DX100 VFO Troubles: Drifting up during transmission: Line voltage drop during plate voltage turn on with 600 watts pulled from the outlet may the problem. Check by first using the spot switch listening to the beat freq on the receiver. Then, turn on the plate voltage with transmitter fully loaded, and monitor the drift. If the filaments in the oscillator drops in voltage and slightly cools off the tube, the oscillator will drift! See if the oscillator returns to the original frequency when the plate switch is turned off. Cure: Use a variac to keep the voltage at >115 VAC during transmit. Or create a DC regulated supply for the filament string. Anything much lower than 115VAC and the emissions on the 12BY7 / 5763 and 6146s drops also. You may see this as gradual drop-off of grid drive during transmit... especially on TEN meters. I also rewired my VFO with heavy #14 copper. This was mechanically superior to the flimsy wiring that can cause drift and microphonics. Here is the big stability problem: Jumping during VFO freq adjustment on TEM meters. The VFO main variable has a rear ball bearing to support the cap shaft. It oxidizes and becomes erratic. I tried to clean it, but it was never perfect and always degraded again. I finally REMOVED THE DAM BEARING THING and the problem was solved. The bearing is not needed as I initially thought. The shaft is very stable without it. I hope some of this helps. George AB2KC
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of russ dworakowski Sent: Tuesday, January 07, 2003 1:53 PM To: [email protected] Subject: Re: [AMRadio] DX-100 vfo To the group: I am having difficulty witha different VFO- a VF-1 or same as used in a DX-100. I know you guys are talking CE20- just a question- my VFO is tracking reverse in frequency- like when you go down in frequency on the display, it is actually going up in frequency. Is it possible that the end point adjustments are so far off that they could cause this? Russ >From: Gary Schafer <[EMAIL PROTECTED]> >Reply-To: [email protected] >To: [email protected] >Subject: Re: [AMRadio] "Reply" button got me... >Date: Sun, 05 Jan 2003 14:46:35 -0500 > >Hi Larry and others, > >I too have a 20A. Have had several over the years. I found that to get good >output on 40 meters that the 1625 has to be in very good shape. Being just >a >little weak makes a big difference. > >Also you need to adjust the padding coil (miniductor stock) that is across >the >1625 tank coil in the vfo. You adjust it by spreading the turns on one end. >If I >remember right, the padding capacitor under the chassis needs to be peaked >on 80 >or 20 meters. The other bands are adjusted by adjusting the miniductor >coils for >maximum output. (It doubles or triples for other bands) It takes some >messing >with to get them right as the Q is pretty high. When you replace the top >cover on >the vfo things change so you have to compensate for that when adjusting. >I watched the output of the transmitter (at less than full power) on a >meter >while adjusting the coils. Then watching how much it changes with the >cover, you >can get a feel for how much you need to adjust it in the opposite direction >so it >will be right with the cover on. Adjusting the coupling loop (knob on front >panel) will detune the tank a little too on 40 meters. > >On one vfo that I have I tried slug tuned coils in place of the miniductor >stock >to see if they could be substituted. I found that the slug tuned coils in >place >of the miniductors did not give near as much output on the vfo so that was >abandoned . > >I also tried to use a higher harmonic for 10 meters and shift the vfo with >an >additional padder capacitor (similar to what is done for 15 meters). I had >a >spectrum analyzer to watch all the harmonics at once but found that I could >not >get enough isolation. Some of the lower harmonics would end up in the >output. I >got it to work but tuning was very tricky and if not looking at the >spectrum >analyzer, the wrong harmonics would get right through the 20A. I gave up on >that >idea. > >I do have a vfo with the 10 meter kit in it. The crystal oscillator in it >is run >directly from the 20A's high voltage. When keying the transmitter that >voltage >drops some and the crystal oscillator starts to drift. I think that I tried >running it from the regulated 105 volts one time but that dropped the >output too >low. I have never gotten back to it to try and solve the drift problem. >Other >than that it works pretty well on 10. > >I also have a Phase master vfo that I have yet to hook up. It is built on >the 458 >parts but rather than use harmonics they have separate crystals and >heterodyne >for the other bands. It may double on one band, I can't remember. The >schematic >of it is in Stoners SSB handbook. > >73 >Gary K4FMX > > > >Larry Szendrei wrote: > > > Mike et. al., > > > > My CE20A has about 1/2 the output on 40M as it has on the other bands > > (160, 80, 20, & 15) in spite of the fact that the CE mods to cure this > > in the VFO-458 have been implemented. As I recall the VFO output is > > tripled for 40M, and only doubled or on the fundamental for the other > > bands. My VFO doesn't have 10M capability, so have no experience with > > 10M on this rig. > > > > 73, > > -Larry/NE1S > > > > MIke Wells wrote: > > > > > > I'm enjoying the 20A discussion. I have a 20A that I want to get on >the air > > > so keep the messages posted here for the benefit of others. > > > > > > Tell me more about the VFO, are you having good luck with it on all >bands? > > > I've only got mine working on the low bands, no oscillation on 40 >meters. > > > Suggestions? > > > > > > 73, > > > > > > Mike W0FD > > > > > > Subject: [AMRadio] "Reply" button got me... > > > > > > Regarding the previous posting to the list: it was unintended. The old > > > "reply" button got me again! > > > > > > If you're interested, read it. It's part of a discussion Jim Candela >and > > > I are having about a vintage SSB exciter, the venerable Central > > > Electronics 20A. If not, the "Delete" button is much more predictable >in > > > its effects than "Reply." :>) > > > > > > 73, and back to AM... > > > > > > -Larry/NE1S > > > > > > _______________________________________________ > > > AMRadio mailing list > > > [email protected] > > > http://mailman.qth.net/mailman/listinfo/amradio > > _______________________________________________ > > AMRadio mailing list > > [email protected] > > http://mailman.qth.net/mailman/listinfo/amradio > >_______________________________________________ >AMRadio mailing list >[email protected] >http://mailman.qth.net/mailman/listinfo/amradio _________________________________________________________________ MSN 8 helps eliminate e-mail viruses. Get 2 months FREE* http://join.msn.com/?page=features/virus _______________________________________________ AMRadio mailing list [email protected] http://mailman.qth.net/mailman/listinfo/amradio
