Quote:
Originally Posted by Alejandro Lieber[_3_]
patrick-turner wrote:
On 16 Nov, 22:06, Alejandro Lieber wrote:
In figu
http://1fcr.com.ar/classB.jpg
you can see a very interesting diagram of the audio modulator of an old AM
Gonset transmiter.
A 12AT7 as voltage amplifier. one 12AU7 with both triodes in parallel as
power amplifier and two 6DQ6A grounded cathode, grounded control grid with
audio input to the screen grids working push pull as pure class B.
R211 and R212 are only used for measurement purpose.
Why would they choose to use the screen instead of the control grid as input
? . Any suggestion ?
--
Alejandro Lieber LU1FCR
.........
There are some who may connect g2 to g1, and drive both, a bit wild,
because its like tetrode mode positive FB, but its doable. For hi-fi,
one could also drive g2, but apply NFB to g1, also crazy because not
much NFB can be applied because Vg2 has then to be quite high, and its
high already as it is. Most modulators I've seen are mostly 807s with
UL OPTs and all done like a normal Williamson or similar, but OPT is
say 1:1 and sec does the business at RF amp
Zero bias 807 (1625) class B audio amplifier:
http://1fcr.com.ar/807classB.jpg
....
Patrick Turner.
--
Alejandro Lieber LU1FCR
Rosario Argentina
Real-Time F2-Layer Critical Frequency Map:
http://1fcr.com.ar
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Hi Alejandro- Looks to me the PS voltages are incorrectlty labeled on the 807 modulator at that link, the 300 & 800 should be reversed.
But here are more examples of Class B vacuum tube modulators. These were referred to as Zero Bias Amplifiers.
Cheers, John