EdThe attached circuit is for a JFET input transformer feedback amplifier with a relatively high input impedance at 10MHz along with relatively low noise and distortion.
A Minicircuits T9-1 should suffice for the transformer.The major limitation when using these transformeres is that dc magnetisation of the core causes distortion. A differential version using a transformer with centre tapped secondary and primary will be less sensitive to this in that only dc current mismatch in the 2 halves of each winding contributes to core magnetisation.
A negative supply is used to ensure the JFET is biased correctly.Other arrangements such as using a string of capacitively bypassed diodes (or a Vbe multiplier) in the source circuit are also possible. Its important for stability that the gain bandwidth of the FET is somewhat greater than the ft of the pnp transistor.
Bruce Ed Palmer wrote:
Bruce Griffiths wrote:...By compensating for the different output voltages of the 7474 vs. the 74HC74. Good point. Which means more hacking on a perfectly good circuit board. I hope I can leave this alone and duplicate John Ackermann's 'loose coupling' connection on the input of the 7474. It should be relatively easy to duplicate the circuit on a breadboard for testing.EdGiven that the divider load current, if one substitutes a 5V CMOS flipflop for the 7474, only increases to about 5mA pp, using a 74HC74 is probably prudent given the PCB layout used, in that it may avoid EMI issues that may be a problem with faster logic. However it may then be prudent to attenuate the output of the divide by 2 fliflop to avoid overdriving the following emitter coupled pair.Thanks for the ideas, Bruce. EdBruce Ed Palmer wrote:The schematic is available here: http://www.murgatroid.com/t_and_m/hp-00105-6100-figs.pdf . It's also available with circuit description & waveforms here: http://www.kennethkuhn.com/hpmuseum/scans/hp5065a_part3.pdf on pages 93-101 (pdf pages - not document pages). However, this copy doesn't show the schematic for the power supply board. I also see that document page 8-54 is missing which might be the problem.Ed Bruce Griffiths wrote:If you send me the schematic for the circuit in which its used I can answer that question better.Bruce Ed Palmer wrote:Perhaps, but given what it's replacing and what it's driving, is the difference significant?Ed Bruce Griffiths wrote:Ed Palmer wrote:Yes, I have the same configuration. The part number for the divider board is 05061-6165. The 10811 + daughter boards are used in the 105B, 5061B Cesium, and the 5065A Rubidium. The circuit loading problem is exactly the kind of issue I was expecting. Thanks for the warning. I could probably resolve it by replacing the existing 7474 with a 74HCT74, but I'd like to minimize the amount of hacking I inflict upon the unit.EdA 74AHCT74 would be a superior replacement. Bruce_______________________________________________ time-nuts mailing list -- time-nuts@febo.comTo unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nutsand follow the instructions there.
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