[EMAIL PROTECTED] wrote:
In a message dated 2/6/03 7:25:39 PM, [EMAIL PROTECTED] writes:
Just put a resistor in the plate of the
audio driver tube, in place of the transformer primary. I think around
10k 2 watt will work ok. Then couple the plate of the driver to the grid
of one of the 1625s with a capacitor. Leave the secondary of the driver
transformer hooked to both grids and bias as it was.
It will work as an auto transformer to couple audio into both tubes.
Works fine! Although gain will be somewhat less than with the transformer.
I've done this too with FB results as long as one is not trying to push any
power into the next stage, but only providing a voltage swing. Never had a
DX-100 so have to ask, in just what class are the 1625 modulator tubes
operating i.e., AB1 or AB2? If AB1 the scheme under discussion (or a phase
inverter, or an itty-bitty transformer) should work FB. Nada if AB2.
Dennis D. W7QHO
Glendale, CA
Hi Dennis,
The 1625s in the DX100 do go into AB2 to get full modulation. Thus the
driver transformer used is a step down transformer. 3:1 I think.
Using the resistor in the plate of the driver rather than the primary of
the transformer only allows AB1 operation of the modulators as you say.
You can not get full audio with that setup unless you reduce the power
on the finals enough to deal with less audio power.
1625s put out considerable more power in AB2 than in AB1. Unlike a 6146,
which will put out almost as much power in AB1 as it will in AB2.
73
Gary K4FMX
