February 28, 2011 at 8:24 pm #2265AnonymousInactive
I,m working on a Marconi 214 battery radio,which probably hasn’t been operating since the 50’s, when someone for some reason disconnected and butchered the band switch. I have managed to recap and replace needed resistors, works very well on BC, but the wiring to the SW bands were cut and am having trouble knowing which winding on the coil(L5) was used for feedback or tuning . I have tried it both ways and have oscillation but when we measured the inductance of the coil one winding seems to be slightly higher than the other. The way it is now, the frequency seems to about 3 megs too high on the high end of the band and drops out of oscillation before the bottom end of the band.The frequency cant be lowered any more by the trimmer (have tried L5 adjustment and C5).Not sure why it was butchered to start with but it was direct wired for BC only, so something may have been wrong with SW band. If reducing the value of the R2
will I be able to perk up the oscillator tube at the lower end of the SW band. Any info would be appreciated, thanks Martin………….
Download marconi214.jpg. (Caution: This file may not be virus scanned.)March 1, 2011 at 4:04 pm #2269AnonymousInactive
Thanks for your reply Gerry, The BC band is on its own switch wafer, I did try another tube but results were similar, you say the coil can only work one way , I guess my question is how would one visually tell which way it would have been connected, as all wiring was removed from it.The coil is wound of approximately #24 on one level. Would the lower microhenry coil be the feedback, with the higher being the tuned coil or opposite? The coils are not shorted together and with them being wound in parallel, I cant see there being a short in one coil.March 2, 2011 at 3:37 pm #2274AnonymousInactive
The switch had been completely disconnected, so I took it apart and checked it over cleaned and reassembled, rewired to the schematic best to what I thought was correct, so I know the BC is working well as I said previously, the only part I couldn’t be sure of was which way L5 had been connected. I may have to get a new 1A7 to try and see if it will oscillate at the low end, as neither tubes I have here will. Testing continues………………
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