21-07-2020, 06:46 PM
I replaced one Silver Mica (label is 106 pF or something). It measured 85 approximately. After padding with a ceramic disc I had less! Took disc off and capacitance had dropped to 64 pF!
One cap is 196pf and labelled 200PF, so it went back in. The other three had ceramic disc caps put across the backs.
All of coil / switch pack reconnected.
First IFT remounted and wired in except for AGC resistor.
Second IFT (the one with new winding on detector) is mounted, but not connected.
I cut grass today, so might go at it fresh tomorrow. I'm optimistic. The RF tuner seems OK and the LO tuner now only shorting at one spot. It's 500 pF + 250 pF approximately, all the similar size ones I have are 500 pF + 500 pF, and I'm not going to rip half the vanes out! I'll try some ultra fine sandpaper on card to correct width.
It's been interesting reverse engineering it and figuring out why they did some things. I'm delighted it was relatively easy to wind the IFT. I do have a project in mind to make 1.7 MHz IFTs. The current version of the ZN414 / MK484 from China works to 2 MHz. So half way between 160m Amateur band and end of European MW (US maybe extends to 1.7 MHz, but I'm not planning on visiting).
One cap is 196pf and labelled 200PF, so it went back in. The other three had ceramic disc caps put across the backs.
All of coil / switch pack reconnected.
First IFT remounted and wired in except for AGC resistor.
Second IFT (the one with new winding on detector) is mounted, but not connected.
I cut grass today, so might go at it fresh tomorrow. I'm optimistic. The RF tuner seems OK and the LO tuner now only shorting at one spot. It's 500 pF + 250 pF approximately, all the similar size ones I have are 500 pF + 500 pF, and I'm not going to rip half the vanes out! I'll try some ultra fine sandpaper on card to correct width.
It's been interesting reverse engineering it and figuring out why they did some things. I'm delighted it was relatively easy to wind the IFT. I do have a project in mind to make 1.7 MHz IFTs. The current version of the ZN414 / MK484 from China works to 2 MHz. So half way between 160m Amateur band and end of European MW (US maybe extends to 1.7 MHz, but I'm not planning on visiting).
