Hi List!
Well, as title says, the L7 is again generating RF !. In order to arrive to
that point, I have first done some detective work... I have located the
original owner (as I did the buying from a relative of him) and talked with
him by phone. It seems that, as the amplifier had been lots of time unused,
before selling it, he did some operating checkings using a loaned Icom
transceiver (without AGC connection, I guess). Well, he checked over all
bands to be sure the amp worked fine. As he didn't have a larger dummy
load, he used a 500W job... He told me he didn't noticed anything wrong in
the amp while doing those tests. I trust him and think Murphy was waiting
for just last moment to blown the resistor...
Anyway, as tube failure was not evident (those checks were made about a
month ago), I have decided to do a 'real life' check, using the TR-7 at
about 10W output in AM mode as an exciter. Then I have found that my PS-7
(TR-7 power supply) is of the 'old' type, so the VOX connector is of an
special kind (two pin instead of RCA) which, of course, I didn't have (any
around, please?). So, as I had already built an RCA-RCA wire, I have
decided to activate the VOX by means of a shorted female RCA plug. First
check, without the shorted plug, showed about 2000V plate voltage (but it
was not applied yet to plates). Plate intensity was still zero, as it
should be... Then I have shorted the VOX line so the relay has been
activated. Plate voltage has dropped a bit and then plate current has gone
to about 170mA, where the manual says it should be. And no power supply
BANG!, which was what I was afraid... So I have put some RF and dipped
plate current, getting about 200W out from 10W in. I have not put in more
power as I am not sure how much the antenna will take and also because the
linear was uncovered and I didn't want to take any chances. If it works
this way, it should work with more power, I guess. Anyway, next step is to
enable interlocks, put the linear cover and try again with some more power.
It would be fine to locate the missing two pin VOX connector... any source?
Well, all in all, I am very happy!. Thanks for all your help.
Regards,
JOSE
----------------------------------------------------------------------
73 EB5AGV / EC5AAU
JOSE V. GAVILA
La Canyada - Valencia (SPAIN)
EB5AGV Vintage Radio Site: http://www.geocities.com/eb5agv
European Boatanchors List: http://www.eGroups.com/list/euro_ba_swap
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|