07-26-2008, 09:20 AM
If you compare the schematics of the 37-690 and 38-690, you will see that the tweeters are driven by the output tubes in the 37-690, as is the woofer. This is the reason the tweeters are so loud in the 37 model. (Too loud, in my opinion; even taking the NRSC pre-emphasis curve into consideration.)
In the 38-690, the tweeters are driven by the DRIVER tube; there is a special winding in the audio interstage transformer just for the tweeter voice coils. For this reason, the tweeters are more subdued in the 38 model.
I think this was an attempt by Philco to give the tweeters just enough "presence" without being "in your face" on the high end, unlike their 37-690 model. Now, some of us do not hear the higher frequencies as well as others, so the 38-690 may seem as if its tweeters are not working, when in fact they may be working just fine (even with the phase correction I discuss on my site). Syl has pointed this out already.
I also agree with Syl when he says the tweeters in these models are more like midrange speakers. The set was not designed to reproduce audio above 10 kc, anyway.
In the 38-690, the tweeters are driven by the DRIVER tube; there is a special winding in the audio interstage transformer just for the tweeter voice coils. For this reason, the tweeters are more subdued in the 38 model.
I think this was an attempt by Philco to give the tweeters just enough "presence" without being "in your face" on the high end, unlike their 37-690 model. Now, some of us do not hear the higher frequencies as well as others, so the 38-690 may seem as if its tweeters are not working, when in fact they may be working just fine (even with the phase correction I discuss on my site). Syl has pointed this out already.
I also agree with Syl when he says the tweeters in these models are more like midrange speakers. The set was not designed to reproduce audio above 10 kc, anyway.
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Ron Ramirez
Ferdinand IN
