Mark McCloud wrote:
>Since I was replacing the 10ohm 12w resister I thought I would go with
>something a little beefier so I had a 25w part in stock.
>Well, I turned it on and the resister slowing blistered before I turned
>it off. Back to the drawing board.
>Any thoughts?
>Mark
>K6YCV
>
Almost certainly, the root cause is that the step-start relay is not
operating. This leaves the resistor permanently connected in series with
the mains, so the original 10W resistor blew and the 25W replacement
gets very hot.
Look for the cause of the relay not pulling in. It may be the relay coil
has failed, but it's more likely to be one of the other components
around the relay. (Sorry, I don't have a schematic, but others on this
list will have more direct experience.)
When you have fixed that problem, wire a 2-amp SLOW-blow fuse in series
with the resistor. When the step-start is operating normally, this fuse
will never have enough time to blow, but if the step-start should fail
again, the fuse will blow after a few seconds to protect the resistor
from cooking. (I believe the credit for this idea goes to Alpha.)
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
>
>----- Forwarded Message ----
>From: Mark McCloud <k6ycv@yahoo.com>
>To: amps@contesting.com
>Sent: Sunday, April 13, 2008 8:00:46 PM
>Subject: AL-80A Problem
>
>
>Thanks to all who responded. Upon further investigation I found the
>resistor (underneath the Interlock switch)
>has blown. I couldn't find it on my schematics but did find it on a
>copy that had the Step-Start revision with Buck-Boost
>(10ohm @ 12 watt). I assume that this was added at a later time.
>
>Is 10 ohm @ 12 watt enough? I'm running the amp @ 115 vac with a 756 Pro.
>
>73's,
>Mark K6YCV
>
>
>Hi All,
>
>I have an AL-80A that has developed a sort of momentary shutdown. I
>have it connected to 115vac.
>I noticed a momentary "snap" after it was turned on for a while but
>wasn't sure it was coming from the amp.
>Later it developed the momentary loss of HV but came back immediately.
>In fact, the HV meter never dipped more
>that a few hundred volts while idling before coming back to about 2900
>volts. I took it off line and popped the cover to look
>for anything that looked or smelled bad. Nothing found so far.
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>Amps@contesting.com
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