I agree on the explosion Brett!
If the choke and coupling cap are both large enough there should be
no change in the output waveform than if it were connected to a resistive
load. Perhaps it is the capacitance of the choke windings that is throwing
it off. It would be interesting to know what the free resonance of the
choke is. Or perhaps too much RF bypass capacitance in the RF deck. At any
rate I can't help but think that a smaller coupling cap would create
resonance which would put a reactive load on the modulator as would too
little reactor. This would make the modulator to see a different load Z
depending on modulating frequencies. In turn there would be intermodulation
distortion. And a shift in phase relationships of frequencies that make a
certain wave shape.
Interesting subject!
John, WA5BXO
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of Brett Gazdzinski
Sent: Tuesday, November 25, 2003 11:03 AM
To: [email protected]
Subject: RE: [AMRadio] Re: Modulation transformer ID and repair
I was talking about the pass capacitor, using a big one seemed
to interact with the choke and mod iron, a big cap had the sound
muffled, or something, I was disappointed with the results.
I tried changing the size of the cap, and found 4 uf I think
sounded natural.
I had tried all the way up to 40 UF.
The power supply has 70 uf or more in it...
Now that I actually have a good mike and preamp, maybe I should try
other values again.
More farads in the power supply is always better, but you need step
start or some way to bring it up gently.
Some run the voltage on all the time and switch the cathode, I never
tried that, easy with triodes likely, not sure about tetrodes....
WA3JVJ has a push pull parallel 805 mod deck with a huge string of
computer type caps, gives a full farad or more, and he runs the voltage
on all the time.
I think its quite crazy, about 60 computer grade caps in series parallel,
at 2000 volts or whatever, if one cap fails, the explosion and mess
will likely be very nasty!
Brett
N2DTS
t/mailman/listinfo/amradio
