Mk-III - Chassis Parts

I finally got the chassis and panel mechanical parts fitted today:

 The plate choke lead eyelet has been moved.  The 20 Watt dropping resistor is the large resistor mounted in the lower left of the photo.  The 12 Watt resistor was originally intended to be under the chassis, and still will fit but I am concerned about a few clearances so I put it on topside for now, I don't think is looks too bad there?  The grommet on the left is for HT leads and the one on the right is for the keying side of the 12 W resistor and the meter leads. The eyelet on the far right is intended for the Crystal socket's leads and the OSC INDIC lamp leads, which may be passed though the grommet as well, depending on the space.

The sockets are in place.  I have #6 Screws with some homemade about 1/8" brass spacers on the porcelain 807 tube socket.  This is to give more clearance for the top grid cap connection of this rather large tube.  The 6V6 octal socket is also  temporally in place. It was originally intended to be riveted into the chassis.  The holes may now be too large to accept the rivets correctly, and on second thought I should have simply used  #4 flat head screws in order to pick up chassis ground,  The other #4 screws used for the solder tags were recessed and fit nicely into the chassis, they should provide good ground connections.

The wiring side layout turned out to be pretty clean.  Each circuit (the Oscillator and Power Amplifier) have adequate solder tags and grounding points, which should provide a good clean layout, both mechanically and RF wise,  for the remainder of the components and wiring harness. 

In this view looking to the front of the chassis shows the oscillator coilform in place.  I decided to try a toroidal core for this coil. It is non-period (not from ca. 1939) but the inductance is easy to control and it will produce a good stable coil with a well contained RF field.  I can always replace it with a standard cylindrical coil later if I ever want to. 

Looking to the rear the also non-period BNC RF connectors are in place, one is for antenna and the other for the receiver.  The 1/4" key jack is on the far right. The large power connector is a 4-pin Cinch connector.

It took a while to locate this connector.  I originally intended to house the 20-Watt dropping resistor in the external power supply and run both the HT supplies  (620V HT for the Power Amp and 230V Oscillator supply HT-LOW) to this chassis. 

Note:  I also used the male or plug version (series 304-P) of this connector as a saftey feature.

From the front, the openings for the panel controls can be seen.

The tubes and coil plugs are shown ~ test fitted!  The solder tag in the front center will be where the front panel's shield connects to the chassis ground. 

Here is the almost complete front panel and the chassis.  The 5" x 7" compact size of this unit was one of the reasons I wanted to build this transmitter.  Also note they are sitting on top of the companion receiver; The 1935 Black Chassis HRO! 

The front panel with the crystal holder and OSC INDIC bulb in place.  The controls are not mounted yet as they pass though both the chassis and panel so they are mounted last, as you can see by the marks around the holes, they have been test fitted to the chassis before. 

Also, HRO style knobs still need to be located but these knobs from BC-610 TUs are the exact same size.

The tin shield is shown now in place.  This shield is actually made from 20AWG steel plate, it is intended to be grounded to the chassis. A "safely circuit" capacitor will be required to isolate the high voltage DC from these capacitors.

 Also shown is my home build crystal socket.  It is the same design I used on my Paraset so the crystals are also interchangeable...