[Johnson] Cottter - forgot these *

[radioman]

not easily... This was published in ER..but I only have a schematic..
probably published in 1993 or before

here is what happens:

1. 6al5 and 6c4 are no longer used, coupling and decoupling and cathode
bypass caps are increased for more bass response and low distortion.

As before the two sections of the 12AX7 are cascaded  resistance coupled
voltage amplifiers, but now with different bias, and values.  The two
sections of the 12AU7 in paralell, continue to deliver a couple of watts
of power to drive the grids of the 6146 modulators through the original
driver transformer.


This sounds nice, but isnt the best for DX.
Mike gain is very high, and with the D-104 it barely requires 1/2 notch
of audio gain for 100+ACU- mod.  I tried to crank this back a bit by
changing the V-12B bias resistor from 1500 ohms to 2200 ohms.  Changes
beyond that would require audio test equipment to verify the results.

This is a wildcat set of plate load, grid, and cathode resistor values,
which I didnt develop..and which are at odds with any standard manual
values.  They do seem to work,

Use minimum specified wattage for  CARBON resistors.
V-15 has to deliver several watts of audio, and all that power must flow
through the cathode resistor.. dont go undersized.

Use  audio grade film capacitors... mylar, polypro, but not ceramic or
mica.
Tex caps or orange drops are fine.
Use NEW fresh minature electrolyics from Japan.. they last.
Dont use Old stock crap.

follow your schematic of the audio chain from left to right and pencil
in these changes:

c-62 mic coupling cap  from .005 to .02 film type 50 volts or more

c-79 coupling cap from .01 to .1 uf 400v  film type
r-26 plate load resistor from 47 k to 220 K  1/2 watt
c 76 plate decoupling from .1 uf to 15uf or 22 uf 450 v electrolytic
r 53 voltage divider from 220K to 47 K 1/2 watt
r-52 voltage divider from 47 K to 4.7 K 1/2 watt
r-29 cathode bias resisistr from 680 ohm to 2200 ohms 1/2 watt (critical
value)
add  cathode bias capacitor for V-12B pin 8,  10uf 25 volts
electrolyitc. neg end to grnd.
c-83  from .01 to .1uf 400v film
r-30 plate load resistor from 47 k to 220 k 1/2 watt
+ACo- Install shielded audio line from pin 6 V-12-B( after coupling cap) to
pin 7/2
of V-15

+ACo-add new grid resistor 470K 1/2 watt V-15 pin 2 to ground.
+ACo-add audio decoupling cap 22uf 450 volt electrolytic from secondary
centertap of driver transformer (V-15) to ground.

disconnect B to R-34 and R-35 to disable the clipper and 6C4
disconnect
r-43 pot from grid of V-15
r-45 cathode bias Pin 3 of V-15 from 820 ohms to 1k 2 WATTS +ACE-



+ACo- go through your transmitter and replace all the electrolytics in all 3
powersupplies with new units like NTE, Tex Caps, or Nichicons. Use
standard values in the powersupplies.

These component numbers are based on Valiant I.

Larry W6WUH