Mini-tube TX ( 6AU8 )

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From: CPQM Admin (CPQM_Admin@cpqm.saic.com)
Date: Sun Jan 16 1994 - 16:34:35 EST


Mail*Link(r) SMTP Mini-tube TX ( 6AU8 )
ANOTHER XMIT! ( will go with 6GH8 RX set and 150V power supply)

     6AU8 ( 6AW8 6BA8 etc, 9DX based tubes) Transmitter up to 700mw

                               :
            3 +----+--)(--+ : 9 +-----------+----+
             _|_ | .01 | : _|_ | |
   +---+-----... ) |C101: 7 ...------+ _|_ )
  _|_ | 2 --- ) +--)(--+----... 8 | ___.o1) L2
  [ ] < 1| )L1 | : | --- | | )
   |X1 >100k | ) \_|_C1 : < 6| | \_|_C2 ) +----------o out
  ### < | | --- : >56k +-)(-+-)(+ --- ) ( L3
       | c o |-)(---| \ : < |.o1 |.o1| | \ ) (
      ### J o |.01 ### : | < ### | ### | +-----+
          S1 o |b | :### > 100 | | |
            a| ### | : < ohms | | ###
  o----------+-----)------------------+ | |
key | | : | |
  o---+---)(-+ +---------------------------+-/\/\/\-+---o 150v 40ma
      | .o1 : / | 2200 2 | +
     ### /\ fil : +-->|--------+ 2 watts| o -
              4| |5 : | / 100v _|_.o1uf |
               o o : ### 10 w zener ___ ###
             6.3v .7a | |
                              ###shield ###

pf = uuf = mmf all caps => 250v
                                    Resistors 1/4 w unless specified & any %
.o1 = 103

C101 22 - 100pf...use smallest value that gives max out put...will need
                   to be 22pf for 3rd Over-tone xtals/ freqs 14mc and up

C1=C2= 50 uuf min (at max mesh) but not over 400uuf
                                200-400 uuf jobs good for 160-80-40 mtrs only

I used 55uuf ones from Fair Radio Sales....screw-driver adj.

L1=L2= (can be Digikey coils)

     C= half mesh value of C1 C2
     F= Mid band freq, Mc's 25330
                                      ---------------- = UH
                                         (F x F) x C
     round off to nearest std value
     that Digikey has.

L3 ... aprox 6:1 ratio, turns...experimental try n see may be needed

Note...on higher bands, osc may chirp so, use S1 to keep osc on & just key
       the final.

S1
       [ o o o ]
        a c b can be toggle or slide-switch

S2 ( not shown) DPDT...to switch ANT from RX to TX and switch B+ to
    transmitter if desired...or cross wire it to put dummy load where ant
      is not... ( pair of 100 ohm 1 watt in paralell)

    _____________
    | |
    < o o o---- TX
> 50 \ / I favour this method for T/R on QRP
    < / \
    | o o o---- RX
   ### |
                +----ant

Zener..In my model , I used a VR-105, later tried a stack of 9 volt 1 watt
       zeners ( by passed with .01uf 250v).
       Cost of all those 9's is close same as a sud-mtd 10watt 100v.

If using the 'improved 150v supply' you can omit 2200 ohm and zener, and
run a 2nd B+ wire, to the 100v...of which it can be the switched one for T/R
if you choose to switch the B+...( keep B+ ON, on the RX set tho).

The reason for being vague about C1 C2 is that everyone has their own
sources for caps... so for me to rock-solid-specify a uuf, may make it
impossible for some to build this.

For those who have caps or get caps of 2 different values, just calculate
the uh for each.....need NOT have to have both caps same.
...but put the smaller value cap on the oscillator (triode ) part.

This is NOT a wood base set! A 7" chassie (aluminum) is best, but those
wanting to build small, can squeeze it all in to a 5 x 3 Radio Snack box.

Pentode section of this rig may try to self osc...so have L1 and L2 mtd
on 90 deg. angle to each other....or as I did, put a cross-socket shield
so it passes between pins 1 & 9 and OK if it grounds pin 4 or 5...unless
same supply runs Receiver, and you want fil. line to be balanced.
( then slip sleeving over 4 & 5 to prevent shortage)

The central pin that many 9 pin sockets have can be used as solder-on-support
for the shield....cut a slot in the shield so it fits up in there.

The shield is to be cut carfully so it snug-fits the socket and has 'feet'
with holes to allow # 4-40 nuts/bolts fastening to the chassie.
I used a metal coffee can lid for this....cut to fit, using sissors!
( I got a cheap pair for $3.00 at Walgreens)

 Magnified view of cross-socket- shield: U cut to fit

      -------------------------------------------------------
      | |
      | |
      | |
      | |
      | O hole |
      | |
      | O hole () hole |
      | __ |
      | O hole | | slot for ctr pin |
      | | | |
      | _______| |________ |
      | _| |_ |
      =============== =================
      footy ^hole socket here ^ hole footy

Left & Right edges should contact the sides of chassie...using a bent L
like shape on the edges, to clear the installation of the cover if a
5 x 3 " box ( cover is U shaped )

O Holes allow wires to get thru for key-line, B+ and Filament

() hole is for passing the grid-side of C101 thru

C1 to be on triode side of shield, C2 to be on pentode side.

This ckt I made in 1989 to try for 10 mtr CW, but not having the right
crystal at that time, the ckt was relegated to just testing.
It lit up a #47 bulb about 3/4 full brite....which is about 700mw.

By the way, I use this trick for RF and IF amps too....even tho tube is
a single pentode.

To make this readable in one evening..not take all week, I'll stop here,
and any one needing details,including plans for the power supply, Email me.

--
Randy KA1UNW              If you get a shock while
                         servicing  your  equipment,         "Works for me!"
randy@192.153.4.200             DON'T  JUMP!                     -Pete Keyes
                     You might break an expensive tube!

------------------ RFC822 Header Follows ------------------ Received: by cpqm.saic.com with SMTP;15 Jan 1994 19:44:29 -0800 Received: by mail.think.com; Sat, 15 Jan 94 18:04:10 -0500 Return-Path: <randy@cyphyn.radnet.com> Received: from Think.COM by mail.think.com; Sat, 15 Jan 94 18:04:08 -0500 Received: from cyphyn.radnet.com by Early-Bird.Think.COM; Sat, 15 Jan 94 18:04:02 EST Received: by cyphyn.radnet.com (Smail3.1.28.1 #5) id m0pLJze-0001UyC; Sat, 15 Jan 94 18:01 EST Message-Id: <m0pLJze-0001UyC@cyphyn.radnet.com> From: randy@cyphyn.radnet.com (Randy) Subject: Mini-tube TX ( 6AU8 ) To: boatanchors@gnu.ai.mit.edu ((mail net) (boatanchor net)), qrp@Think.COM (qrp @think.com) Date: Sat, 15 Jan 1994 18:01:21 -0500 (EST) Cc: psc@colmiks.colmiks.com (aka (phil cook)), pjk@Think.COM (Pete at Myth), michael_nagorski@quickmail.cis.yale.edu (michael nagorski) X-Mailer: ELM [version 2.4 PL21] Content-Type: text Content-Length: 6601


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