[AMPS] Drake L7 and 'new' Eimac 3-500Z

[Steve Jackson]

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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