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Title: HQ-180A - V16 Cathode Capacitor Question Post by: KW4H on January 03, 2022, 01:34:07 PM V16 is the 6AQ5 "Power Output" tube in the HQ-180A. The cathode of this tube has a 430 ohm resistor and a capacitor to ground. Some drawings indicate that this capacitor is C82D -- a 40uF section of the main filter capacitor can. Other drawings show this capacitor as a 25uF/25v electrolytic. In front of me I have two HQ-180A's. One of them has the 25uF/25v electrolytic installed, the other has only the resistor and no capacitor at all. Both HQ-180A's have the three-section main filter capacitor -- there is no section "D".
So, what's correct? Should there be a capacitor on the cathode of V16 to ground, or did Hammarlund eliminate that in a later version of the radio? I'm not able to find a schematic that doesn't show this capacitor, but there are so many different manuals and versions out there I really can't be sure. 73, Steve - KW4H Title: Re: HQ-180A - V16 Cathode Capacitor Question Post by: DMOD on January 04, 2022, 12:25:19 PM V16 is the 6AQ5 "Power Output" tube in the HQ-180A. The cathode of this tube has a 430 ohm resistor and a capacitor to ground. Some drawings indicate that this capacitor is C82D -- a 40uF section of the main filter capacitor can. Other drawings show this capacitor as a 25uF/25v electrolytic. In front of me I have two HQ-180A's. One of them has the 25uF/25v electrolytic installed, the other has only the resistor and no capacitor at all. Both HQ-180A's have the three-section main filter capacitor -- there is no section "D". So, what's correct? Should there be a capacitor on the cathode of V16 to ground, or did Hammarlund eliminate that in a later version of the radio? I'm not able to find a schematic that doesn't show this capacitor, but there are so many different manuals and versions out there I really can't be sure. 73, Steve - KW4H Could you have meant V17? I usually replace the 430 ohm cathode resistor with a 470 ohm 1W and the capacitor with a 47 uF 50V electrolytic. It is there to prevent negative feedback and stabilize the bias. Phil - AC0OB Title: Re: HQ-180A - V16 Cathode Capacitor Question Post by: KW4H on January 04, 2022, 09:50:15 PM Could you have meant V17? I usually replace the 430 ohm cathode resistor with a 470 ohm 1W and the capacitor with a 47 uF 50V electrolytic. It is there to prevent negative feedback and stabilize the bias. Phil - AC0OB Thanks for the reply, Phil. The 6AQ5 is V16 in my HQ-180A. I will absolutely replace that resistor and capacitor as you suggested. 73 - Steve, KW4H |