On Mon, Jul 2, 2012 at 8:25 PM, Bill Turner <dezrat1242@yahoo.com> wrote:
> ORIGINAL MESSAGE:
> On Mon, 2 Jul 2012 19:39:18 -0700, you wrote:
>
>>
>>In a fit of haste/stupidity/DX-angst/all-of-the-above, I popped the
>>plate choke in my AL-1200. It made a nice *crack* when the stray wire
>>hit the casing of the blower ;)
>>
>>I see that Ameritron have the replacement choke listed at $20, and RF
>>Parts have one for $24.95. Is the RF parts one any better?
>
> REPLY:
> Any idea what blew the choke? An arc? Broken wire? Something else?
I was trying to tune up at the time (after not having used the amp in
a couple of months). I didn't seem to be getting as much out as I
should have, then it went BANG. I (stupidly) wasn't watching the Ip
meter, and am fairly sure it blew due to excessive current... but I
may find some other problem when I get the new choke installed.
> I have used the RF Parts chokes in several homebrew 1500 watt amps
> with no problems. It really does have no resonances in any ham band
> from 160-10 including WARC.
>
> One thing I would advise: Don't mount the choke where capacitance
> coupling to the tube anode might be a problem. Either place a shield
> between tube and choke (preferred), mount it far away (not
> recommended) or orient it 90 degrees to the tube. Placing it where
> there is significant capacity coupling between anode and choke creates
> a secondary circuit with some potentially bizarre characteristics.
There is such a shield in the AL-1200. You can see it here:
https://secure.mfjenterprise.com/pictures/AL-1200t.jpg
73,
~iain / N6ML
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