[AMRadio] Ranger Audio... the Pics

Larry Taft ltaft at charter.net
Sun Nov 19 00:54:25 EST 2006

To repeat an earlier comment, try a load resistor on the output leads, 
say 5K or something in that range at least 20 watts and 50 watts would 
be ideal for full power tests.  Pull the 6146 and the osc tubes to get 
rid of the RF.  You have to have a load on the mod iron to keep things 
under control.

The waveform that is puzzling is the 6L6 in standby.  What is the 
amplitude?  Looks like we have a parasitic oscillation in the amp 
circuit and it could still be there mixed in with the audio on xmit.

There is hum too as it is showing up as a variation in the peak 
amplitude of the 500 Hz wave.

You'll have to put back the bypass caps to gain some control over the RF 
getting into the audio.  Maybe a few RF chokes in the audio lines to 
eliminate the RF.  As you have seen. sticking the scope probe into a 
medium or low impedance is OK usually.  But a high impedance like the 
6L6 grid introduces more errors.  Another antenna.


Jack Schmidling wrote:
> I did some more sig tracing and came up with some pics of where the 
> trouble seems to be.
> Putting a 500 hz sine wave into the mic input, I see a nice sine wave 
> until I get to the modulator tubes.
> The grid in standby looks close enough but when I go to phone mode it 
> gets flaky.
> The plates look really flaky in standby but look more normal in phone 
> mode but there seems to be a bunch of waves competing for the space.
> I posted some pics to http://schmidling.com/mod.jpg
> Comments eagerly awaited....
> js

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