[Amps] Drake L-7 arcing on 80m

[Carl]

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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