[Amps] AL-1200 back in business. Thanks!

[Kevin Normoyle]

  A big thumbs up!

I want to give everyone on the reflector a big thank you tonight..A 
bunch of people gave useful comments, some in direct email:
Carl KM1H
Bill W6WRT
Hal W5GHZ
Gerald K5GW
Alek VK6APK
Roger K8RI
Hsu ?
Ken KC6UFE
Ken N6KB
Jeff AC0C
Ron KA4INM
Billy AA4NU
Kermit AB1J
Hal W5GHZ
Kevin N9IWW
Hardy N7RT (Hardy is even selling my an older 3CX1200A7 tube for a 
spare. Thanks Hardy)
Monty WB5GLB
<hope I got everyone>


I got my 50W Zeners (1N3006B) and got them in tonite, and everything is 
hunky-dory! Full power back, plate current looks good in CW and SSB 
settings with no rf input etc. (well to be honest just checked full 
power 80m so far..will check out other bands tomorrow)

Interestingly, the holes in the Al-1200 wall were already big enough for 
the 50W DO-5 stud package (instead of the 10W package)

This makes me wonder if they were 50W at some time in the design, 
because the hole is too big for the smaller DO-3 package..i.e. not 
enough contact area between diode/mica/aluminum sandwich for optimal 
heat transfer (the hole is bigger than the insulating sleeve they used, 
needs...so it slopped around.

With the new 50W diode, I got a little insulating sleeve, plus the mica 
washer, which was nice and big in diameter.
I had to nick the sleeve like a split washer to tease it into the 
existing hole, but that worked great.

I made some insulating washers for the other side (nut side) from some 
FR4 laying around.

My biggest problem was that I somehow got it in my head that the "B" 
suffix meant reversed, compared to "A"..but "B" means +/- 5%  instead of 
+/- 10%. So I thought I was smart hooking them up backwards relative to 
the schematic, but then had to undo that and hook them up the right way.

The 50W diodes fit nicely, and I think that it's a good upgrade.

I also ordered a simple card from Ameritron (GOP-100) that supposedly 
will give me some grid overload protection?
I know there are other/better circuits, but thought that would be a 
simple thing that should give me some protection. Haven't got that yet.

I remember I first found posted on this reflector in 2005 when I really 
blew up a FL2100B. Had to repair lots of pieces on that, but got it back 
together with useful advice from here. (well to be honest, I need to fix 
the input swr on that, but am going to give that thing another look now 
with some new silver mica caps for the input tank).

At the time I thought "hmm. this might be the most dangerous forum on 
the internet..and I'm not talking high voltages..." :)

I did sand off some residue from arcing on the brass tab on the plate 
capacitor as suggested, also.

oh, another thing that confused me, because I had never measured the 
bias voltage at the zeners before..I suppose they're different with the 
plate transformer disconnected? I was expecting there to be a 2x 
difference in the CW and SSB settings, but it was more like -4.2v and -4.9v

thanks again,
kevin
AD6Z