Eddy -
>>>>>>>>>>
I just re-read this, after I sent it, of course! Each R/C pair must provide a _60_ degree phase
shift for a total of 180 degrees in the network. The other 180 degrees comes from the tube itself.
<<<<<<<<<<
Yes, you can change the sidetone frequency that way. However, (there's always a 'however',) the
sidetone frequency is set to approximately the same frequency as the CO is offset for CW. This is
so if you set the incoming CW signal for approximately the same tone as the sidetone, your
transmitter will be close to the other station's frequency. The frequency is typically around
800-900 Hz, and a secondary problem is that it is more 'sawtooth' than 'sinusoidal'. There are a
couple of assumptions in this scheme that no longer necessarily hold true, but that's another 'however'.
This tone is ALSO used in the TUNE mode, the electronic equivalent of 'whistling into the
microphone', to produce a single tone SSB signal to tune up with. The lower edge of the filters in
the T-4X is not as steep as the later models, so moving down to 450 - 500 Hz _probably_ would be
ok. But obviously the tone generated must be within the passband of the LSB crystal filter.
The resistors and capacitors are selected to produce a 90 degree phase shift at the desired
frequency to set the tone that is generated. All Rs and Cs must be the same value. Someone made up
a chart of the values for each frequency, I'll see if I can find it. When you look at where those
components are located, you might be more interested in the following suggestions. :-)
I just set the receiver to ON, so that it stays on all the time, so I can hear my OWN signal. The
AVC does a terrific job of minimizing the loudness, which I help by just pushing the phones forward
rather than right over the ears. This works great, I know exactly where my transmitter is with
regard to the other signals, and am listening to a nice clean audio tone.
The other 'recommended' fix is to just use a keyer with it's own sidetone, and put the receiver in
STANDBY. You can either turn the SIDETONE control all the way down, or just don't connect the
cable, as long as you don't need VOX!
Another way would be to use the ~-60VDC level on the key in the UP position to turn off an external
audio oscillator that comes on when the key is DOWN.
If you use a straight key or bug, then do what we used to do and just listen to the transformer
hum!! :-)
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-B, C-Line&
TR-4/C Service Supplement CDs
<www.k4oah.com>
Edward Swynar wrote:
*/Hi Guys,/*
My poor old tinitus-rattled ears find the internal CW sidetone
oscillator frequency of the T-4X to be very fatiguing after
awhile...it's /too high/ in pitch for my liking in extended operating
sessions...
Has anyone ever /lowered/ the sidetone monitor frequency in their
T-4X...? Would any such change simply entail increased values of one
(or all) of the resistors R70, R71, & R72 (330K ohms stock each), as
well as increased capacitances for one (or all) of the
capacitors C129, C130, & C131 (180-pfd. stock each), at sidetone
oscillator V9a (12AX7A)...?
Many thanks for any & all feedback in this regard...
*/~73~ de Eddy VE3CUI - VE3XZ/*
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