UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - R209

G6Tanuki · 17th Nov 2017, 4:43 pm

The R209 is a bit strange: there's no AGC operating on CW; instead a squidge of the BFO's output is tapped off, fed to the diode in the 1S5 BFO-valve and rectified - this then provides the negative bias-voltage to feed [via the second gang of the 'gain' control] to the grids of the RF/IF amps to provide manual gain control.

If you have what sounds to me like low BFO-injection and gain-control issues I'd check the BFO valve, as if this isn't producing enough output you'll lack BFO injection as well as adequate bias.

Another thing to check: the R209s of my acquaintance make use of some strange decoupling capacitors with a grey rubbery outer-jacket. These are replace-on-sight, in the same spirit as Hunts and Waxies. Leakage here can cause significant issues.

17th Nov 2017, 4:43 pm	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: R209 - BFO injection The R209 is a bit strange: there's no AGC operating on CW; instead a squidge of the BFO's output is tapped off, fed to the diode in the 1S5 BFO-valve and rectified - this then provides the negative bias-voltage to feed [via the second gang of the 'gain' control] to the grids of the RF/IF amps to provide manual gain control. If you have what sounds to me like low BFO-injection and gain-control issues I'd check the BFO valve, as if this isn't producing enough output you'll lack BFO injection as well as adequate bias. Another thing to check: the R209s of my acquaintance make use of some strange decoupling capacitors with a grey rubbery outer-jacket. These are replace-on-sight, in the same spirit as Hunts and Waxies. Leakage here can cause significant issues.