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[AMPS] Amp Supply LA 1000 options?

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Subject: [AMPS] Amp Supply LA 1000 options?
From: (John Simmons)
Date: Tue, 10 Oct 2000 19:47:07 -0400
 I have some question  regarding  amplifier modifications and design
changes.   I am not a electrical engineer so I do need some help when it
comes to understand the scuttle in's and out's of amplifiers.
I have recently acquired a Amp Supply  LA 1000  amp. This amp will
replace a Dentron GLA 1000 .    I converted the Dentron to use the
Svetlana EL 509 tubes.    The  reason for making the change is that the
LA 1000 has 160m meter as well as  tuned input for all bands and the
unit can be power from 240 volts.
For the Technical information on the GLA 1000  conversion see:
I am wondering if any one has made this conversion on the LA 1000 amp
and what problems were encountered.

The LA 1000 currently has some dead 6JE6C  ( 6LQ6) .   The manual calls
for a 6MJ6.   I have not been able to find much information on the tubes
except that they all have seem to have a common base diagram 9QL
I am wondering if the EL 509 will work in place of the 6MJ6  after
rewiring the tube socket to match the  9RJ base diagram.
Diode D2  bias the tube at ( this is a guess)  21 to 25 volts.   should
this be changed?  suggestions?

The article  mentions shorting one turn on the tank coil and adding 200
pf to the out put of the pi network
I  don't know if this would be necessary with the LA 1000 and would
appreciate any input into what modifications should be made to the tank
circuit.    I do have the MFJ-259 swr analyzer and thought about opening
the output circuit and inserting a resistor to simulate the tube .
The Svetlana data sheet indicates that the nominal plate resistance is
8000 ohms.   Would 8000/4=2000 ohms be  the correct value to use here.

I have also noted that the parasitic plate chokes are missing for this
unit.      I do need to know what is needed here as the manual does not
indicate what the values are.

Will the ATI-6 input network need to be re-tuned or can it be
re-tuned?   I have a MFJ -259  swr  analyzer and though I would  open
the input to the tube and inset a resistor to simulate the cathode
circuit if that will work ?   The question is what would the resistor
need to be?   Svetlana indicates the grid to cathode is  25 pf.   It
would seem to me that tube impedance varies as the frequency changes or
am I missing something.

I would not be adverse to dumping the 4 EL 509's in favor of a single
tube provided that the changes would not be to complex.
The power supply is rated at 1200 watts SSB   ( 1100 v @ .6 amp cw dc
input)  Any suggestions on a relatively inexpensve tube  would be

I  am sure that I have missed something else that needs to be checked
so any suggestions would be appreciated.

de John KA4U

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