[ARC5] RCA AVT/AVR: Strange Vibrations.

[David Stinson]

Whomever said vibrator power supply design was voodoo
had it exactly right.....

I got a chance to put a scope on the power supply.

The squarewave waveforms on the primary - 
Nominal 12 V PTP, are indeed "spiky,"
with a very nasty and fast rise-time, very short duration 
spike at the pin-7 contact up to 50 volts P-T-P during that 
contact's "OFF" time, which means it's originating in the 
other side of the primary (pin 1), I suppose.
Also a couple of lesser "nasties:"    One at half the peak
value of the primary square wave during the rise-time of
the pulse and one near the end of the square-wave peak,
10 volts above the nominal value.

However- the waveform in the secondary looks good.
The snubber is doing just what it should.
The secondary trace is 700 V PTP, just as one 
would expect for transmit B+ of 350 Volts with very little "noise."
Removing the snubber for a quick "snapshot" shows the 
nasty primary spikes in the secondary 
and replacing the snubber clears it up.

If I put a 22 uFd 400 VDC capacitors  
from the vibrator primary connections to ground,
that cleans-up the fast primary spikes, but dumping them 
that way causes so much current to flow through the caps 
that even these high-Voltage rated ones get warm
and the transformer overheats.  

So much energy getting eaten in that snubber,
yet it seems to be working.
Input current to the supply under full load transmit
is about 5 Amps- well below the specified 7.4 Amps.

So.... I installed a 10-watt wirewound resistor
(which also gets hot but can handle it).
I put the rig on the air for 30 minutes and have 
been making local contacts on 3880 KC with
the mighty 8 watts out.  The transformer runs cool
and everything but that resistor seems.... normal.

Here is the rig before I build a mount for it:

http://home.netcom.com/~arc5/AVRAVT/RCAonair.JPG

I dunno.... think I should count my blessings and move on??

TNX OM ES 73 DE Dave AB5S