Apex Microdyne Super

The Apex Microdyne Superheterodyne from 1925 is an 8-tube battery powered super that was sold as a kit. It has a stenciled panel. All of the transformers are labeled Apex and are comprised of 2 IFs, 1 IF filter, and 2 audio interstage transformers.

There have been a few of these for sale lately and a few more in collections on the net. After examination of the pictures there is one thing that is notable in that every radio is very similar. This is a departure from the typical kit-build that usually incorporates parts and wiring added by the builder. This leads me to believe that either a complete kit that was mostly pre-assembled was being sold or that the radios were completely assembled prior to delivery to the customer.

The ad above is from Radio Digest of Aug 26, 1925. Note the price of $97.50.

As found above. Or rather, fresh out of the box.

The second audio interstage was open. It had leaked quite a bit of the potting material - bee's wax - all over the place. The other transformers had leaked a bit of wax as well. Since the parts of the transformer housing are held together with 2 pins  the seal is poor enough to allow leakage especially if the radio is stored in a warm environment. Cleaning off all of the hardened, sticky wax was the biggest task in restoring the chassis - well - and fixing the open 2nd audio - below.

The buss wiring on all of these kits is very similar. One reason to believe this was built by a radio shop is the remains of a shop claim tag, torn into chunks and used as an insulator/spacer to prevent shorts - Above.

This really wasn't necessary unless the chassis was going to be handled roughly. Possibly in shipping? Which would also lead one to believe that this was a pre-delivery addition by the builder.

Soldering joints, though corroded, are good and no buss wire broke free in transit.

2nd audio interstage taken apart showing potting material - wax.

With the wax removed the transformer is loose. Since it is so similar and not visible I just inserted a standard (156) replacement and wired it up.

The power is wired through a 7 conductor plug (center rear). The 2 black wires connect to a ~4.5V C battery which was located on the chassis.

Even though the cabinet looked pretty good, it was made of mostly solid walnut and the finish was mostly gone leading to warping (the issue with "solid" wood). Sine the panels were several boards that had been joined the warping had split the joints apart as well as twisting them somewhat.

The only way to make it right was to not only bust the cabinet apart but to also break apart the panels and rejoin the individual pieces after making minor cuts to remove the stress that broke the glue joints. Note the lighter new piece grafted to the rt. side panel. This piece was missing. (center right)

Never enough clamps - or hands.

Ta-Da. Sue holds reassembled cabinet less lid.

The finish is med. walnut DYE (not toner) topped with several coats of clear shellac.

This radio does not have an antenna coil like the Victoreen (previous post) so it needs a loop antenna. My test loop is shown above.

Above is a video with the radio in use.

A couple of notes:
Hand capacitance is an issue in tuning. The tuning caps could use some more shielding. The big, brass dial of the Apex vernier is electrically connected to the rotor so it probably makes this worse than when a plastic dial (knob) is used.
The little switch (knob) on the lower left enables the user to select either one or both stages of audio amplification - using 6 tubes or 7 tubes total.  Using the 2nd audio while tuning has some advantages and tone is better (this may be somewhat related to the new audio trans installed in the interstage), But the audio level is adequate using only the first audio stage.
When the radio is "tuned" for the most conservative use of the batteries = lowest A voltage, the oscillator can stop. Turning up the A voltage will prevent this but run the tube filaments hotter.