Gary, I'm not familiar with the VF-1 but I have an Eico model 722 VFO in which I've replaced the electrolytic capacitors. It has its own AC supply. I haven't tried to use it on the air yet so I can't say anything about how much it drifts. It should be possible to correct drifting by using capacitors with temperature coefficients that corrects for temperature drift of other components in the oscillator circuit. Old carbon composition resistors may be a problem as well. They tend to absorb moisture and increase in value. If you find any that are off in value, replace them with good RF quality film resistors.
The 722 also uses cathode keying. Rather than changing a cathode keyed VFO to grid block keying, my approach would be to use a sequential keyer that turns on the VFO, then keys the transmitter a couple of milliseconds later, then on key up turns off the transmitter first, and lastly turns off the VFO. That gets rid of chirps, and it eliminates key clicks as well if the rise and fall times of the stages following the VFO are controlled. I think shaped grid block keying works best for amplifiers rather than VFOs. If you try to start a VFO slowly, you could get a major chirp, or it might not start at all. In my view, control of rise and fall time is best done in the stages following the oscillator. If you do what Collins did in the 310B (I have one and it is a beautiful CW rig) and run the VFO at one half of the operating frequency (of the lowest band in the case of the 310B), you can leave it running and just key the following multiplier(s) and amplifier. That avoids the problem of a back wave from a constantly running VFO at the operating frequency. It would also avoid the problem of having to key both a negative and a positive line (I'm assuming your 2-NT uses grid block keying and that's why you are thinking of converting a VFO to that.) 73, Bob AD3K > -----Original Message----- > From: drakelist-boun...@zerobeat.net [mailto:drakelist- > boun...@zerobeat.net] On Behalf Of Gary Winkelman > Sent: Tuesday, January 05, 2010 9:26 AM > To: drakelist@zerobeat.net > Subject: [Drakelist] Drake 2-NT to Heathkit VF-1 VFO > > I'm looking for a VFO for my "new to me" 2-NT. I've read where several > older VFOs will work with some modifications, mainly converting to grid > block keying. Has anyone had experience with the old Heathkit VF-1? I > believe it has to be modified for grid block keying but I'm not exactly > sure how to accomplish that. I also understand that they are known to > drift a lot. Could that be somewhat remedied by replacing some of the > components with newer ones? > > TNX in advance for any advise! > > Gary N2UM > > _______________________________________________ > Drakelist mailing list > Drakelist@zerobeat.net > http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
