Greetings
I am re-posting this message with the hope that some of the "experts"
here will take some time out from sniping at each other and answer a
real question concerning a amplifier design problem.
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:
www.svetlana.com/docs/TechBulletins/technoteNO.32.html
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 24 volts at 50 watts. should
this be changed? suggestions? ( I did have some correspondence with
one person who seem to indicate that this xener has been a problem in
his LA1000.)
After studying the schematics for the amps I have noted that the 6MJ6
has the first grid connected to the cathode. The other grids
(suppresser) are connected to ground.
In 6LQ6 in the Dentron has all three grid tied to ground. What effect
would this have on the operation of the EL 509 .
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.
The power supply is rated at 1200 watts SSB 1100 v supply. There is
also the possibility of using the power supply from the dentron in
series with the amp supply transformer to get more voltage. Any
suggestions on a relatively inexpensive tube would be welcome.
I am sure that I have missed something else that needs to be checked
so any suggestions would be appreciated.
Thanks
de John KA4U
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