07-25-2008, 10:39 PM
Hi Dave - and welcome!
I would seriously consider changing the value of capacitor (151) to 4.7 uF, non-polarized. This should help the performance of the tweeters by lowering the crossover frequency to around 4000 cycles, permitting more of the midrange audio frequencies to be reproduced by the tweeters, as well as the high end.
This is detailed, as you know, on this page on my website:
ERROR in Philco Model 38-690 Tweeter Wiring
The tweeters should not be really loud in a 38-690 - they should be noticeable, but not overpowering. This is unlike the 37-690, the tweeters of which are really TOO loud.
As for the back cover. The use of a back should make the passive radiators operate more efficiently. However, the original back had ventilation holes all the way down - which was necessary, since most of the heat was generated by the lower chassis (audio amp and power supply). The unsealed back would thus, theoretically at least, defeat the purpose of the radiators. Nevertheless, I've owned such receivers in the past (wish I still had one now...long story), and when I listened closely to one of the radiators, I could always hear sound coming from it, even though the set had no back, or a ventilated back.
I would seriously consider changing the value of capacitor (151) to 4.7 uF, non-polarized. This should help the performance of the tweeters by lowering the crossover frequency to around 4000 cycles, permitting more of the midrange audio frequencies to be reproduced by the tweeters, as well as the high end.
This is detailed, as you know, on this page on my website:
ERROR in Philco Model 38-690 Tweeter Wiring
The tweeters should not be really loud in a 38-690 - they should be noticeable, but not overpowering. This is unlike the 37-690, the tweeters of which are really TOO loud.
As for the back cover. The use of a back should make the passive radiators operate more efficiently. However, the original back had ventilation holes all the way down - which was necessary, since most of the heat was generated by the lower chassis (audio amp and power supply). The unsealed back would thus, theoretically at least, defeat the purpose of the radiators. Nevertheless, I've owned such receivers in the past (wish I still had one now...long story), and when I listened closely to one of the radiators, I could always hear sound coming from it, even though the set had no back, or a ventilated back.
--
Ron Ramirez
Ferdinand IN
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