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You know that BF247x is identical to BF246x with only different pin assignment? So it can be used as replacement. Also B and C types have overlapping parameter ranges, a selected B type might work without circuit modifications.
Nevertheless all these FET types are obsolete with only remainders availables from some catalog distributors and DIY shops. There's no one-to-one replacement. Use the best fitting high Idss VHF FET available at your site (e.g. popular types like J310/U310), modifying the circuit parameters as needed.
Most of the low frequency designs (<100MHz) allow to put two identical JFETs in parallel (pin to pin), doubling in this way the total IDSS.
For example placing two J310 in parallel you can get a maximum IDSS of about 120mA.
Most of the low frequency designs (<100MHz) allow to put two identical JFETs in parallel (pin to pin), doubling in this way the total IDSS.
For example placing two J310 in parallel you can get a maximum IDSS of about 120mA.
It is for this oscillator **broken link removed**
I have found that wothout any components changes it accepts crystals from about 450KHz to 25MHz. this is true for bf247c and bf246c (I tested it with the bf246c, after your last post).
With mpf102 and j310 it cannot go that high and the oscillator output is lower at the same set positions.
I have no idea if this wider oscillation frequency range has to do with the gain of the fet or not. I have tried different combinations for the gain loop caps and the two 150pf gave max oscillation range.
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