[JMS] 90801 help

Fri, 19 Dec 2003 11:40:25 -0700

Ronnie,

OK, I downloaded the schematic from the Millen Society page, so now I =
can see what you are looking at.  It would be best if you could get a =
copy of the Manual for the 90801, that would tell you for sure what to =
do with the various terminals.  I didn't see one listed on the BABA =
page, but I'm sure you could get a nice one for a few bucks from one of =
the folks who sell manual copies.  For example HI Manuals now owned by =
Surplus Sales of Nebraska should have it.  Look at www.wurplussales.com. =
=20

Now for some guesses. =20

On TB1, Gnd is obviously the ground point.  Connect one side of the 6.3 =
vac for filaments and your power supply grounds here.

C- is the bias return point for the 6146 control grid.  Depending upon =
how you want to key the rig, you might want to supply some "battery =
bias" to the 6146 here or you might just want to connect this point to =
ground.  If, for example, you decide to cathode key both the 6146 and =
the 5763 together, just ground this terminal.  If you decide to key only =
the 5763 and let the 6146 run all the time, put enough bias on this =
terminal to keep the 6146 cut off or nearly so when it has no drive from =
the oscillator.  As a guess, -45 volts would do.  The + side of your 45 =
volt supply would then go to "ground."  You could also use this point to =
arrange for grid block keying of the 6146 if you wanted to. =20

6.3V is the filament supply connection.

"1" is connected to the HV terminal through R10 and R11, a total of 31K =
ohms.  My best guess is that if you want to run the rig off a single HV =
supply rather than a HV and LV supply, that you should jumper "1" to =
"LV."  My Millen 90800 has internal resistors like this that let it run =
from a single HV supply.

LV is where you would connect a "Low Voltage" supply, around +300 volts, =
for the 5763 oscillator if you don't use the jumper to "1" described =
above.

HV is where you would attach your High Voltage supply, whatever you get =
out of your 800 vct transformer and rectifier/filter would be fine. =20

on TB2, 5763 C- is the bias return point for the 5763 oscillator control =
grid.  Again, what you do with this point depends on how you decide to =
key the rig.  If you want to cathode key the 5763 (with or without the =
6146), just ground this point.  If you want to grid block key the 5763, =
return this point to a negative bias voltage, -45 volts or maybe more, =
and arrange a way to key it to ground potential without shorting out =
your bias supply. =20

"Screen Resistor" (terminal 3) looks like the 6146 screen resistor.  =
Normally I'd jumper this to terminal 4, "Screen."  This would also be a =
point where you could key the 6146, but if you do use a relay to keep B+ =
off your key.

"6146 Cathode" (terminal 5) - a convenient point to key the 6146.  You =
could let the oscillator run all the time, switching it on and off with =
the HV or LV supply switch for example, and just key the amplifier by =
itself, or you could jumper this terminal to "5763 Cathode" (terminal 6) =
and key both of them together.  You could also provide some fixed bias =
to the 6146 control grid as described above, ground the "6146 cathode" =
and key just the "5763 cathode" to ground.  You have several options to =
try out. =20

In any event, when keying cathodes to ground, be aware that substantial =
B+ will show up on your key.  The safest thing to do is to key cathodes =
through a relay.  The next best thing to do is to arrange the wiring to =
your key so that the body of the key is on the ground side and the =
cathode is connected to the bottom contact of the key.  The "swinging" =
contact connected to the moving key arm and to the body of the key =
should be at ground potential.  That will give you the best chance of =
keeping your fingers out of the high voltage on the key, and it's what =
most of us did back in the 50's with cathode keyed transmitters rather =
than spring the dollars for a keying relay.

I hope all of this helps.  If it doesn't, declare the little rig a lost =
cause and send it to me.  HI HI

73,

Jim Hanlon, W8KGI

  ----- Original Message -----=20
  From: w5sum=20
  To: [email protected]=20
  Sent: Friday, December 19, 2003 7:20 AM
  Subject: [JMS] 90801 help

  well I have become the proud father of a fairly nice 90801. I plan on =
using=20
  this for a driver for a 813/805 homebrew rig.
  all I have is a schematic and there is a might of confusion here.

  There are two terminal strips on back. TB-1 and TB-2

  the schemtic  shows TB1 to have ground, -, 6.3v, 1(???), LV and HV. I =
think I=20
  can figure out those voltages for a 6146. I would like to know what =
the=20
  terminal marked I or 1 is for?

  Now.. TB-2   what goes here? I see where it is marked 5763 C-, Screen=20
  resistor, screen, 6146 cathode and 5763 cathode, then ground.

  HOW does one hook everything up to this?

  I have a power transformer that is 800V centertapped that should give =
me what=20
  I need, though maybe lower B+ than I would like, but it will suffice. =
All I=20
  will need is perhaps 20 watts of drive for the Class C 813's

  hep me hep me

  Everyone have a very Happy and Safe Holiday Season

  Thanks in advance

  Ronnie - W5SUM

  The "AM" voice of Shreveport, Louisiana USA
  formerly WN5AIA and WB5AIA
  I got my Extra Class the old fashioned way... I earned it!
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