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HQ-180A - V16 Cathode Capacitor Question




 
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Author Topic: HQ-180A - V16 Cathode Capacitor Question  (Read 196 times)
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KW4H
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« 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
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« Reply #1 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
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KW4H
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« Reply #2 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
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