Matt
I though that the messages were interestingly related, too!
The modification information was in an early 1982 QST as I recall.
Unfortunately,
I do not have this issue. The parts for the mod had been in a kit from Drake.
It's not a terribly difficult mod, but it isn't trivial, either.
May I assume the arcing occurs when you are transmitting into a dummy load?
Not
with reference to QRM, but to a stable -j(R).
A number of reactive load conditions, copuled with older tubes, could cause
this situation. More likely, though, is a component failure. Once the
dielectric on a part has failed from a previous arc, the carbon thus
deposited will continue to foster the condition, even when it would otherwise
not normally occur. A similar phenomemon occurs on high-tension power line
insulators.
How old are your tubes?
I have found several sets of stored Eimac 3-500Z tubes for anywhere between
$200
and $300. No guarantees.
New, guaranteed (Chinese) tubes cost about $110 each from RF Parts;
upgraded and
matched pairs cost about $250. French Amperex graphites cost $175 each.
Website:
http://www.rfparts.com
I personally think putting Chinese tubes into an L7 is like taking a Renoir
and
putting it into a plastic frame from Wal-Mart. But, the RF Parts brand are
guaranteed, very durable, and cheap. A third option is to wait for the
Svetlana
3-600Z which is due out in about a year. French tubes are an acceptable,
if expensive,
moral compromise. The graphite bottles need a bit more drive than the
'regular'
versions, so keep this in mind. Also, the Drake will require a reset of some
trimmers to set the idling plate current with tube models other than the
same type
which you have removed. The procedure is covered in the L7 manual.
I have the pulls from my amp. They are 1976 date code Eimacs, and make
full power
on 160 and 80/75. Gain drops off after that. I would be willing to lend
them to you
so you could test with tubes that are known-good and 'burned in.' In
return, I'd
only ask that you cover the shipping/insurance costs. Would this help at all?
Steve KZ1X/4
* * *
At 09:25 PM 8/2/98 -0600, you wrote:
>Steve,
>
>What a coincidence that we would start threads within 15 minutes of each
>other that are titled almost identically yet are totally unrelated otherwise.
>
>
>Anyway, I havent received any responses yet. My L7 is putting out about
>700 watts on 15--17--20 meters, but arcs on 40 and 80. It doesnt have the
>10 meter mod. I need to locate an article on how to do that.
>
>Good luck and 73,
>
>Matt--K7BG
>
>
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