The AM Forum

Good Afternoon All:

I am in the process of "re-kiting" a basket case Knight V-44 VFO that I picked up at a hamfest.  It was a disaster.  Rusted in places from a damp basement for who knows how long.         Challenge accepted.

Bought a manual off eBay and while I waited for it to arrive, I completely stripped the chassis on the VFO and the power supply and am planning on putting in all new resistors and capacitors.

Used a wire wheel in a drill to remove the rust.  Looks 1000% better.

Rewired the Power Supply unit.

My problem is the the two slug-tuned RF coils on the VFO Output.  Both of them have a dried out and mushy coil form.  The metal clip is rusted out (likely from being mounted on a dissimilar metal chassis; causing the coil form to degrade terribly.   I want to replace these outright.

The manual arrived today, and it, the parts list or the schematic do not tell me the uH value of the coils.

Question: Does anyone out here know what the inductance value ought to be, and even better, if there is a current JW Miller part number that I can get from Mouser, Antique Radio or whomever?

This is a Clapp Oscillator and has a buffer.

Another Question:   In CW mode, assuming you connect a key to the VFO, grounding the cathode with a 2.5 uH coil in line between the key and the cathode keys it. Is there anything that I can do to bolster the stability (and eliminate chirp) in the VFO circuit?


Another question/your thoughts: Guessing the 2 780 pF 1% silver micas which present an in-phase voltage to the grid and cathode if the Oscillator tube to make the oscillation....  Is this the main hinge-point for stability in a circuit like this?

Also, when I rebuilt the power supply and used a new electrolytic, I get 260 volts DC (about 1 volt of AC ripple I see) and the schematic calls for 250 volts.  Guessing this is measured on a VTVM as opposed to a DVM. Do you see this as atypical?

Lastly, the filament winding output is 7.1 VAC, which is a tad hot for a 6.3 VAC filament.  Is this normal to see if the load is not present on the output of the secondary/filament windings?

Any info you might have would be appreciated.  I will also cross post this to FB and and forward any replies from there to here.

73--Wally W9BEA

Wally,

   You have taken on a big project. The V44 is a pretty neat VFO with a built in power supply. But that built in power supply adds extra heat to a VFO, and that leads to drift until the thing is at temperature. By at temperature, I mean the thing gets HOT!

   I attach a PDF that you might find interesting. Since you mentioned CW, my madness in what I did might not fly for you. The heart of what I did was to incorporate the XLOCK-3 VFO stabilizer into a V44.

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

   The VFO output coils are just a broadly tuned output full of harmonics. The VFO oscillator is always on 160m, and the 2nd stage is a doubler. To get to 10m, you have to multiply 16X....Can you imagine that drift?

Jim
Wd5JKO

So,  a hundred hz of drift would be 1.6 kHz on ten?

Wow.

Love me some modern day stuff sometimes!

--Shane
KD6VXI