensions, as discussed in chapter in G3SEK " VHF, UHF DX HB". The plate line has slightly different dimensions for 4CX250 type tubes as compared to 8930 type. { 5" x 8-3/4" for 4CX250, 5-1/4" x 8-3/4" for 8930, both .062" copper or brass}.
    Anyway, what I am trying here is twofold : First: I have borrowed from the K1FO style construction { dual 3CX800} and developed a mechanical layout that results in the two amplifier chassis being enclosed in an aluminum cabinet with a front panel. I am using the standard 3" x 8" x 12" upper chassis but mating it to a 3" x 10" x 12" lower chassis. The lower chassis extends out the extra 2" and the front panel { 6-3/8" x 12-3/8"} is mounted to it. Side panels { 6-1/8" x 10"} are mounted to chassis sides that butt up against front panel and attach with small brackets. A top and bottom cover { each 10" x 12"} complete the enclosure. I have an enclosure together and it looks nice, will be a lot better finished out and painted, etc. I have a detail of drilling dimensions to mate chassis and attach panels to make enclosure. This style will work with 50 through 432 amps. It is done with .062" alum. sheet. Having the front panel mount to lower chassis front surface makes it a lot easier to attach front panel and build enclosure. I have a front panel layout detailing location of all control shafts, switches, meters.
    Second : I have adjusted the layout slightly { shifting tube socket centers 3/8" further away from chassis side wall} to allow for tube-end output flapper, as in K1FO type design. I have not heard of this being done in a K2RIW tetrode-type amplifier, perhaps someone else had tried it before? I believe it will work well, and I believe it is worth the effort of doing to allow for a more balanced current distribution around tube seals, plateline. I am going together with 144, 222 and 432 amplifiers now of this type design. I made a drilling template from a 8" x 12" aluminum plate that has 1/16" pilot holes that can be used to mate the two chassis together, drill all chassis holes { tube socket centers, get grid box mounted in exact location, input circuit component holes, etc.}, and mate top cover to upper chassis.
    Anyway, if anyone is still interested in the old K2RIW design this is my work going on with it. I don't want full legal power, plus I enjoy using the easier to find tetrodes, esp. the GS-36B { surplus version of 4CX400A}. I have used the GS-36B in other VHF amplifiers with great results, esp. at 432 Mhz. Plus, you can still use the old 4CX250 types for ecomomy. Actually, versions of the 7580W { 4CX250R} give a good account of themselves. A variant of 4CX250R sometimes seen in USAF surplus is the Y-400, a 4CX250R that is rated for 300 mA. class A cathode current, this guy is the best of 4CX250R series that I know of.
    Thanks all, WA5THJ.