The first place I would look is the coax,cable from the ant. relay to the
output connector. I fought an amp , (not an al811) sometime back for quite
some time before I decided to look in that area. It isn't the only place ,
maybe but it is one of many, and it's just not too obvious either!!!!!
disconnect the rf choke on the output side and measure from the output
connector to ground.have fun!!!!
carl / kz5ca
----- Original Message -----
From: "Steve Katz" <stevek@jmr.com>
To: <Wt8r@aol.com>; <amps@contesting.com>
Sent: Wednesday, October 03, 2001 10:34 AM
Subject: RE: [AMPS] Problem with AL-811H
>
>
>
>
>
> > I am attempting to repair an AL-811H for a friend. The amp has been
> > abused due to mishandling as aircraft baggage making several trips to
the
> > Caribbean and back. The outer case shows several dings and one of the
> > threaded holes in the chassis metal which holds the cover in place has
> > been broken open.
> >
> > The reported symptoms are: When attempting to tune the amp upon return
to
> > home QTH, there was a pop and a flash inside the amp.
> >
> > ::Sounds like someone took a picture. Did you pose?
> >
> > On my bench, I am driving the amp using an Icom 751-A. The only visible
> > signs of damage evident to any of the electronic components was one of
the
> > two 1000pF DC blocking capacitors from the anode/plate RFC to the tank
> > circuit was cracked open slightly. I replaced these with two 500pF (6KV)
> > capacitors for test purposes with no apparent difference in result.
Using
> > an ohm meter, it appears that the DC input blocking capacitors at the
top
> > end of the filament RF choke are good and that no short circuit to
ground
> > exists on the input. The tubes show no internal shorts using an ohm
> > meter. The tubes light properly, the HV is 1700V and the anode idling
> > current when keyed (without drive) is 150 mA (which is about right).
> >
> > I disassembled the rear pc board from the rear panel and inspected the
> > traces for burns and shorts, but nothing was obvious.
> >
> > When attempting to operate the amp, the grid current and plate current
> > swing up and down in synchronism with the drive, but NO RF output is
> > observed. I am using a power meter and a Bird 2500 watt dummy load.
> > Adjustment of the TUNE and LOAD capacitor produce no apparent dip nor
> > power output. No unusual smell or noise is observed.
> >
> > ::This really sounds like a T-R relay not making contact, or possibly
not
> > even switching. I don't recall if the AL811H has a separate input relay
> > and output relay, or if they're all one unit; however, the symptoms seem
> > to indicate an open circuit between the plate tank and the coaxial
output
> > receptacle...
> >
> > Any suggestions would be greatly appreciated.
> >
> > Dave, WT8R
> >
> >
>
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>
>
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