06-12-2006, 06:53 PM
This is an "early series" Model 70....and this one has baffled me for quite a while.
Sensitivity drops off a lot below about 750 Khz, but is fine above that.
Besides a total chassis overhaul (bath tub caps, electrolytics, bad wiring, etc), I also replaced the resistor and cap across the 600 Khz trimmer with a silver mica type and a good 5% carbon resistor...and that helped a bit. I also replaced the dial, and made sure it fit "on the mark" properly with the old one.
Also made sure the IF was properly aligned, and that the freq tracks across the dial...and it does within 10Khz of dial markings. Followed the rf/osc/ant alignment procedures to a "T".
Also removed the tuning condensers and re-mounted them with good grommets...I mean, I really went through this thing.
All coils check out fine. Resistances are just about where they should be.
All tubes check fine on a Hickock 539B.
Still, it's not up to par.
I'm grabbing at straws, now...
Antenna is a 20' run of wire across the ceiling, set is grounded to a cold water pipe.
Any suggestions greatly appreciated.
Sensitivity drops off a lot below about 750 Khz, but is fine above that.
Besides a total chassis overhaul (bath tub caps, electrolytics, bad wiring, etc), I also replaced the resistor and cap across the 600 Khz trimmer with a silver mica type and a good 5% carbon resistor...and that helped a bit. I also replaced the dial, and made sure it fit "on the mark" properly with the old one.
Also made sure the IF was properly aligned, and that the freq tracks across the dial...and it does within 10Khz of dial markings. Followed the rf/osc/ant alignment procedures to a "T".
Also removed the tuning condensers and re-mounted them with good grommets...I mean, I really went through this thing.
All coils check out fine. Resistances are just about where they should be.
All tubes check fine on a Hickock 539B.
Still, it's not up to par.
I'm grabbing at straws, now...
Antenna is a 20' run of wire across the ceiling, set is grounded to a cold water pipe.
Any suggestions greatly appreciated.
