[Norm_N_Tam]

I’ve heard that some early Philco superheterodyne radios used a dynatron oscillator with a 24 tube.  Apparently, only 24 tubes will work in these, and 24A tubes will not.  Does anyone know which models had this feature?  I’ve looked around at Philco schematics, and have yet to find one with a dynatron oscillator.

[Norm_N_Tam]

From the Antique Radios forum:

RCA certainly investigated and tested the dynatron oscillator circuit before the 24 tube was placed on the market; their senior tube engineers decided that the effect had too much variation from one tube to the next for them to support it as a recommended application.  Nevertheless, Crosley used it anyway.  When RCA fixed the problem in the 24A and discontinued the 24, a lot of Crosley owners were left high and dry.  Crosley sued, but RCA successfully argued that since they never supported dynatron operation of the 24 in the first place, they were not obligated to support it in the 24A.  Fortunately, in most cases it was just a matter of changing a resistor or two to get a 24A to oscillate in those radios.

Does anyone know which model Philco superheterodyne radios used a dynatron oscillator?  I'm interested to look at the schematics of such models.

Thank you!

[Ron Ramirez]

Norm_N_Tam

Welcome.

I have merged both of your posts into this thread.

Please read the Phorum Rules here:
https://philcoradio.com/phorum/showthread.php?tid=4586

The Rules do not allow multiple threads on the same subject.

Thanks.

[Ron Ramirez]

I see that the dynatron oscillator was used in the Crosley 122.

I do not recall ever seeing a similar circuit in a Philco.

Some Philco sets used an autodyne oscillator circuit, in which feedback is obtained from a cathode winding coupled to the plate winding of the oscillator coil. This differs from the dynatron circuit which is dependent upon negative resistance (secondary emission) in early tetrode tubes such as the 24 instead of feedback.

Some Philcos that come to mind using the autodyne circuit are models 70 (late), 51, 52, 90 (late), 71, 91, 89 and 19.

But these do not use dynatron oscillator circuits.

[Norm_N_Tam]

Thank you! I looked at that schematic before, but I mistakenly thought it was a TRF! They kind of hid the oscillator down near the bottom of the schematic....