Hi:

Am in the process of replacing a broken Dynamic speaker. The size of the speaker is unusual (7") but I lucked out in finding another of similar size HOWEVER the field coil of the original is rated at 780 ohms and the replacement is 2,000 ohms. I did a test with the new speaker and it does sound good. Will this big difference in ohm value with the new speaker's field coil be an issue down the line? I know that replacment with a PM is also a posssiblilty but I would like to keep the set as original as possible. Thanks

Depends how the speaker field was wired into the radio. Most sets used the field as a filter inductor (part of a pi filter) in the B+ supply. So, a higher-value impedance speaker field wouldn't damage anything but could result in reduced set performance (due to lower B+ voltage from the higher voltage drop across the high-resistance field). Symptoms of low B+ voltage would be poor sensitivity, and possibly audio distortion at high volume levels.

If this is the case, you could shunt the speaker field with a power resistor to restore the original impedance. This may result in a little more residual hum but it probably won't be objectionable.

If the speaker was wired just as a load to ground off B+, you don't need to do anything since the difference in field resistances won't affect the B+ current very much. The speaker should work fine as is in that case.

Posting a make/model of the set in question would improve your chances of getting a useful answer.