[AMRadio] Modulation transformer ID and repair

[John Coleman]

Putting the blocking/coupling capacitor in the ground leg of the modulation
XFMR keeps DC current from flowing through the secondary and leaves the HV
on the secondary so that the potential difference from primary to secondary
is the closer to the same voltage there by lessening the possibility for
arcing between the windings.  There is no difference otherwise in the
operation parameters of either circuit.  

While on the subject, in the circuit where there is no ground connection,
the audio return path is through the power supply filter capacitor.  This is
effectively reducing the amount of capacitance since the coupling capacitor
and the power supply filter capacitor are now in series with the audio path.
This is OK if the power supply filter has enough capacitance. It even has
one advantage, the need for a very HV capacitor as a coupler is reduced to
the DC voltage drop across the modulation reactor.  

In the circuit of Don and mine where the audio path is to ground, there is a
slight reduction in hum from the power supply as well.  

-----Original Message-----
From: amradio-admin at mailman.qth.net [mailto:amradio-admin at mailman.qth.net]
On Behalf Of Geoff/W5OMR
Sent: Sunday, November 23, 2003 4:52 PM
To: amradio at mailman.qth.net
Subject: Re: [AMRadio] Modulation transformer ID and repair





> Don's circuit didn't come out to good here so I redrew it and it can be
> viewed at this link 
> http://wa5bxo.shacknet.nu\HAMPICTURES\mod-reactor-circuit.gif
> 
> I pretty sure this is what you had in mind Don

When I had my reactor in the 250TH rig, in the larger rack, I came up
with around 49.9Hy @ 400mA by seriesing 3 chokes.  two 20Hy's
and a 9.9Hy @ 400mA.  I had a 5uF choke tied between the high-side
of the modulation transformer and the final side of the Class C B+ supply.

The other end of the modulation transformer was tied directly to ground.

What would be the difference?

73 = Best Regards,
-Geoff/W5OMR

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