Thank you all for the replies.
The blown fuse is the 2A fuse in series with the step-start current limit
resistor, not an input fuse. I don't think the the relay has failed with
the contacts closed (welded); the failure is such that the current limit
resistor is in the path long after the relay would normally close, shorting
the resistor and fuse. Also, if the step-start is operating normally,
there should be no current through the fuse independent of what the tube is
doing.. So it doesn't seem that any kind of tube failure could be the
cause.
I'll look at the rectifier / filter components to see if they develop 12v
after the several second delay. I'll let all know what I find.
John, K8DIL
On Fri, Nov 28, 2014 at 6:59 PM, Kim Elmore <cw_de_n5op@sbcglobal.net>
wrote:
> If you simply remove the tube and problem persists, it's not the tube.
> Given what you saw, I doubt the tube is the problem.
>
> Kim N5OP
>
> "People that make music together cannot be enemies, at least as long as
> the music lasts." -- Paul Hindemith
>
> On Nov 28, 2014, at 14:37, "Jim W7RY" <w7ry@centurytel.net> wrote:
>
> Or a shorted tube will take out the step start fuse and resistors.
>
> 73
> Jim W7RY
>
>
> -----Original Message----- From: Carl
> Sent: Friday, November 28, 2014 12:49 PM
> To: John DiLorenzo ; amps@contesting.com
> Subject: Re: [Amps] AL80-B fuse F101 blown;step-startnot working?
>
> The first thing Id check is to see if the relay contacts are welded,
> Ameritron uses the wrong contact alloy for high current use. Also check
> that
> the step start circuit is wired per the manual as Ameritron amps had a
> history of miswiring that could take out the transformer going back to the
> AL-80A and larger amps. Dont expect to find Ameritron issuing a bulletin or
> admitting a problem.
>
> If the relay is good then disconnect the HV AC from the rectifier circuit.
> If the fuse blows again then the transformer is likely cooked or there is a
> problem on the optional jumper terminal strip.
>
> Carl
> KM1H
>
>
>
>
> ----- Original Message ----- From: "John DiLorenzo" <
> john.dilorenzo33@gmail.com>
> To: <amps@contesting.com>
> Sent: Friday, November 28, 2014 2:48 PM
> Subject: [Amps] AL80-B fuse F101 blown;step-startnot working?
>
>
> I acquired this amplifier about two weeks ago, and when I received it,
>
> neither theforward nor reflected power meters would indicate anything. As a
>
> "test", Ireplaced the detector diodes (D114 and D115) with 1N914s as these
>
> were diodes I had on hand. My intent was to see if the meters would at
>
> least register something, and if so, order the correct diodes (1N34s).
>
> Well that worked,so I ordered the diodes.
>
>
> They arrived, so I replaced the 1N914s with the correct 1N34s. With the
>
> unit all buttoned up again, I noticed while tuning up, the meter lamps
>
> would dim, and the HV would sag significantly. I wanted to test and record
>
> some values when the amp shut down completely; this is what I had to that
>
> point:
>
>
> HV
>
> (volts) Ig
>
> (mA) Ip
>
> (mA) Standby 3050 0 0 Keyed, no drive 3050 0 0 CW, 5W drive 2700 20 125
>
> I discovered that F101 had blown in the amp. This fuse is in series with
>
> the step start resistor, so it seems my step-start was staying in the "low
>
> current" mode, and when I keyed the amplifier, this 2A fuse blew as
>
> expected. I'm just not sure what broke. The diodes I replaced aren't near
>
> the rectifying diodes that pull the step-start relay. Any insight into
>
> common failures, where to start looking, or how to debug?
>
>
> Thanks in advance,
>
> John, K8DIL
>
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