The AM Forum

Hello All,
            I blew the VFO "Chernobyl" resistor in my Valiant II the other night. Does anyone have any shortcuts or replacement tips for changing it out?

Any advice would be greatly appreciated. It doesn't appear to be an easy job, and I've heard of guys who have mounted them externally to keep them a bit kewler. What would be best?

Best Regards,
                   Joe Cro N3IBX

Yup......It had to happen Joe...
Take off the side of the vfo that faces the vr toobs. U can then get at the resistor. I was able to squeeze wires through the bottom of the vfo compartment up to where the resistor was connected and mounted the new resistor under the chassis. I used a 20K 10 watt WW. Radio works just fine.
Its not as easy as it sounds Joe.......but it can be done......just take your time and dont get pissed!!!!!!
Bill

Hello Joe: I just replaced my resister on the rangerll abt 3 weeks ago. I did the same thing as bill did on his reply, but it had three of us cussing and wondering why in the world would they put that resister in that difficult place. good luck Matthew KR4WI

There's been a recent debate which goes against the "relocate the 18K" school of thought. The VFO was designed by Johnson to heat up to a certain temp and then stabilize there.  Some say relocating the 18K resistor messes with that scheme, promoting additional drift.  I got a hefty Ohmite 10W WW that could survive a nuclear blast and left it in the VFO compartment.

Hey Joe.....Make sure you measure the voltage on the VR tube after you install the resistor.. 20K may be too high.. It was too high for my Ranger and Valiant. With the Tim Tron modulators installed I was pulling the voltage on mod peaks so I went to 17-18K at 10w and installed in under-the-neath.

73

Joe,

I have heard the same argument regarding the temperature thing. I think maybe BYM could address that. I did mine, out of fear, and it's a Ranger II and it's rock stable and I mean rock! Cold to warm up in 30 minutes, a couple of hundred cycles. Thereafter, for three days, never more than 15 hz either way!

Pics are worth a thousand words so before:

(http://w8er.com/pics/before.jpg)

And after:

(http://w8er.com/pics/after.jpg)

That's a 20K 7.5 watt and what I had on hand.

--Larry W8ER

Good job, good pix Larry. When I did mine, my rationale at the time was that the stock 3W resistor was too wimpy, and upping it to 10W solved the problem entirely. The runaway heat was a symptom of failure, not a cause, i.e. in normal operation the VR and osc. tubes would never generate enough heat to break down a hefty wirewound, therefore relocating it out of the VFO box was not necessary, even though the Timtron gospel says the opposite. Anyway, being lazy, not moving the thing worked out fine for me  :D

Larry......You are correct with the 30 minute stability in your Ranger II.  The Ranger II and Ranger I have different VFOs.  Not much but the II has a temp. compensating butterfly.  Yours is obviously adjusted right on. You can go to far in either direction and the drift will be either positive of negative.  I can attest to the complete melt down of the VFO board. If anyone is interested they can check out ER Feb. 2001.  That was a Ranger II with a very fried board around the VR tube.  Now that was a fun replacement job and will make a believer out of anyone. Ron W8KYD now owns that Ranger II.

73

Everybody,
               I GREATLY appreciate your advice and many thanks again. Hope to have the old V2 up and running again soon.

Larry - BTW, your pics are SUPERB!!!

Joe........The pics are great cause I taught Larry all there is to know about photog....He's finally catching on....It's been a long haul..

73

Joe, I did the same thing as many.  I refurbished a very early version Ranger I a few months ago.  I replaced the "Chernobyl" resistor out of fear.  I used an 18K, 10 watt wirewound, relocating it to the underside of the chassis.  It was pretty easy as my Ranger does not have the bias rectifier circuit, thus no tubes in the way of the left side panel of the VFO compartment.  Typically, the resistor will lose value, although the one I removed actually doubled to around 35K.  I haven't noticed tremendous drift, although the longer it's on the more stable it is.

Joe,
yep, I did the 18K 10 watt resistor change to both the Valiant and Ranger 1 this winter after 10 years of worrying about a meltdown.  It really wasn't hard at all!
Like Bill said, you can take the side of the VFO off and there it is.  I didn't even try to get to the terminal strip.  Just cut the resistor leads near the resistor and bend them into a loop with your needlenose.  That will allow you to wrap your of wires around something for soldering.
In both rigs the resistor is now under the chassis.  The grommet leading through the bottom of the VFO box has plenty of room for your 2 leads going to the bottom of the chassis.  There was even a place to secure the terminal strip.

Git er done Joe!
73
TM W2ILA