[Drake] T4XC: where is C103 and it's friends?

[K6jek@aol.com]

Garey,

The carrier oscillator was the prime suspect.  Indeed it was 75 Hz low, 
enough for an audible difference.  I'm still not satisfied that I'm getting all 
that I ought to be getting through the 2.4 kHz filters.   I'll do audio sweeps in 
upper and lower sideband.  While I have it opened up and connected to the 
test equipment, I hope to run a few simple experiments, like paralleling those 
tiny coupling capacitors to see if it has any effect on the measurements.  But I 
have to find them first!

If I discover anything interesting, I'll post it.

Jon -

 From the schematic, I would expect to find C103 close to 
V1, since both ends are at that tube.

Before you start changing coupling caps, it would be a good 
idea to check the Carrier Oscillator setting.  Easiest check 
is to get someone to listen to you on the "other" sideband 
and see if perhaps the audio is "bassy" on that one. 
Generally speaking, 2.4 kHz is plenty wide enough for good 
communications audio, but is not Hi-Fi AM.  If your audio 
sounds "squeaky" on BOTH sidebands, you might want to try a 
different microphone if available.  Bottom line is, if your 
audio is too high pitched, (and assuming your voice isn't 
high pitched!,) it's likely an alignment or microphone problem.

73, Garey - K4OAH
Atlanta
 >>

In a message dated 3/29/04 8:30:06 AM, k4oah@mindspring.com writes:

<< 

K6jek@aol.com wrote:

> I'm having a devil of a time locating parts in my T4XC.  Is there a service 
> manual of some sort I can use to find things like C103 (.005 audio coupling 
> capacitor)?  Parts aren't labeled on the PC boards, the interconnects 
disappear 
> into serpentine bundles.  The colors have faded to beige.
> 
> BTW.  Has anyone improved the SSB audio on a T4XC?  K1JJ made the AM audio 
> terrific and documented the mods.  But the SSB audio, at least mine, sounds 
> squeakier than it needs to even allowing for a 2.4Khz filter.   The reason 
I'm 
> tracking down C103 and C113 and C108 is to see if opening them up a bit 
from .005 
> might open the T4XC SSB audio up just a touch at the low end.   
> 
> Jon, K6JEK