In order to get at the coils in order to disconnect their chassis leads (each grid coil is grounded to the chassis), I had to unsolder all of the wires of this assembly and carefully remove it. It was a challenge. I imagine that it's kind of like what people complain about with the Philco 'unitized' chassis (or whatever they're called).
I found that feeding AVC to the RF amplifier coil secondaries doesn't work to my liking, so that was kind of in vain. In some radios this may be necessary, or may work well. With everything being well shielded, all that's really necessary in this radio is to vary the gain of the antenna circuit. I wanted to vary all of the RF stages, since this is what the original volume control did. I have secured best results with simply applying AVC to the antenna circuit, though, so I can re-ground all of the RF coils (YAY!). AVC is applied to the antenna circuit by lifting the resistor in the antenna circuit from the chassis and then connecting it to the AVC line. With all of the RF coil secondaries being grounded, or if you were to feed them AVC, the RF bias volume control is omitted, but the 600 ohm resistor in the RF cathode circuit remains (different radios are different, but all you ever want to do is remove the volume control...not any other fixed resistors....and with a radio that varies filament voltage for volume, you'd put the filaments at full brightness all of the time...if you wished to modify such a radio).
This radio originally had a dual volume control--one section for the RF bias, and one section for phonograph control. That was gone when I received the radio, and all that took its place was a 100K control for the radio. I've always wanted either a dual control again, or just a regular audio control for both the radio and the phonograph (which isn't possible with the original design). Having AVC allows for the latter. A 1 meg control works well for me (center goes to grid, high goes to 1st audio secondary, and low goes to chassis). I wanted to secure AVC from the detector, because I found that the detector grid would swing quite negative with strong stations. However, its rate of negative swing didn't match the gain reduction needed at the front end with strong signals. I was able to obtain AVC via the conventional route--a diode on the audio. In superheterodynes, the diode is also the detector (unless there's a separate AVC diode, with a condenser off of the IF plate). This radio lacks a conventional detector diode, so a separate AVC diode is needed. I wanted to take AVC at the volume control (high terminal) in this radio, and not from the RF stages. The volume control I added is after the 1st audio transformer. A small silicon diode with low leakage did the trick. It feeds a high value resistor. I like using a 330K resistor, though a conventional 3.3 MEG resistor will work fine. I had success with the 330K when I was originally trying to vary bias in the RF stages, and I stuck with it when moving to varying the bias of the antenna circuit.
AVC action is quite nice, and I have a conventional volume control that serves both the radio and the phonograph. With AVC I am able to always drive the detector with a strong signal, so that it is operating above where it sounds distorted. This is really nice. I can turn the volume of the set down really low and still have clean audio. I couldn't do this when I was varying RF amplification for volume control. The audio would sound fuzzy and grainy when down low, since the detector was barely being driven negative, and didn't rectify well at those low signal levels.
If a station is really strong, I can also off-tune the antenna control, or use the 'long antenna' terminal on back (same as having a local-distant switch, but without the convenience). So far, though, the AVC circuit seems to take care of strong stations.
Here's something nice I thought up that would be a fine addition to any radio, though it's quite elementary....I'm surprised that I haven't seen it before. I rather liked the lack of AVC on my Majestic for listening to local music, because the music sounded amazing. It was so much more pleasing and life like than with any other radio I own. However, there are times when AVC is nice, such as when going from station to station, or when listening to a station that fades. What I'd like to do, and you can do this, too, is put an AVC rate control switch below the set. All that is required is an inconspicuous shielded wire that is run to the bottom of the set. You can mount a control in the rear of your set if you wish (any set you like, as long as it has an AVC circuit). The shielded wire would go to a rotary switch with 3 or 4 positions on it. The center wire, which would be connected to the AVC circuit, would go to the switch wiper. On the 3 or 4 terminals, various condenser values would be attached. The other ends of each condenser would be tied together, and would be connected to the shield. The shield would be connected to B- in the radio. I find that about 2 MFD is great for local listening. It makes the AVC really slow so that music sounds natural (note that grounding the AVC line so that it doesn't fluctuate would cause distortion with strong signals....AVC is still necessary....a large value condenser just slows down its rate of change). Then there'd be a .1 MFD condenser, which still allows music to be somewhat natural, but compensates for some drifting, and allows for going from station to station without blasing. If a large value condenser is used (say 2 MFD), you can still go from station to station, but strong stations will come in loud and distorted at first, and you will have to wait for the condenser to charge before they come down to normal value. This will also be true if you decide to switch on the large value condenser for music listening, but will only happen once. .05 MFD would be for interference and heavy drifing/fading. A slightly smaller value (say .01 or .02 MFD), if possible (some sets will oscillate with smaller values), would allow for even better compensation of drifting and fading.
To use the switch, you'd use one of the smaller value condensers for tuning around. Then, if you came across a stable station with music, or a station with extremely slow fading, you could switch to the high value condenser so that the audio sounded more natural, and not all condensed. For stations with heavy drifting or static, switch to the condenser that allows for the most natural listening, while still compensating for troubles encountered. ....A very simple control that can make a world of difference in your listening pleasure. Note that when switching to any of the condensers, if they aren't as negative as the AVC circuit, the signal will momentarily get louder until the condenser chosen gets charged up. With the 2 MFD condenser, this could be a couple of seconds.
Thomas
Thomas