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Old 9th Oct 2019, 12:36 pm   #25
Christoffrad
Hexode
 
Join Date: Jun 2018
Location: Cambridge, Cambridgeshire, UK.
Posts: 260
Default Re: Ferrite rod antenna and RF amp for Valve radios

Hi Paul
I have checked continuity of all 4 windings ie the 2 LW and 2 MW.
I have measured the inductances of the LW and MW primaries 5mH and 530uH respectively and am using a air spaced capacitor that goes 30 - 350pf via a change over switch for the two sets of coils.

The hot end of the MW primary is clear to see so cold end is grounded. On MW it is not clear which is intended to be the hot end of the primary but I have made the assumption that as the LW hot is a red wire then of the two primary MW wires the red one is likely to also be the hot end. so each red goes via the c/o switch to the tuning C. On the secondary side for coupling into the transistor (via the c/o switch) it is anyones guess how the polarity goes. so one side of each coil is again grounded and the other goes via the switch to the transistor. (see my earlier posting for the circuit (which now has 47R added in the emitter)
Chris
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