[Drake] L-75 output?

[Jim W7RY]

1st of all... 100 watts drive to a single 3-500 is WAY TOO MUCH!!  Look at 
your grid current when you drive it that hard! I bet it's over 200+ 
mA.   The MAXIMUM grid current on a 3-500 is ~120mA.

Limit your drive to 60 watts max. With this drive, it should put out about 
600-800 watts. Remember the plate transformer on a L75 is not that large.

How much power does the average L4B or L7 typically put out?  My experience 
is about 1300 to 15000 MAX!  Just take half of that and you have when the 
L75 should have for output power. This statement also goes for the drive 
power as well!!.

With the high drive power it may be that the 3-500Z is just tired of being 
driven that hard??  Overdrive strips the cathode and rather quickly, 
especially during tune-up and testing.


Good luck
73
Jim W7RY



At 03:46 PM 11/28/2004, Tony Sokol wrote:
>Hi Gang,
>    Recently I was fortunate enough to acquire a spotless L-75 amp which 
> is one of neatest little amps out there.  This one is definitely a 
> keeper.  (Unless I luck into an L-7)   :-)   I do have it wired for 120 
> VAC on a very stiff dedicated line.  ( I can get well over 1500 out of my 
> 30S-1 on the same line.)  In measuring the the power out of the L-75 I am 
> seeing almost exactly 1000 watts  on 75 and 40 and more like 750 watts on 
> 20.  From what I have been able to glean from looking at reports on other 
> single 3-500ZG amps this looks pretty typical except maybe for the drop 
> off on the 20 meter band.  I am using 100 watts to drive it and the plate 
> voltage is a little over 2500 under full load.
>    I am tempted to pick up an RF Parts 3-500ZG to see if things improve 
> since I really do not know how this one has been treated.  I know that 
> the guy on the other end will never see the difference but I enjoy 
> getting get things right up to snuff just for the fun of it.  Also, I 
> think my 3-500ZG is a pull since the one pictured in the amp before I got 
> it was an Eimac and this one has a graphite plate.   Anyone else have 
> experience with single 3-500's along this line?
>        73
>Tony - W9JXN
>
>
>
>
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