SB-610 source follower.

[w1id]

As mentioned in one of my previous replies, I use a source follower in my SB-303 to monitor signals on the SB-610. Since it is a very simple circuit, it will be described in words. I use a Siliconix E300 FET but you any garden variety FET should work. The gate has a 100K resistor to ground. Coupling to the last IF is through a 5pF cap. The source has a 1K resistor to ground. Coupling from the source is through a 0.001uF cap. Power is supplied from the +15VDC source. Use at least a 0.1uF bypass cap on the drain. Also use a 100 Ohm resistor from the +15VDC souce to the drain for isolation. The key to preventing oscillation is to use the shortest leads possible. For example, the FET is mounted "dead bug style" and 1/10 watt resistors are used throughout. All connections to ground are directly on the PC board copper. The 0.1 uF drain bypass cap is a polyester type. From the 0.001uf cap, connect a length of miniature coax to one of the spare RCA jacks on the back of the receiver. I!
f need be, you can probably reduce the value of the gate resistor to some lower value such as maybe 50K. Be sure to retune the last IF transformer after adding the source follower. You should now be able to use any coax of any length to your SB-610 without affecting the receiver. I would like to reiterate that the display on the monitorscope is purely for esthetics due to the relatively narrow bandwidth of the crystal filters and AGC action. It looks pretty. I would like to add that I am set to retire my old SB-610. No, I'm not selling it or getting rid of it. Just giving it a rest. I built it from a kit in 1971. That's pretty good service! It will be replaced by a Tektronix 465 dual channel scope. Channel A will be used to monitor received signals while channel B will be used to monitor transmitted signals. Since this is a 100MHz scope, all that's needed is a small pickup loop inside my antenna switch. The 465 was cheap, only paid $125.00 at the local surplus store. Only prob!
lem is it has no handle. No problem really, I don't want or!
 need a handle.
w1id
e-mail: w1id at fcgnetworks.net

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