First, I should include some construction & adjustment details for the controller board freq drift compensator mod.  Referring to the attached drawing for the compensator, I mounted all the components on two small pieces of perf board [with 0.10 inch hole spacing] except for the thermistor, TR31.  I installed the board containing C31,32,35, P31,32 & Q31, on a slightly larger perf board outside the shield can & the other piece containing C33,34, D31 & R31 inside the oscillator [center] section of the shield can.  I mounted the boards via two 6-32 screws through two vent holes in the shield can.  It may be necessary to file the holes slightly bigger to accommodate the screws.  I used both screws [with spacers & nuts] to mount the larger board, one about 0.75 inch long & the other about 1.5 inch or so.  I mounted the internal board via the longer screw & a hole in its center.  One other important construction detail I should mention is the thermistor, TR31.  It needs to sense the [slight] heat given off by the 15V regulator, U305 in order for this circuit to work.  I replaced the mounting screw for U305 with a longer one & mounted TR31 via this screw & an insulated spring clip.  I made the clip from a piece cut from metal flashing & glued some plastic cut from an old credit card to keep the ungrounded side of TR31 from shorting to ground.  This clip doesn't need to exert much force on TR31, just enough to hold it firmly against the inside wall of the shield can directly next to U305 on the other side of the can wall.  Use heat sink compound on both devices; the grounded side of TR31 goes next to the shield can wall & bend enough offset or standoff in the clip to accommodate TR31.
 
To calibrate, P31 only needs to be set so that the signal from TR31 never causes Q31 to saturate.  When the radio is first turned on the base-emitter voltage should be less than -0.5V & become more negative as it warms up & TR31's resistance drops.  Turn P31 CCW to make this reading less negative & vice-versa.  Next, as the radio warms up watch which way the frequency drifts; if the displayed freq drifts lower turn P32 CCW slightly to compensate & vice-versa.  My radio originally drifted over 12KHz but I got it down to about 3 or 4KHz.  Expect to tweak this about a dozen times or more to get it optimized.
 
Other Receiver Board mods [continued from first post].
[7] Replace detector diodes, D415,416 with 1N5817 Schottky diodes.  The original germanium diodes had a forward voltage drop of about 0.27 & 1N5817s read about 0.14V on a Fluke 77 multimeter & have a much higher reverse resistance.
[8] The original 1N4002 1A PS diodes ran a little hot as evidenced by discoloration on the PC board next to them.  I replaced them with 1N5404 diodes which are rated at 3A.  I had to ream the lead holes on the board with a 0.040 in. drill bit.  Also form the leads so there's about 0.75 in. between the diodes & the holes for better ventilation.
[9] Drill holes in PC board on either side of main filter cap, C511, for small cable tie to help secure it.  Be careful to avoid damaging foil traces on the board.
[10] Replace 390K resistor, R444, with small piece of perf board containing 100K resistor in series with a 100K, 1-turn pot to control AGC threshold.  This & the next mod are shown on a separate drawing which will probably be attached soon.  Adjust this pot for maximum volume without overloading & distortion on strong stations.
[11] Replace C475 & R464 with small piece of perf board containing a 1Meg resistor & 22pF cap in parallel with each other & in series with a 500K, 1-turn pot.  This pot adjusts the sound level in AM wide mode only; adjust for equal volume between AM wide & narrow modes.  Incidentally, I found that the source of the audio distortion is U404d when in AM wide mode; I'll probably dig deeper into this after it gets too cold to play outside.  Will advise if I find any more worthwhile mods.  I hope some of you find these mods as much fun & useful as I have.  73s.

Since last fall I've made a few more improvements to this receiver in three areas; what follows is a description of these wiring changes.
[1] BFO Fix.  First, there was a problem with the BFO that I didn't notice until recently probably because I didn't use it very often: the BFO frequently wouldn't oscillate in LSB or USB modes.  I compared BFO voltages to those shown on the schematic & they were OK. I tried tweaking the bias with only slight improvement.  Next I tried installing a 1K resistor between the +11V common & the junction of R484 & R508 so that the BFO [& product detector] receive partial power while the radio's operating in AM but this didn't help much either.  Finally, it occurred to me that the 7.5-7.6-volt BFO supply after zener diode D429 & R508 might be a little low for stable operation so I replaced D429 with a 1N4739 [or NTE139A], 9-volt zener.  Now, the BFO seems to work great after recalibration.  I'm attaching a sketch showing these & other changes but, if anyone has a BFO problem, start by replacing D429.
[2] AGC.  I also added an RF amp stage which I'll cover shortly but the extra gain from it causes overload because the AGC circuit as designed, & even after my earlier changes, can't compensate enough.  This is because the signal from the detector diodes, D415 & D416 grows more negative [with respect to ground] as the signal strength increases & is applied to the inverting input of the AGC amp, U407.  However U407 is fed from a single-ended [11VDC] power supply so its output can't respond to an input going negative beyond zero volts; instead the output jumps to about 10.5 volts & shuts down the [second IF amp, U403].  I thought of two ways to correct this; first, basically is to reverse the polarity of the detector diodes, D415 & D416, & swap the signals to the inverting & non-inverting inputs of U407.  I chose not to do this because of the daunting logistics of extensive PC board mods.  The other way is to add about 3VDC of bias to the inverting input of U407 & increase the voltage to its non-inverting input so as to approximately equal or balance the two with no RF signal present.  That way even the strongest signals will never drive U407's inverting input to zero volts but will allow the inverting input to always track the signal from the detector.  I didn't want to use batteries for the 3-volt bias supply to U407's inverting input because of the hassle of replacing them.  Instead I added another secondary winding to the power transformer, T1.  I found just enough space between the doughnut or winding package & the two outside "posts" or end legs of the core for 30-gage kynar or PVC-insulated [wire wrap] wire.  Each turn of wire yields about 0.06 VAC so, ideally, there should be about 50 turns of wire, 25 on each end, connected in in phase so as to produce about 3 VAC.  This new secondary winding is then connected to a diode bridge made from Schottky diodes to minimize forward voltage drop across them.  If there isn't enough room to add all 50 turns to the transformer then put on as many as possible; the AGC action will be controlled by a user-accessible pot.  Also note the 3.3V zener across the DC output from the diode bridge; its purpose is to regulate the bias voltage to the inverting input as is the zener on the non-inverting input circuit so a momentary AC supply voltage change won't cause the input signal to temporarily overload or disappear.  Notice there's no current limiting resistor between the bridge & the zener; none's needed here because of the resistance from the inefficient magnetic coupling to the added secondary winding.  While this works great there's one more thing to point out: adding this new secondary winding to the AGC circuit precludes this radio from being 12-volt battery-powered without using a 12VDC to 120VAC inverter.  I made the bias voltage to U407's non-inverting input adjustable by means of a 100K potentiometer which I mounted on a bracket or panel on the back of the radio facing the front.  I made the mounting panel wide enough to accommodate additional controls.  Since the SW-7800 has no switch to disable the AGC for weak stations this pot is handy for setting the AGC level for both strong & DX signals.
 
[Due to size limits on postings the remainder of this article will appear in my next post.]