My old Crosley model 26 has a switch for local stations, was this to prevent overloading the front-end? When I flick it to local, I get no reception at all.

Exactly. Early receivers did not have very good AVC (often called AGC now) circuits so strong local stations would overdrive not only the front-end but mixer and IF into distortion and intermod. You still see such switches on some car radios and scanners. And communications receivers have the equivalent in the way of a "RF-Gain" control. This switch was also handy if you just wanted to hear the locals without being bothered by weak unstable skip stations.

The fact that you hear nothing in the "local" position suggest that the over-all sensitivity is down for some reason.

-Nat

:My old Crosley model 26 has a switch for local stations, was this to prevent overloading the front-end? When I flick it to local, I get no reception at all.

Nat

The schematic indicates that the wire leading from the antenna terminal to the local-distance switch is wrapped around the wire that leads from the switch to the input coil. This wire acts as a capacitor when the switch is in the "local" position. If these wires aren't wrapped around each other, the radio will only work in the "distant" position.

You can duplicate this effect by connecting a 220 pf capacitor from the antenna input to the coil input.

: Exactly. Early receivers did not have very good AVC (often called AGC now) circuits so strong local stations would overdrive not only the front-end but mixer and IF into distortion and intermod. You still see such switches on some car radios and scanners. And communications receivers have the equivalent in the way of a "RF-Gain" control. This switch was also handy if you just wanted to hear the locals without being bothered by weak unstable skip stations.
:
: The fact that you hear nothing in the "local" position suggest that the over-all sensitivity is down for some reason.
:
:-Nat
:
::My old Crosley model 26 has a switch for local stations, was this to prevent overloading the front-end? When I flick it to local, I get no reception at all.

By the early 1930s, the automatic volume control system had been refined to a very accurate circuit. The automatic volume control circuit used in the best 1930s AM radios is still used to this day. It is able to reduce very strong local stations to a handlable signal, and able to increase the gain to incredible levels where you are able to selectively pick up stations across the country at a very listenable volume, even in radios with only one IF stage. I have found more radios of the 1930s-40s era that could pull in distant stations than modern radios. This includes lack of static interferance....well, many radios lacked static. Not all. The Zenith portables of the early forties amaze me in that what they say in their advertisements is true. I can operate a Zenith portable in a steel building with fluorescent lighting, and pick up static free stations in the center of the building. Turn on any modern AM radio, and there is nothing but buzz. Of course there were some radios of then that were of very poor quality. Most radios that I have come across that had the local/distant switch pretty much cut out most reception if put in the local position. If you take any radio, modern or old, and place it less than a mile away from a transmitter, it is likely to distort. If you live more than 4 or 5 miles away from a station and your radio distorts, you likely have a leaky AVC condenser or an open AVC resistor, or if it is the refined circuit, a defective diode tube and/or other components yet to be mentioned (there were many intricate and very clever refinements of the circuit). The only time you'd ever need to use the local/distant switch is if you lived very close to a transmitter. When you live very close, you need something that will cut the sensitivity of the receiver down really low. Assuming your radio uses the superheterodyne circuit, if you have all of your IF transformers adjusted very accurately, and your antenna trimmer adjusted accurately, your radio will have optimum sensitivity. Adjust IF transformers with a signal generator set as weak as possible, yet still audible. When you peak the antenna trimmer, you must use a signal generator setting that is extremely low and weak. After that, you want to find two very distant stations (best done at night) that are around that frequency. Listen to see if you can tune between the two and pick each one out separately, or if they overlap eachother (they may overlap even if everything is done right if their frequency is the same....listen for frequency calling). Carefully readjust the trimmer until maximum selectivity between the two is achieved. Very carefully touch up on the IF transformers by adjusting them only a hare's breath one way or the other and listen to see if this improves selectivity. Don't completely readjust the transformers while listening to the radio. You may throw everything out of sync. It is best to get the mean frequency set with a signal generator. Now, with all circuits adjusted as accurately as possible, if your tubes are in fair condition, and none of your condensers are leaky, your radio will be extremely sensitive. If you examine your distant/local circuit and find no shorts, put the switch to the local position. If all reception cuts out, it is likely working as it should. Take your signal generator and inject the strongest signal possible. You should be able to receive this signal even with the switch in the local position. This switch is only for really close "problem" stations. Noone would buy a radio that had to be switched from local to distant every time they changed stations. Keep that in mind whenever you have a radio problem. Radios were very close to perfect by about 1940 or so. The better models of that period should amaze you when you operate them, not leave something to be desired. The local/distant switch was a luxury item, and was usually found only on the best radios. AM was the medium of the time, and manufacturers spent a lot more time perfecting it back then than now. Now there is not much on AM worth listening to in most cities, and manufacturers focus more on FM.