02-21-2006, 03:51 PM
I had a 38-690 for 40 yrs until I sold it a couple of months ago. $1432!!!
Not many suggestions but yes, you must have good 5X4's plugged into your transformers. They supply the high voltage to the the entire radio. A check for the proper B+ on the audio output amp plates is sufficient at this point to verify that the rectifiers are doing their job. (50% on the tester is pretty crappy but it still should work).
As for the tweeters, look at the pins that insert into them; there are two thick and two thin ones- audio and field current. The "sockets" are mated for these two sizes but they can be forced in backwards yielding no audio. The tweeters are NOT loud so don't look for ear-splitting sound from them.
There is also a modification on phasing these tweeters- don't do that mod until you can hear audio. Better yet, don't attempt it.
For the time being, don't put your interstage power cable trough the cabinet hole- it will just chafe. Also, use some spray switch cleaner/lube on the 10 (?) pin power connector; you will be inserting/removing it many times so save wear on the irrepaceable connector.
Just things learned from the 38-690.....
Not many suggestions but yes, you must have good 5X4's plugged into your transformers. They supply the high voltage to the the entire radio. A check for the proper B+ on the audio output amp plates is sufficient at this point to verify that the rectifiers are doing their job. (50% on the tester is pretty crappy but it still should work).
As for the tweeters, look at the pins that insert into them; there are two thick and two thin ones- audio and field current. The "sockets" are mated for these two sizes but they can be forced in backwards yielding no audio. The tweeters are NOT loud so don't look for ear-splitting sound from them.
There is also a modification on phasing these tweeters- don't do that mod until you can hear audio. Better yet, don't attempt it.
For the time being, don't put your interstage power cable trough the cabinet hole- it will just chafe. Also, use some spray switch cleaner/lube on the 10 (?) pin power connector; you will be inserting/removing it many times so save wear on the irrepaceable connector.
Just things learned from the 38-690.....
Pete AI2V
