The AM Forum

I'm in the process of restoring a Viking II.  Worked my way thru RF and voltage issues and now have it running with both crystals and the VFO.  I have a bad chirp in either the crystal or VFO.  Any suggestions on where to start trying to resolve this? 73 Gary - W5GW

I shouldn't be the one who has the "expert" answer, but given that I have a viking 1 and 2, I'd be interested in this thread.

I remember way back when (1954) I used to have to detune my Xtal osc away from the peak on the other side where the osc output stops.  Wonder if  you are peaking the osc output and if you were to detune slightly the problem would go away

Al

The VFO should run at half frequency and double in the rig. If its a 122 VFO check the 6AU6, VR tube and all carbon resistors. Try a 6AH6. The connecting coax should be as specified. In very early 122's there were a few paper caps.

Carl

It won't help with the crystal but since I don't run full break-in I use an extra set of contacts on the T/R relay to keep the 122 keyed while in transmit.  This keeps it chirp free.  On 40 meters you can set the VFO for 160/80 operation rather than have the VFO on the same frequency as the rig and this will avoid problems with RF getting into the VFO and causing problems.  

Are you using real FT-243 crystals or some of the new ones that have a small crystal inside the FT-243 case?  I have a couple I bought from Bry for 3885 that I use in my Ranger and Viking 500 and these drift slightly for a couple of seconds after hitting the PTT.  This isn't a problem for AM but they would sound ugly on CW.

Attached below is a cheat-sheet I made for the Viking II settings.

If that oscillator stage has a VR tube running it's B+, see if the VR tube is glowing all the time or not.

I changed the oscillator tube (6AU6) in the Viking II and the chirp improved a bit, but is still there whether I use a crystal or the VFO. 

I am keying it from the Viking II.  I did note that the OSC current is only 10-12 ma (no crystal or VFO, drive zero, in standby) whereas the manual say it should be about 20 ma. The Clamp circuit seems fine and idle current on the 6146s is about 55 ma.  Other voltages seem fine.

I have tried setting slightly off the peak on OSC and Buffer and some different loading settings, but that didn't seem to affect the chirp.

I suspect the issue is in the 6AU6 oscillator circuit or the buffer in the Viking II since I see it with both the VFO and the crystal.

Thanks to all for your suggestions - still investigating...

Now you know why everyone knew who had Johnson transmitters back in the 50s. 

Is this chirp a frequency chirp or a power chirp?

I wonder how long the chirp is? Is it 300ms, 3 seconds, 10 seconds, or what? If the chirp is in seconds, then maybe the filament voltage is dropping key down. If so, some 6AU6's will be better than others.

If the chirp is real short, look at the +300V B+ when keying. Looking at the schematic, C11 in the power supply could be 50 uf or 100 uf (450v) instead of 15 uf.

I am attaching the schematic.

Jim
WD5JKO

My Viking I with 122 didnt chirp in the 50's and the same setup I use now doesnt either.
Most chirp is from the VFO as mentioned earlier. The Viking PS may need new filter caps or rectifier if it cant handle the load.

Use only real FT-243 crystals, not the commonly sold ones with a miniature crystal inside the case.

Yes, the chirp is about 1/2 a second, or less.  I have been on the thread of looking at the power and agree that is likely a good place to start.

Thanks,

Gary - W5GW

I looked at the schematic and see that there is no VR tube in the Viking II.  There is one in the 122 VFO.

I ran my Viking II on 3733 kHz tonight with the 122 VFO and with a 3733 crystal, no chirp at all.

If you still run a tube for the +300 V rectifier, it may be weak.

This chirp is elusive. 

I checked the power caps and they are fine.  Someone recently replaced them with Sprague blue electrolytics.  Ripple is minimal on all both low B+ and high B+. 

Replaced 6AU6 OSC tube (that helped considerably).

It's screen resistor was also a tad out of tolerance. 

Tried different crystals and in different places in the crystal bank. 

Detuning the OSC control helps some.

Little difference in chirp between the crystals and VFO so am concentrating on the Viking II and in the OSC stage.  I can hear it (the chirp) when I key the Viking with no plate (B+) applied.  May look into buffer stage next.

One thing that is still troublesome, in accordance with manual, with crystal selector set to a position with no crystal or VFO, the 6AU6 current should be about 20 ma.  I only get 12 ma.  Yet I can get more than enough grid drive.  My carrier (other than the chirp) sounds very nice.  Also the AM modulation listening back thru my receiver sounds very good. 

Maybe I ought to chalk it up as a characteristic of the beast.  :)

I suggest you look at the RF out on a scope while keying a series of dits or dots. A power chirp will be readily apparent. Possibly you have both a frequency chirp and a power chirp?

Since the chirp is present with either the VFO or a crystal, I'm thinking a power chirp is the dominant chirp. It would be pretty unlikely that a frequency only chirp would be the same on both the VFO or crystal with the same time constant and frequency shift. The VFO has a regulated screen voltage too, and it is electron coupled meaning the VFO oscillator is isolated somewhat from the output section.

I'm with Jim W5JO that these transmitters might have some form of chirp that might vary from unit to unit. Just because somebody elses Viking II doesn't chirp does not mean the Johnson design is solid to the point where all Viking II's are chirp free. Then factor in the effects of time (corrosion), resistor drift, capacitor leakage, tube aging, poor solder joints, kit build errors, and long ago OM modifications, repairs, etc. and we pretty much can conclude that each Viking II is unique.

If you see a power chirp on the scope with dits or dots, then look at the LV B+ on scope (suitable 10X to 100X probe). My bet is the LV B+ shows similar effect. Why? Well it has a pi C-L-C filter, and no bleeder resistor. The LV B+ will vary quite a bit key up to key down. The only way I know how to fix that is to red line the schematic and make changes.

As a test though, see what happens by bridging the LV B+ line with something like a 100uf 450v capacitor. This will change the time constant. Does it also change the CW chirp behavior?

Edit: The W8JI site talks about chirps on Rangers, and Valiants:

http://www.w8ji.com/johnson_vfo_chirp_jump.htm


Jim
WD5JKO

Have you tried a 6AH6 in the VFO yet? That is a 60 year old cure for 122 and early VF-1 chirp.

And also try not keying the VFO, there is no need to do so unless you are trying to run full break in.  There is a reason differential keyer circuits were developed to reduce the problem of chirps and clicks from a keyed VFO.

  He gets the same chirp on the crystal as he does the VFO. How do you explain that?

Jim
WD5JKO

A chirp but is it exactly the same chirp?  There could easily be a separate root cause for each source of chirp.

I agree with Roger plus he still hasnt even bothered to answer what crystals are used; there are a lot of those phony 243's out there.

I like to tie multiple symptoms to a single problem whenever possible, and only jump to the multiple problem theory when the first attempts don't pan out. Then again, the problem description has been somewhat vague. Maybe the chirp is in the receiver?  :D

Jim
WD5JKO 

Did you change C15 and C17?  I know they are micas, but one was leaky in my Viking II.  I found it before I ever used it on CW so I don't know if it would have chirped.

Why spin wheels when the most basic steps havent even received an answer?

Some thoughts...A lot of these old rigs use the Modified Pierce. The advantage of using the Modified Pierce ECO in the rig was that you could drive it with a VFO without instability using a simple switch on the crystal bank. A conventional Collpitts requires a another pole to properly disable the feedback so you can drive it externally without having to blast the drive. The Pierce is ready to go on VFO with a simple switch. The HW16 uses the same circuit except it grid block keys the oscillator. The problem is that the Modified Pierce is one of those circuits that is just too good to be true - it is simply a crappy oscillator having very low crystal current and and weak feedback on an unbypassed screen. And the HW-16 chirps as well. It is also fussy about crystals and the plate tuning too.

You could convert the thing to a conventionally keyed Collpitts ECO with a bypassed screen. The Handbooks are full of these circuits for a reason.

But...you can tame the Pierce.

All this said, drooping screen voltage is likely the biggest offender however; and regulation will help. Here are some things to try. You would insert a small choke between the 68K screen resistor and the screen. The screen is part of the feedback for the crystal and is acting like a plate so you do not bypass it. You should see very little difference at this point. All you are doing is raising the impedance a bit.

Now put a 105V regulator tube or three 33V Zeners from the RFC-resistor junction to ground so you get regulation key down. A 0.01 bypass cap here will be required. And you will likely need to reduce the 68K resistor to something like a 15K 1Watt.

The Feedback can be critically controlled by adding a cap to ground off the screen from 50 to 330 pF.

Mike WU2D

My memory has been jogged by Mike.  I did have a couple good crystals one time that would not oscillate in the Viking II.  After looking at many other Johnson transmitter schematics I added 10 pf to ground at the screen and then the crystals oscillated.
* 6/4/11 - I also changed C14 to 62 pf from the original 50 pf.

Also, has the chirp been confirmed on more than one receiver?  I had a transceiver one time that would pull in frequency based on receive signal strength; the Heathkit HW-101.  This was noticed while listening on 40 meters to CHU's time beep.  When the beep drove the s-meter farther up scale, the tone of the carrier shifted.  The engineers had applied AVC to the 1st mixer stage, in which the loading change of the mixer changing conduction pulled the heterodyne crystal oscillator stage!  I disconnected the mixer grid from the AVC bus.