Station AJ8MH - Marquette, Michigan

1937 Hallicrafters SX-16 Super Skyrider





Upper photos: 2 views of the under-side after replacing a few parts.  Right photo: The front panel after a good cleaning, some sanding and painting.  You wouldn't know it, but this panel had some serious corrosion.  I was lucky.  The panel turned out great.
 
The radio was purchased at a Hamfest in Dallas the summer of 2004.  A couple capacitors had been change along with the output transformer, and the radio looked as if some troubleshooting had been done.  However, the radio was never completed.  I made some basic resistance checks of the power and IF transformers plus the filter choke.  Convinced that these were OK, I cleaned the radio then proceeded to change caps and a few resistors.

I don't usually turn on acquired radios until all components have been either changed or checked, and this was no exception.
 
Since I had a warning about the wax dipped power transformer failing, because of age and heat in this old radio, I decided to slowly bring it back to life.  I often read about placing a 40 watt lamp in series with the AC power lead, so I built a little box that would allow me to do just that.  I added a switch to short-out the lamp when I wanted full AC applied to the radio.
 
I also heard that it's a good idea to bring up the radio without the rectifier tube installed, but with all the other tubes plugged in.  I guess the idea is to test the high current filament section of the transformer and the tubes, before applying high voltage.
 
After allowing the radio to burn-in for a couple hours, I turned it off, installed the rectifier, and once again, applied power.  A quick check of some key voltages proved good, so I started with the 465 kHz IF alignment.
 
The transformers tuned as expected, including both wide and narrow selectivity settings.  Now it was time for the RF alignment.
 
This is when I found sensitivity to be terrible.  I changed the 6K7 RF amplifier and the 6L7 mixer, but no improvement.  After disconnecting the signal generator cable from the antenna input, and moving it near the coils between the RF amp and the mixer, I noticed an increase in signal level.  I turned the band switch to the next band and back, and heard the sensitivity increase for a second then fall back off.
 
I already cleaned all of the band switch contacts.  Thinking that I may have a serious contact issue, I started to poke around the wafer at the input to the mixer.

The signal would increase and decrease with each poke, so I made some resistance checks, which revealed an open between the back and front of the individual wafer (part that rotates) effectively opening the path to the 6L7 grid.
 
To repair the open, I soldered a small strand of wire between a metal sliver, sticking through the wafer from the back, to the metal rotating contact on the front.  Without completely disassembling the wafer, I have no idea how the front and back were originally connected.
 
The alignment continued without any additional problems.
 
I took the radio off the workbench, and moved it the the radio room.  After connecting an antenna, I sat amazed for the next 2 hours listening to the radio perform.  The amount of progress made in 10 years between my RCA Radiola 17 and this radio is unbelievable.
 
Sensitivity isn't the greatest on bands 5 and 6, but it's more than adequate on the lower bands.  I think the FCC had the right idea asking Hallicrafters to add some additional amplification to the radio to support their needs.  This radio was manufactured as the SX-17.
 
The speaker to the right isn't some Hallicrafters prototype. It's my poor attempt at garage woodworking.  Hey, it sounds pretty good, and it's a lot cheaper than an original R-8T speaker!

Hallicrafters SX-16 Super Skyrider (Manufactured in 1937)

Coverage:  550kHz to 61mHz in 6 bands
 
11 Tubes:  6K7 RF Amp - 6L7 Mixer - 6J5G Osc - 6K7 IF Amp 1 - 6K7 IF Amp 2 - 6R7G 2nd Det AVC - 6V6G 1st Audio Output - 6V6G Output - 6J7 Beat Osc - 6J7G Sig (Meter) Amp - 5Z3 Rectifier
 
IF:  465kHz

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