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Title: SX-99 QF-1 help Post by: N8IE on April 23, 2012, 12:38:06 PM Hello all,
Just acquired a Heathkit QF-1 to use on my Hallicrafters SX-99. From the QF-1 manual, I hook the coax connector to the plate side of the input IF transformer or the plate connection of the mixer tube at the socket. From looking at the schematic of the SX-99 it appears to be pin 8 of V3 (6SG7), the first IF Amp. Is this correct? I know I can get the filament voltage from the transformer, I need to ground one side to the chassis and the other I can tap off pin 7 of either V1,2,3 or 5. I need to find a good place to get B+ (120V to 300V). Any recommendations for this? Thanks in advance. 73 de N8IE Dan Title: Re: SX-99 QF-1 help Post by: KA2DZT on April 24, 2012, 04:31:52 AM QF-1 was one of the first kits I ever built some 50+ years ago. Damn thing didn't work right. Checking over everything I discovered that one of the filament pins wasn't soldered. After that fix it worked very well. I sold it years later. Probably about 25-30 years ago I bought another one at a fester. Damn thing didn't work right. Me being one of the smartest people on the planet, I quickly checked the filament pins. Sure enough the same pin wasn't soldered.
Best I can figure is that there was an error in the assembly manual which never said to solder that one pin. As I remember it is easy to hook up. Just connect your filament line to any 6.3v filament pin of one of the tubes in the receiver. You need to connect the B+, again find a B+ source point and then you need a ground line. The RF line gets connected to the plate of the first IF tube. Not exactly sure about the SX-99 but it sounds like you're on the right path. Follow the manual and I'm sure you'll get it hooked up right. Fred Title: Re: SX-99 QF-1 help Post by: N8IE on April 24, 2012, 07:18:05 AM Hello Fred et all. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
I was on the right track. :D The RG-58 cable does indeed connect to pin 8 of V3, this is the plate of the 1st IF amp. The 6.3VAC filament was a no brainer, I tapped it off V2. As for the B+, I found 205VDC on the HV supply. I replaced the 12AX7 with a new one, and did the normal smoke test, all the smoke remained inside their respective components. The QF-1 is a very nice addition to the SX-99. All that's left to complete my vintage Novice station is to make a circuit for the DowKey and rec muting. ;D 73 Dan, N8IE |