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Old 30th Nov 2020, 4:19 am   #7
dtvmcdonald
Pentode
 
Join Date: Mar 2016
Location: Champaign, Illinois, USA.
Posts: 227
Default Re: Racal RA17C12 AGC

With the proper tube it meets specs, including rise and fall times, except for long time constant, which are double the spec because I have double the capacitance.
But there is no spec for overshoot.

I broke down and designed a circuit to simulate the AGC acccurately, not using
RF and a demodulator. I had done that previously, but I don't have the patience to
run it at realistic time constants and using nonlinear amplifiers. Amplifing 100 kHz for 10 seconds is not fast with nonlinear functions. I have in the past done such simulations
using real remote pentode tube models .... even simplified, 30 minutes to run. This did tell me the source impendance of the demodulator.

My current simulation is entirely DC and audio at 500 Hz. I'm using amplifier
gain models that are exponential in tube bias, different ones for 6BA6s and the 6ES8 and the 6DJ8. For the latter I use a sharp cutoff. I'm using real (and very good, including the current from the tubes in the absence of external bias) models of 6AL5s. After tweeking a bit the parameters this models the radio nicely with both the 6ES8 and 6DJ8.

Behavior is embaressingly bad with the wrong tube in the RF amp, in reality and in simulation.

So I played with the simulation to get it to work better for SSB. This re
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