[AMRadio] Class AB and B audio XFMRS

w5omr at satx.rr.com w5omr at satx.rr.com
Tue Mar 14 22:22:59 EST 2006

> Just because  its mil-spec freq response is +/- 1db is  100-3000~ 
> doesn't necessarily mean it is limited to that response.  It simply 
> that it is guaranteed to be +/- 1db over that range.  Depending on 
> manufacturer, it may actually have a much wider range.  I have seen 
military items 
> rated at 300-3000~  that were actually more like 50-8000~.  A good 
> is the T-368.  The stock audio is very restricted, but if the low 
> audio is redone, the xmtr has good enough iron to sound near 
broadcast quality.

That's the exact point I was attempting to make... just because it's 
garunteed to be +/1 1db at whatever range of frequencies, doesn't mean 
it won't do better.  How much better is a matter of measurment.

It does however, Don, make me feel much better about using a T-368 
modulation transformer in the 250TH modulator, with the reactor across 
the secondary. :-)

That mod iron, as I've been told on the air, does allow for some fairly 
deep low frequency responses.

My audio setup starts with a balanced-line output Sure SM-7 
microphonium, into a balanced-line in/out 31-band graphic EQ, into a 
balanced-line input on the modified Bogen PA system, used as the speech-
amp.  After that, the audio is taken directly off of the plates of the 
8417's into a 1:1 isolation transformer, of which hte secondary is used 
as a high-Z choke, while the audio goes to drive the bases of a pair of 
ECG164 Vertical output transistors, lashed up in an emitter follower 
configuration (thanks John/WA5BXO 
ref:http://www.qsl.net/wa5bxo/driver1.html).  The emitter output lines 
directly drive the grids of the 250TH's.

73 = Best Regards,
-Geoff/W5OMR(m5 Houston, TX)

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