Hi to all
What does the say abt HV ??
I'll say take the tube out and check the pin connections
Schematics on the internet.
1. if g1 shorten to filament
2 Are both ends of filament connected
3 There isn't a connection fram Anode any pins !
>From a finds Amp
I have here a failing tube 3CX1200A7 from AL1200 there have been sending on
wrong band with
One ends of filament has been disconnected and are nw in contact with g1
Zeners was replaced too to a 50W type and 2A fuse insert to catode DC
connection
73 Boye
----- Original Message -----
From: "Carl" <km1h@jeremy.mv.com>
To: <TexasRF@aol.com>; <w5ghz@yahoo.com>; <amps@contesting.com>
Sent: Tuesday, October 19, 2010 3:57 PM
Subject: Re: [Amps] AL-1200 debug at a distance: we might have
awinner(W5GHZ)
> Both comments below are true if they were singular events. This amp seems
> to
> have had a singular IED leading to multiple failures which is pretty
> common
> when an Ameritron lets loose.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: TexasRF@aol.com
> To: km1h@jeremy.mv.com ; w5ghz@yahoo.com ; amps@contesting.com
> Sent: Tuesday, October 19, 2010 9:38 AM
> Subject: Re: [Amps] AL-1200 debug at a distance: we might have a
> winner(W5GHZ)
>
>
> Carl and all, if the plate choke opened, there would be no plate voltage
> or
> current alright. But, with drive, the grid current would be there in
> abundance.
>
> 73,
> Gerald K5GW
>
> An open bias zener would put full bias on the tube and there would be
> no plate or cathode current.
>
> A shorted zener would result in *LOTS* of plate current.
>
> A good zener will produce a specific bias voltage that allows the
> plate current to be somewhere between "not enough" and "too much".
>
> Don W4DNR
>
> --------------------------------------------------------------------------
>
> In a message dated 10/19/2010 8:25:37 A.M. Central Daylight Time,
> km1h@jeremy.mv.com writes:
> If the arc was one of Ameritrons IED events the plate choke may have
> opened,
> a fairly common occurance as the tube is prone to parasitics. Also check
> the
> safety choke on the back of the Tune cap.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "Hal W5GHZ" <w5ghz@yahoo.com>
> To: <amps@contesting.com>
> Sent: Tuesday, October 19, 2010 3:07 AM
> Subject: Re: [Amps] AL-1200 debug at a distance: we might have a
> winner(W5GHZ)
>
>
> It seems to be a common failure mode, Kevin. That arcing was most likely
> what you heard. If you can, clean up the mark left by the arc with some
> very
> fine wet/dry sand paper or emory cloth, about 800 grit. It should polish
> the
> metal, not scratch it. That will lessen the chance of another arc in the
> same place. An arc always leaves a carbon path and that leaves a low
> resistance (relative) path for another arc to occur. If the arc isn't too
> deep, you can often clean it up.
>
> Hal
>
> --- On Tue, 10/19/10, Kevin Normoyle <knormoyle@surfnetusa.com> wrote:
>
>
> From: Kevin Normoyle <knormoyle@surfnetusa.com>
> Subject: [Amps] AL-1200 debug at a distance: we might have a winner
> (W5GHZ)
> To: AMPS@contesting.com
> Date: Tuesday, October 19, 2010, 12:47 AM
>
>
> Hal W5GHZ suggested: "Check out the two Zener diodes above the filament
> transformer mounted on the wall.
> The high duty cycle may have burned out one or both."
>
> Other people seemed to point in the same direction, as they suspected I
> was
> saying "no grid or plate current" when
> keyed. (which was true: zero.)
>
> I unconnected the filament transformer and did some measurements.
>
> The AL-1200 schematics apparently aren't up to date in the manual online.
> I
> have a 2002 vintage rig, and the transmit
> relay was changed then. That new little board requires 14v and 28v so they
> changed the full wave rectifier shown in
> their meter board schematic to something with two diodes that gives 14v
> and
> 28v (plus two 2200 uf electrolytics).
>
> At first I thought those two little diodes must be what I was looking for.
> (not! although output from there serves to
> hold in one of the two older style relays on power on).
>
> I also checked all the relays for movement and they seemed good. You can't
> see the new transmit relay, but I could feel
> it clicking softly.
>
> The two zener's are stud mounted with insulators on the mid wall, I guess
> for heat dissipation. The back side is right
> by the tuning cap. I didn't want to mention that I heard a buzzing in the
> amp and backed off on the drive at one point.
> But the amp didn't die then, so I thought that wasn't a contributor to
> when
> it failed (looks like there's a little
> arcing on the brass tab that protects arcing in the tuning cap though..I'm
> wondering if that's what I heard, although it
> kind of looks old).
>
> Last year we had a long discussion about AL1200 and rtty and temp and I
> had
> done a lot of measurements on temp rise (in
> my setup) while CQing for a half hour straight into a dummy load, with
> temp
> probes so I could gather and plot temp rise
> data. I was confident I wasn't going to cook the tube from that data. (for
> my cooling situation).
>
> So back to the zeners. They don't seem mounted in the best place for heat
> dissipation. Maybe they actually get hotter
> because of where they are mounted! They had very dried out thermal
> compound
> on the insulators.
>
> The first zener is shorted by the CW/SSB switch. The second zener is in
> series with that one. So if the second one
> opens, you're dead for sure? (no bias?)
>
> So I measured the voltages, and the second one was definitely open. The
> first one at first I guessed was okay since it
> measured 5.6v.
>
> Looking at the current Ameritron parts list on
> http://www.ameritron.com/Product.php?productid=AL-1200
> they list them as 10W diodes (if mounted with low thermal resistance)
> DIODE, ZENER, 7.5V, 1N2971A, DO-4,10W, STUB MOUNT
>
> The 5.6v on that first zener dropped to .8v when the amp was keyed, so I
> suspected that Zener was bad somehow also.
>
> I totally removed the zeners to measure to be sure.
> The second one was an open in both directions.
> The first one was 360 ohms in both directions.
>
> So both were bad, but in different ways? (one open, one semi-shorted)
>
> I won't know for sure that this is the problem till I get replacements,
> but
> this is encouraging.
> So maybe Hal doesn't get full points till we know for sure.
>
> Thanks everyone! It'll be great if this is the problem (and not a $1300
> tube
> replace)
> Hey: any suggestions on a better replacement than the 1N2971A?
>
> Should I get a better zener diode manufacturer than what Ameritron sells?
> Maybe just better attention to the thermal
> mounting?
>
> Be interesting to know how common this is.
>
> -kevin
> AD6Z
>
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