With a shorted and open zener there will be some conduction depending if its
CW or SSB position. You already stated there was a very low bias earlier
which should mean the tube is conducting.
By multiple issues I mean zeners, tube, safety diode, plate choke,
bandswitch, meter, protection circuitry, and more can all fail during an
Ameritron IED.
Try concentrating on the suggestions and skip the zener wattage and other
non pertinent stuff that makes for hard to follow replies.
Carl
KM1H
----- Original Message -----
From: <knormoyle@surfnetusa.com>
To: <amps@contesting.com>
Sent: Tuesday, October 19, 2010 3:14 PM
Subject: [Amps] AL-1200 debug at a distance: we might have a winner(W5GHZ)
> Boye posted from a search
> "Zeners was replaced too to a 50W type and 2A fuse
> insert to cathode DC connection"
>
>
> This is interesting because I was also looking at the
> 50W zeners and wondering if the 10W might be undersized.
>
> The 10W diodes are only rated to 10W up to 50C. at
> 100C, they derate to 6-7W.
>
>
> Couple that with poor thermal mounting and they might
> not take much at the high internal temps of the amp?
>
> The 50W versions need a larger mounting hole (1/4")
> which is doable, but I'd also need the 1/4"
> insulating hw.
>
> I replaced a cooked final transistor in an icom 756 a
> while back with a NTE part and it seemed to work well.
>
> So I thought maybe I'd try NTE parts here. I ordered
> two NTE5182A (7.5 volt 10W) and am going to use them.
> (while ameritron and rfparts sell the 1N2971A, it
> seems not widely available)
>
>
> The non-switched diode was definitely open. I don't
> think I had any excessive grid current events...well,
> I guess none that would be visible on the meter.
>
> I'm not sure about the suggestion of evidence of
> multiple issues. No evidence of that yet?
> The no plate or grid current is consistent with an
> open on the non-switched diode, right?
>
> Now if the non-switched diode was shorted, that would
> be a different story.
>
> Thanks for the info on the other diodes to check.
> Will check them.
>
> Thanks for all the comments everyone. It really helps me.
>
> -kevin
> AD6Z
>
>
>
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