Using ricebox for boat anchor VFO

[KX5JT]

I might want to temporarily use my TS-570 to drive the Viking II.   It can be dialed down to 5 watts.   Too much?  What is the easiest way to address this?

[kb3rdt]

This might help ya!

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

[KX5JT]

Ah I should have searched first....

http://amfone.net/Amforum/index.php?topic=8619.0

sorry

[Opcom]

I use a TS430-S as the VFO and driver, and am happy with it. It's easy to set to 20W wch is what I need, but 5W would be very touchy with the front panel control.
A 6dB pad might be appropriate to get there. I thought about a 10 turn pot but the 430 is not leveled or very well regulated as far as I understand it. Leveling would be a nice addition.

The TS570 is pretty new in comparison, probably would work great if you can set 5W without a micrometer on the knob!

Lesson learned with the TS430-S is the dissipation in the radio is a lot, maybe 40-60W at 20W out.
Solution was to add a fan at the back of the rack in which it's mounted to blow directly at the rear heat sink at all times and it really keeps the set cool.
Big improvement is a small MFJ automatic tuner between the box and the driven circuit.

[KX5JT]

Yes 5 watts is not a problem.  Power out is menu selected so I can set the rig for 5 watts at 50 ohms of course... my question is what do I need between that (5w @ 50 ohms) and the VFO input on the Viking II.  It feeds the grid of the buffer/oscillator.  I COULD bypass that stage like the link above shows and pull the tube and use a cap, but I'd prefer not to.  

5.5  to  8v into a 25K ohm load is what the Viking VFO manual says is used.  That's like 2 milliwatts

Would building a step attenuator do the job?  I don't know how the kenwood will behave since I'm sure it's not going to be a 50 ohm load.  Step attenuator and a directional coupler?

Maybe I'm just over thinking this.

[KD6VXI]

The idea of a pad is a good one.

Let's your radio see 50 ohms,  regardless.   Also keeps her generated in the xmitter / vfo down,  as it's running closer to designed power output.

2 to 3 db should be enough to keep everything happy.

--Shane
KD6VXI

[w1vtp]

I like Ken's (W2DTC) solution:  simple, follows the KISS principle and is a proven way to hook up a rice box to a V2.  The other approaches will work but requires some "figgerin"   Ken's approach?  Remove one tube and couple the input to the output of that stage with a cap and there you are.

Al

[KX5JT]

On Ken's schematic, I don't see how that's a 50 ohm load though.   That's the only thing that I'm concerned about there.  Won't the ricebox foldback power if it's not transmitting into a match?  

Or is that part of the design!?  Is the folding back how he obtains what he is calling "flea power"?

[Pete, WA2CWA]

If I were to try this, I would hang a 50 ohm load on the output of the 570 and then use Ken's circuit.
What's wrong with your 122?

[w1vtp]

If I were to try this, I would hang a 50 ohm load on the output of the 570 and then use Ken's circuit.
What's wrong with your 122?

Ditto on both points

[KX5JT]

I opened it up here at work with no way to check anything outside of a visual inspection.  My Viking II has very good workmanship but this 122 was obviously not built by the same person.  Key jack wire was loose and floating around and the soldering work is horrendous.   Almost every solder connection is a spiky lump of dull grey.  When I get an alternate "VFO" going, I'm thinking about tearing it apart and rework it then take it from there.  It was working a couple of weeks ago albeit the dial was totally out of calibration.  I would use the sdr receiver to find the signal and take it from there.  But it just stopped working out of the blue one time when I fired everything up.   No smoke or pop or anything, just a quiet refusal to oscillate.  

So this weekend I'll put power to it and make sure I have lit filaments etc, solder that keyjack wire back in place and maybe rework a few of the easier to reach joints and see what happens.  If that doesn't help, I really might just tear it down and rebuild.

[KX5JT]

So do I simply put a 47 ohm 5 watt resistor right across the coax jumper for a nearly matched load?

[kb3rdt]

I would do 10 watt one end to ground other to input with cap

[Pete, WA2CWA]

If I was going to do it, I would take a dummy load (10, 100, 1000 watt whatever), screw a coax T-connector into it; then short length of coax from output of 570 to one side of the T; connect the other side of the T with a short length of coax to the innards of the Viking II as per Ken's drawing.

Pl-259 to SO-239



Or maybe a BNC version depending on what's on your dummy load

[kb3rdt]

270 x 5 in parallel 5 watt 54 ohm be a 25 watt dummy load

[KX5JT]

How about something like in the link that follows?   It seems easy to build.  I was thinking I could put one end into my oil-filled paint can heatsink and use the tap to drive the Viking II.

http://www.nonstopsystems.com/radio/frank_radio_antenna_dir-coupler.htm