UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Aga Baltic AH37. Need help identifying old capacitor from 1930s radio

ms660 · 9th Oct 2018, 10:33 pm

Had a look at all the new photo's, so far my plot is the 1st RF transformer has a tapped antenna primary for the band change (bottom end of the primary connects to chassis at the 1st RF tuning capacitors earthing lug), top end of the primary connects to the antenna and the bottom end of the volume pot, the primaries tap is connected to a contact of one of the switches (there are two switches for this transformer) the other contact is connected to chassis via the same wire that connects the bottom end of the primary to the chassis.

The top end of the volume pot is connected via a resistor to the filtered HT supply and to the bottom end of the de-coupled cathode bias resistor for V1, when the volume control is at maximum its shunting effect across the antenna input will be at minimum and the output from the V1 will be at maximum, when the volume control is turned towards minimum the shunting effect across the antenna input will increase and the cathode bias voltage will increase and the output from V1 will decrease.

The secondary as expected is also tapped for band change and uses the other switch contacts in the same way as the switch for the primary, using the same common chassis connection wire.

The 2nd RF transformer appears to have an anode tuned primary that's tapped for band change, the secondary being an untapped winding connecting to the control grid of V2 with the usual grid leak arrangement for detection, can't help thinking that the control grid of V2 would have had some permanent bias on it, possibly from the original bias source for V3 or from the cathode circuit of V2.....

That's it for the mo, all subject to scrutiny/revision/abandonment of course.

Lawrence.

9th Oct 2018, 10:33 pm	#101
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Aga Baltic AH37. Need help identifying old capacitor from 1930s radio Had a look at all the new photo's, so far my plot is the 1st RF transformer has a tapped antenna primary for the band change (bottom end of the primary connects to chassis at the 1st RF tuning capacitors earthing lug), top end of the primary connects to the antenna and the bottom end of the volume pot, the primaries tap is connected to a contact of one of the switches (there are two switches for this transformer) the other contact is connected to chassis via the same wire that connects the bottom end of the primary to the chassis. The top end of the volume pot is connected via a resistor to the filtered HT supply and to the bottom end of the de-coupled cathode bias resistor for V1, when the volume control is at maximum its shunting effect across the antenna input will be at minimum and the output from the V1 will be at maximum, when the volume control is turned towards minimum the shunting effect across the antenna input will increase and the cathode bias voltage will increase and the output from V1 will decrease. The secondary as expected is also tapped for band change and uses the other switch contacts in the same way as the switch for the primary, using the same common chassis connection wire. The 2nd RF transformer appears to have an anode tuned primary that's tapped for band change, the secondary being an untapped winding connecting to the control grid of V2 with the usual grid leak arrangement for detection, can't help thinking that the control grid of V2 would have had some permanent bias on it, possibly from the original bias source for V3 or from the cathode circuit of V2..... That's it for the mo, all subject to scrutiny/revision/abandonment of course. Lawrence.