D-104

[ke7trp]

Carl. You got me thinking.  I got a couple old DEMCO modulators. These take a D104 input and where designed for use with a D104. They then have and audio output.  I will have to open one to see whats inside. I seem to remember a a couple preamp tubes. It was just a simple Tube preamp with a limiter.   That might be interesting to test out into some of my ham transmitters. 

C

Its pretty hard to get beyond a 4.7 meg grid resistor without instability in a typical factory ham rig without a bit to a lot of extra work.

IMO its often better to terminate the D-104 externally in a real preamp and then drive the rig at the correct level.

[NR5P]

When I fixed my d104 element I had two problems.  The crystal was loose inside the element, the diaphragm was dented terribly, and the glue was hanging on in only a few places around the diaphragm. I used a razor knife and carefully cut where the glue was still hanging on.  I used a bic lighter and held the element upside down while holding the lighter just enough to melt the wax from the "rod".  Then I used epoxy on the bottom of the crystal and epoxy around the diaphragm.  I melted the wax back on the "rod" with the lighter.  I don't think the element could sound much better after repair. 

[ke7trp]

Thanks for the tip. I have a drawer of bad elements.. I will try this in my spare time.

C