The AM Forum

Hi Everyone, I've been having an interesting problem and can't seem to locate the fault yet as to why my Viking Ranger is doing this.
Problem is: low but loud enough to hear high pitched buzzing, more of a screeching from the LP1 Transformer when the "Audio" is more than 1/4 the way turned up.
Note: It goes away on Transmit.
 
-No mic connected (but it will do so even if mic is connected)
-Dummy load or Antenna or nothing at all on the back no difference will so the same thing.
-Properly tuned on 75m Band
-Checked for bad tubes
-Checked for bad Caps (was re-capped)
-Checked for bad resistors
-Had the mod done with the "in-tube-socket" keying circuit.
Note: if I bring the Audio knob right to the threshold just before it screeches I can trigger the noise by hooking up the mic and keying and UN-keying the transmitter. This is pointing me to the relay or PCB that was installed however I may be overlooking something?

Question: Is it normal for the Johnson Viking Ranger to have a screeching in the transmitter when (not being keyed) if the [Audio] is more then 1/4 opened? If not (as I suspect) what then might be the cause of such a thing?

Thank you all for your time and comments.
Samson VA3ACJ
Have a great week everyone.

Hi,

You might try a mod that was found in my used Ranger II (I can take no credit).

The PTT relay used has a third set of contacts, 3PDT not DPDT.
The original owner has the extra pole switching the screen supply for the modulator tubes.  In receive position, the modulator screen supply is open, hence the modulator tubes are cut off.  In transmit, the screen supply is normal.

This mod also results in a much cooler transmitter, without wasted modulator
power during receive.

73,
Ed Knobloch

To amplify my previous posting, no, it's not normal to hear a screeching sound
in receive.  It could be due to an ultrasonic oscillation through the modulator.
The relay mod I proposed would definitely cure it, but it may be possible
to cure it by adding loss to the amplifier input stages, so that that
the required conditions for oscillation are not met.

You might try adding a 470 Ohm resistor (or so), either carbon composition,
a carbon-film or metal-film type, in series at the control grid of each tube
in the modulator (with the exception of the first stage of the preamp).

That may provide enough loss or change in phase shift to cure the self-oscillation
you are witnessing.

hi K4PF Ed and welcome to the forum .... as to the screech in the audio a possibility is loss of bypassing in the audio chain due to electro cap loss of capacity ...a scope should give you a better idea of what's going on

Thanks for the welcome, "Beans".  Seems like a friendly group.

Even the 0.1 paper decoupling capacitors in the plate supply
of the Ranger's pre-amp stages deserve a checkout.  A decoupling capacitor
breaking down may result in the unloaded modulation transformer
making crackling sounds.  Have you got access to a scope?

I've been working on my set up for testing the stages with a proper scope and oscillator it's taking me some time but almost there. I was able to adjust a few things in the Transmitter and to learn some of the modifications that have been done to it. I believe it's because of the mod that has been done as to why the problem is occurring. The Screen's are not being turned off with a key-circuit and so I'm making a decision to put things back to original tube rectifier and no TX/relay. I can get around this by simply turning the selector to stand-by when no in use so not sure if it's worth all the extra time and effort to mess with it or just use it as is. Either way I'd like to learn more about this transmitter and how it's designed.

Thank you all for your help and advice.
VA3ACJ     

This may be of interest,

https://www.frostburg.edu/personal/latta/ee/ranger/ranger.html


He does a good job splainin the transmitter.



KLC

Hi,

I think you are right to revert to the original factory condition,
since you are unsure of the 'mods' done, and whether they ever worked.
Johnson never offered a PTT relay as stock in a Ranger or Ranger II,
so they felt confidence in the panel-mounted mode switch.

Do you have a copy of the Ranger kit assembly manual?
It has many photos which would be helpful in reverting to stock condition.

One thing to be cautious about is to make sure the mod. transformer
has a good load across its output when testing - either a correctly loaded
Ranger rf section into a dummy load or a string of 115V lamps in series
across the modulation transformer secondary.
(Say. four 15W 115VAC incandescent lamps in series across the mod. XFMR
 secondary, to absorb power at roughly 600 Volts peak).

If the modulator is tested without a good load, the output voltage could soar,
perhaps causing insulation breakdown within the transformer..

Johnson included a spark gap across the secondary of the mod. xfmr
in the Viking Desk KW, to protect the transformer.

73,
Ed Knobloch