The AM Forum

Getting further along in my Viking II restoration, with the replacement for the open R13 on its way through UPS.  Was originally thinking of staying strictly "rockbound"  ;) with it on 3875 & 3885, but last few days have noticed some of the East Coast crowd moving around a bit, so a VFO of some type is under consideration.  Not particularly interested in using a vintage tube VFO  :P - want something that is up to modern stability standards.  Was wondering if anyone is marketing a solid-state VFO (either kit or fully assembled) that could be considered "boat-anchor compatible?  :D  Digitial readout would be a plus, but not an absolute necessity; if it has enough output to drive a tube rig, it'd probably be capable of driving a freq. counter I already own as well.  I'd also consider doing a scratchbuilt VFO if anyone has any particular design recommendations (such as an ARRL Handbook design that's known to work well).   :)  Tom WA1LBK 

See: http://www.wa1ffl.com/

Also: http://amfone.net/Amforum/index.php?topic=34438.0

Also: http://qrp.kd4ab.org/1999/990626/0029.html

Thanks for the info, Pete!  ;)  Sounds like either one might fill my requirements.  :)  Even though it's the more expensive of the two, the WA1FFL DDS unit looks VERY interesting. 8)  Kind of hilarious using state-of-the-art DDS tech to VFO a 1950's VikingII for AM use  ;D, but I'm using to doing things of that nature.  One of my other hobbies is garden railroading (large-scale model trains running on an outdoor layout); most of the trains are models of 1920's-era steam locomotives, but they're controlled via a system known as Digital Command Control (DCC), which sends high-amplitude digital packets down to the rails to provide both power & control information to addressable decoders installed in the locomotives; greatly simplified wiring of the railroad.  I also have a couple of live-steam locomotives  8) - (they burn butane for fuel) - controlled by modern 2.4 GHz. digital spread spectrum RC systems!  ;D  (enter my callsign into the YouTube search engine if you want to see the trains!).  Thanks!  ;)  Tom WA1LBK

Very very cool train stuff. I loved watching it.

Maybe you should try to find the 122 matching VFO, I understand it is very stable.

Bill

http://www.cumbriadesigns.co.uk/x-lock.htm

Here is a VFO stabilizer kit based on Huff and Puff circuitry that can be applied to an existing VFO.

Tom,

I am using the Pongrance vfo with the wa1ffl buffer amplifier on my Viking 1.  The Pongrance vfo works fine but the output is very low.  I had to change the feedback resistor on the buffer op amp to get enough drive.  Perhaps with the wa1ffl vfo, which the buffer was made for, it would work fine as designed.  Good luck.
Chris

Bill,

    Having done two of these X-Locks using vintage tube type VFO's, I agree.

A couple of big concerns here are:

1.) The load on the VFO, and tube B+, and screen voltages need to be constant. Same with filament voltage.

2.) In most cases a VFO for a Viking II is keyed. This rules out all the discreet Huff & Puffs since they only lock AFTER keying.

With the latest version of X-Lock (3.0), this thing can accommodate a keyed VFO so long as the keying shifts the frequency. The VFO must run all the time. The link by Pete in the second post in this thread describes what I did using X-Lock with a keyed VFO.

But this might go back to item 1 above, and if a Johnson 122 VFO does not provide a constant load, then X-Lock will lose lock and then require at a shifted frequency.  Adding a buffer stage, voltage regulators, etc. to the VFO can get involved. But then again, so can a DDS project with making the box, power source, shielding, VFO amplifier, keying circuit interface, etc....all doable, but IMHO beyond a one weekend project...

Jim
WD5JKO

How about this?

http://w2dtc.com/w2dtc-hi-fi-viking-ii/2007-0711-vikii-vfo.jpg

  KB3RDT Carl

Hmmm- have to admit that's an intriguing thought 8) , Carl!  - Particularly since I have at least 2 modern solid-state HF rigs  ;D currently sitting around unused.   ::)  Have my ICOM IC-706 MKIIG which I used to run mobile before I changed vehicles a year-&-1/2 ago; & my commute is nutty enough  :P that I'm not even thinking of installing an HF mobile rig in my new vehicle (2012 Honda Odyssey).  Decsisions, decisions... ;)   Tom WA1LBK

Just be sure to give ricebox a 50 ohm load .... I suppose most riceboxes will still only crank down to 8 Watts or so minimum rf out .... a little figuring shows 8 Watts into 50 ohms gives 20 Vrms ... this is equal to 56V pp which may overdrive the 6aq5 buffer .... it depends on the ricebox .... just may have to pad it down a bit ....not a big deal

Yep, already planning a 50 ohm load for the '706MKIIG if I use it for this purpose.   :) I'll check first what the minimum power level is that I can set 706 to first with a wattmeter (it has 10 power level steps, 10 = full power, 1 = min. power); if like most of the 100-watt class "riceboxes" it puts out 40 ~ 45 watts on AM, that might translate to 4 ~ 4.5 watts at power level "1".  Even if it doesn't, shouldn't be any more than 10 W. out.  I'll build the load into a minibox with a variable cap to adjust the amount of RF I couple to the Viking II; at this point, though, still battling modulator problems with the V II (see my "Viking II R13 / R30 Questions" thread for a "blow-by-blow"  ::) on how that battle's going).   ;)  73, Tom WA1LBK

Make it easy.

Shove a (usually)  negative voltage onto the ALC of of the Icom.  This will allow completely variable carrier power.   It will also give you decent AM out of the Icom....  This negates the ALC action internal to the radio allowing full AM.  I do this on my FT857 and have solicited good audio comments from Tim and Don.

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KD6VXI

I believe the plan is to use it as a VFO so modulation isn't an issue. However, some Icom's I've heard, have a tendency on key up, to emit a momentary RF spike at full power, regardless as to where the RF carrier is set, so that should be checked.

I understand he wasn't going to use it as a transmitter,  was reiterating that the ALC injection is a he he fix,  as well as it would enable him to use it if needed.

The ALC the injection fixes that key down spike,  as well.  :-)

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KD6VXI