After cooking the valves now they work correctly I am describing my
?Cooking Recipe? if it is of any use for other ham with the same problem.
I have followed Bill?s instructions, and I have been cooking each valve one
by one.
First with the HV disconnected (this is easy with the L7 but you have to be
very careful) left it for about 20 minutes with only filament voltage, after
that I connected back the HV (again with the amp unplug from the mains).
Switch on the mains, this time using a Variac at about 180v and gradually
going up to 220v, left it in STBY for 15 min.
I did repeat the same procedure with the other valve, and after exactly the
same with both valves. I left them on STBY for 12 h.
Now the valves work at full power with no Bangs or other problem and I can
get about 200 or more watts than with the older ones, just as new, hope they
will keep that way for long.
Well now next problem,I have to think in climbing to the tower to see what
happens with my Tail-Twister it refuses to turn and today is quite cold for
Mallorca, 10 deg .
Thanks to all, Jaime.
-----Original Message-----
From: Bill Coleman [mailto:n2bc@stny.rr.com]
Sent: Saturday, November 13, 1999 3:12 AM
To: Jaime P.Ullívarri
Subject: Re: [AMPS] 3500Z Bang!
Jaime, sounds like one of them is shorted... from transporting it, or???
You could possibly see a grid to filament short with an ohmmeter. Ohm them
both out first to rule out gross level problems.
After that, I would try one at a time. Cook each with filament voltage only
for 30 to 60 minutes, then use your variac to gradually bring up the plate
voltage.
Be careful in there!
GL Bill de N2BC
----- Original Message -----
From: Jaime P.Ullívarri <EA6NB1@teleline.es>
To: <amps@contesting.com>
Sent: Friday, November 12, 1999 1:43 AM
Subject: [AMPS] 3500Z Bang!
Hi all,
I have bought from a friend a couple of Eimac 3500Z ( from 1989.) as spare,
the owner says this tubes only have been in use two times he check them on a
Heathkit amp and they were good.
I have inserted them on my Drake L7 on CW mode and after less than a minute
being on SBY a BANG! And no HV.
A resistor in the PS was exploded; it was R12 (IRC type BWH .82 ohms 2W) I
had one of these resistors and after replace and putting back my old tubes
now the amp is Ok again.
There is not any visible anomaly on the tubes also a have check them with a
tester and tapping them, all OK, I have no Hi Pot.
Tomorrow I am going to try again but using a Mains variable trans former
starting with 100v mains and trying to cook them on SBY.
There is any problem with that? I will appreciate any help.
Best 73, Jaime.
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