16-06-2020, 10:40 AM
(This post was last modified: 16-06-2020, 10:41 AM by Mike Watterson.)
I can't tell what sort of wire the side coil is. I don't think it's litz, but just very fine grey cotton covered. It's 4.3 Ohms (approx) and 1.75mH, so LW, solenoid wound, not wave wound.
Rear panel: light tinned copper with two layers of cotton (black outer) giving about 1mm spacing. 20 turns and inductance of 0.22mH, resistance approximately 1.2 Ohms. So regular black pvc solid hookup wire maybe 22 swg would be fine. Obviously the MW loop.
The external aerial loop is ONE turn of similar weight enamelled wire underneath. The outer loop was loose enough at the top to be 100% sure.
The P8 valve bases are all held on with two screws/bolts.
I unsoldered both wires on MW loop and one on the LW loop to measure and also to get an idea of the RF tuning cap (which goes to top cap and MW loop). I didn't disconnect LO cap.
RF cap goes from maybe 78 pf, inc trimmer(s), to about 505 pf. Possibly MW, not sure which position is MW & LW as the battery is in the Model A. Another difference with the "A" and possibly late comfort sets is the 1939 model has on/off on the volume control, but the model "A" has a three position switch, easier to leave on, so I unplug the AD3 pack when not in use. The 1939 model I have is "louder" than the A, perhaps the A has more worn valves, I'll check with valves from another octal battery set. Or maybe try the curve tracer. Maybe I even have some 1.4V octals. Note they should be 1.3V to 1.35V on a mains adaptor and HT 75V to 85V, the listed 1.5V and 90V are nominal fresh battery voltages. Decent valves will work down to between 1V and 1.1V (the Mixer/Osc stops first) and about 60V to 65V HT, though with reduced volume.
The two trimmers on the chassis are LW padding at 250kHz approx. The two trimmers on the tuning cap are for MW about 200m (1500kHz), though some sets are better aligned at 225m (1300kHz approx). Adjust the LO coil at about 600 kHz. Repeat the trimmers. If it's night and R.Ulster can be received, it's 1341 kHz, which is fine to align the padders.
Then adjust the two LW trimmers on the chassis (RTE @ 252 KHz is good if you can get it).
Maybe you have a signal generator? It can be fed at a low level to the A E one turn loop.
Align with the back in place and something of an equivalent to the battery pack as it affects the HF end of the MW RF tuning!
The coil inductances and capacitors are about what I'd expect.
Rear panel: light tinned copper with two layers of cotton (black outer) giving about 1mm spacing. 20 turns and inductance of 0.22mH, resistance approximately 1.2 Ohms. So regular black pvc solid hookup wire maybe 22 swg would be fine. Obviously the MW loop.
The external aerial loop is ONE turn of similar weight enamelled wire underneath. The outer loop was loose enough at the top to be 100% sure.
The P8 valve bases are all held on with two screws/bolts.
I unsoldered both wires on MW loop and one on the LW loop to measure and also to get an idea of the RF tuning cap (which goes to top cap and MW loop). I didn't disconnect LO cap.
RF cap goes from maybe 78 pf, inc trimmer(s), to about 505 pf. Possibly MW, not sure which position is MW & LW as the battery is in the Model A. Another difference with the "A" and possibly late comfort sets is the 1939 model has on/off on the volume control, but the model "A" has a three position switch, easier to leave on, so I unplug the AD3 pack when not in use. The 1939 model I have is "louder" than the A, perhaps the A has more worn valves, I'll check with valves from another octal battery set. Or maybe try the curve tracer. Maybe I even have some 1.4V octals. Note they should be 1.3V to 1.35V on a mains adaptor and HT 75V to 85V, the listed 1.5V and 90V are nominal fresh battery voltages. Decent valves will work down to between 1V and 1.1V (the Mixer/Osc stops first) and about 60V to 65V HT, though with reduced volume.
The two trimmers on the chassis are LW padding at 250kHz approx. The two trimmers on the tuning cap are for MW about 200m (1500kHz), though some sets are better aligned at 225m (1300kHz approx). Adjust the LO coil at about 600 kHz. Repeat the trimmers. If it's night and R.Ulster can be received, it's 1341 kHz, which is fine to align the padders.
Then adjust the two LW trimmers on the chassis (RTE @ 252 KHz is good if you can get it).
Maybe you have a signal generator? It can be fed at a low level to the A E one turn loop.
Align with the back in place and something of an equivalent to the battery pack as it affects the HF end of the MW RF tuning!
The coil inductances and capacitors are about what I'd expect.
