Glen Zook gzook at YAHOO.COM
Fri Nov 24 13:34:26 EST 2006

There are a couple of no wiring changes modifications
that you can make to the internal VFO in the DX-100
that greatly improve the stability.

The first is to replace the 6AU6 tube with a 6AH6. 
Heath did this in the Apache (earlier versions used
the 6AU6) which helped considerably with the
stability.  This is a direct replacement.  The only
thing that may be necessary is to increase the
capacity (very slightly) on the variable capacitors
that are used in the calibration.  This is due to the
fact that the internal capacitance on the 6AH6 is
slightly less than that of the 6AU6.  However, even
when the oscillator tube is replaced with the original
type 6AU6 you often have to adjust these capacitors
slightly to maintain the calibration.

The second is to replace the 0A2 regulator tube that
controls the screen of the oscillator tube with an
0B2.  This drops the voltage from 150 volts to 108
volts on the oscillator tube which also helps
considerably with the stability.

A modification that requires a slight rewiring is to
regulate the plate of the VFO oscillator tube to 150
volts instead of the 300 volts unregulated that the
"stock" DX-100 runs.  This requires the addition of a
dropping resistor, a 7-pin tube socket, and the 0A2
removed from the screen circuit.  Takes less than an
hour to accomplish and is a very simple modification
to make.  This modification also adds to the
improvement in stability of the DX-100 VFO when done
with the other two modifications.  You MUST replace
the screen regulator with an 0B2 when regulating the
plate to 150 volts.  

The same modifications work VERY well with the VF-1
except that the VFO really needs to be run from a
separate power supply (NOT the internal power supply
in the DX-35, DX-40, DX-60, or other transmitter) that
provides 6.3 VAC for the heater ("filament") and 150
volts regulated for the B+.

Glen, K9STH

--- Bob Peters <rwpeters at SWBELL.NET> wrote:

Hi All and happy Turkey Day. I am on the wants for an
external VFO for my DX100.. Not a VF-1... I want an
Eico, Hali, or Globe powered VFO. I don't want a
basket case but want a working clean one. Gotta be one
out there...

Glen, K9STH

Website:  http://k9sth.com

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