[Amps] Drake L-7 arcing on 80m

[Alek Petkovic]

G'day Bill

Do as Carl suggests.

A friend, VK6RK, had a L7 with the exact same symptom. In his case, 
you could actually hear the plates rubbing or touching when the 
amplifier was switched off as well.

He tried everything to get at the capacitor and straighten the plates 
but in the end, he had to bite the bullet and take the whole bloody 
thing out and do it on the bench.

The amp works very well now, so the time spent was well worth it as 
he picked it up at a basket case price.

73, Alek.
VK6APK

At 02:10 AM 19/05/2010, Carl wrote:
>Take the cover off, bypass the interlock, and do a visual when in operation.
>There could be a switch problem or fixed cap causing the variable to arc.
>
>Carl
>KM1H
>
>
>----- Original Message -----
>From: "Bill Dzurilla" <billdz.geo at yahoo.com>
>To: <amps at contesting.com>
>Sent: Sunday, May 16, 2010 12:55 PM
>Subject: [Amps] Drake L-7 arcing on 80m
>
>
> > Hello,
> >
> > I recently acquired an L-7 amp and I tried it out
> > yesterday.  I used my Pro II as the exciter, an amp
> > keyer, and a dummy load.
> >
> > There seems to be some problem on 80, unfortunately.
> > On all bands, I started with 20 watts drive and slowly
> > increased the drive while tuning for max output.  When
> > I got up to about 600 watts out on 80, I heard and saw
> > through the meter a blue arc.  This happened twice on
> > 80, and I did not want to try it again.  No arcing at all on 40, 20, 15,
> > or 10.
> >
> > I opened up the amp and everything looks OK, except for one of the 25 or
> > so stators on the plate tuning capacitor has graffiti-like white traces on
> > it.  I suspect this is the source of the 80m arcing, as the rotor does not
> > go over the spot with the traces when set to 40m and up.  I have not tried
> > the amp on 160m, but if my theory is correct it would arc on 160 as well
> > as 80.
> >
> > The capacitor plates are not dented or deformed in any way.  Have not
> > tried the amp on the WARC bands.
> >
> > So, do you think the stator is the source of the problem?  If yes, is
> > there any fix?
> >
> > 73, Bill NZ5N
> >
> >
> >
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>
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