UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Lafayette Model HA-600A VERY DEAF

G6Tanuki · 28th Apr 2021, 8:37 pm

If by the "dotted line" you mean the one between RV1 and RV2, this indicates that the two controls are ganged.

RV1 is an attenuator on the antenna-input; RV2 alters the DC bias fed from the AGC-amplifiier TR12 to the front-end transistors.

The control-knob is probably marked "RF Gain" or "Attenuator" on the front-panel. This variable-resistor-in-the-antenna-input may seem odd but it was a common thing in first/second-generation solid-state receivers, which handled really-strong signals rather poorly. The last thing you wanted [in the US at least] on Medium Wave/AM broadcast-band reception was lots of front-end gain when there was a broadcast station putting-out 10Kw a couple of blocks away; but equally when you were trying to listen to a weak ham-station on 28MHz you _needed_ that gain.

Even 'professional/military' solid-state receivers of the era incorporated aerial-attenuator networks as a way to address the poor dynamic-range/strong-signal-handling ability of first-generation transistor RF-amplifiers/mixers.

28th Apr 2021, 8:37 pm	#7
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: Lafayette Model HA-600A VERY DEAF If by the "dotted line" you mean the one between RV1 and RV2, this indicates that the two controls are ganged. RV1 is an attenuator on the antenna-input; RV2 alters the DC bias fed from the AGC-amplifiier TR12 to the front-end transistors. The control-knob is probably marked "RF Gain" or "Attenuator" on the front-panel. This variable-resistor-in-the-antenna-input may seem odd but it was a common thing in first/second-generation solid-state receivers, which handled really-strong signals rather poorly. The last thing you wanted [in the US at least] on Medium Wave/AM broadcast-band reception was lots of front-end gain when there was a broadcast station putting-out 10Kw a couple of blocks away; but equally when you were trying to listen to a weak ham-station on 28MHz you _needed_ that gain. Even 'professional/military' solid-state receivers of the era incorporated aerial-attenuator networks as a way to address the poor dynamic-range/strong-signal-handling ability of first-generation transistor RF-amplifiers/mixers.