I could tell I was beating a dead horse when all the HFers ignored my earlier comments about plate bypass capacitors made of two metal plates with an insulating sheet between, and then when they kept talking about pi-nets while purporting to discuss V/UHF amplifiers. Some folks seem enamored by the view of lumped constants arranged and connected willy-nilly. But Hank, W6GGV, raised me knee-high on stripline design, and I've never forgotten the difference, nor how easy they are to design (not necessarily to build, however!). They'll just have to learn the hard way, I spose, just like I'm having to learn how to make holes in this desert cliche for tower bases.

I can just imagine one of these characters looking upon a typical V/UHF amplifier tank circuit and wondering "just HOW the hell can this thing possibly work?!?! How do you calculate the inductor in the output tank, fer Gawd's sake???"? 8-)

Steve, K0XP

?

Guess what the #1 component that fails in FM broadcast is ?? ?It's always the teflon plate block assy.? ?I just saw one, this time made from polyimide? cut loose 6 months ago, ruptured, blew up.?

?

Years ago, I tried a hb plate blocker by 1st wrapping the entire circumference of the anode with teflon sheeting....then a wrap of wide copper strap ( narrower than the teflon sheet).? ?Problem is.... the total C is formed by the entire circumference,
but the rf current exits the blocker at only one point.... so it's all concentrated at one point of the circumference.? ?You can also get imperfections (air pockets) between the anode and teflon...and also between teflon and copper strap.? That's when the corona starts up..... and you can't see it.? I experimented with it, using a YC-243 tube, with it's 6.125" OD anode cooler / 19.24" circumference? ( socketless 3x6)? for 2 months...then gave up, went back to a conventional assy, using paralleled? HT-57's.?

?

In the older arrl books, and also orr books, they both depict 8877 being used on 144 mhz...and also 220 mhz..... and both used a T network for the tuned input.?

?

Years ago? I had buddy try a T network? ( series coil, shunt C, series coil)? ?on his 2 x GS35B? 6m amp.? ?After a week, gave up, went to a pi net, with small air caps and one coil.... end of problem.?

If a simple T / PI network will work as a tuned input......mounted right at the cathode.....and is fully adjustable, what is the advantage of a strip line config ???

?

My issue with any tuned input is...... change anything, like drive level, bias, B+, length of coax to xcvr (or ipa), etc, and it always has to be re-tweaked a bit.? That's why a fixed tuned input was not used on the 3x6? 6m amp.? Besides, we needed something? we can slam 500-700 watts? CCS? drive level......on data modes.?

?

On these multiband? GG triodes,? I was not about to construct 5-9 separate PI tuned inputs...all bandswitched.? 2 x broadcast caps ( padded on 160m) and a simple 4 uh tapped tubing coil works superb.? We tested it on every band by stuffing a 800 w cxr though it on each band for 10 mins...then into the 2nd bird meter, then the 50 ohm DL.? ?6:1 verniers on both caps..then the 0-100 scale.? Then it's just...'tune by the numbers'.?

?

On my next amp, I'm going to 1st experiment with a new 0 - 4.4? uh roller coil ( multronics / cardwell...now called Viking).? It's wound with 8 ga wire. Then I can experiment with changing the Q on any band..... the idea is to see the effects of IMD? vs tuned input Q, and other parameters.?

?

Jim? VE7RF