Re: SX-117 AVC pumping
¿ªÔÆÌåÓýFloyd, ? I¡¯m curious as to the type of capacitor that was replaced.? Hallicrafters often used the Cornell Dubilier ¡°Tiny Chief¡± type in many of their products. ?These have a pink-0colored appearance with yellow stenciling.? They have a high failure rate today. ? Paul ? From: [email protected] <[email protected]> On Behalf Of Floyd - K8AC
Sent: Friday, August 9, 2024 9:23 AM To: [email protected] Subject: Re: [HallicraftersRadios] SX-117 AVC pumping ? Finally resolved the AVC pumping problem.? As I mentioned, AVC pumping by off-frequency signals occurred only with the selectivity switch in the 2.5 position.? So, looked for what's different with the selectivity switch in that position.? That switch, S4, has four sections that switch resistors into the ground leads of T6 and T8 (50 KHz IF transformers) and switch capacitors between the coupling networks of T5/T6 and T7/T8 and ground.? Those actions change the bandwidth of the 50 KHz IF.? I checked the value of the resistors and capacitors and none of them were close to the values shown on the schematic.? After replacing the 220 ohm resistors and the? .01 uF capacitors, I realigned the IF at 50.75 kHz.? The result is that the AVC pumping has been eliminated - strong signals outside the passband no longer desensitize the receiver.? ? ? 73, Floyd - K8AC |
Paul Christensen