Reading the tea leaves which in a broad sense is observing the data and making a determined decision is so important. It took a while before discerning FBF (Feed Before Fun) was required with Mary Jo.
I wired up a power plug (hay wired is more like it) and did a bit of initial sleuthing with the HW-32A straight away from the storage location. The tubes light and I can hear a signal generator about 5 feet away but not physically connected. The signal is detected at maybe S5 but not like other radios (commercial and homebrew) where the S meter is pinned using the same approach.
I actually heard two stations but for the most part the receiver was deaf. This is a tea leaf moment, as the receiver system is not amplifying the signals from the antenna to the speaker. Don't rush over that point too quickly.
For many blog readers this is a BOB (Bordering On Boring) moment especially since we are dealing with Thermatron's. If you feel BOB'd you missed the memo. The real thrust at this point is a trouble shooting methodology which applies to any receiver whether tubes or the latest SDR.
Another critical piece of data from this initial test is that the receiver will actually do all of the steps in the block diagram --- but in one or several places not too well.
It seems like a functionality included in most transceivers of this vintage was the capability to use the transceivers with an outboard receiver. Check your old Drakes and even early Ten Tec's. The HW-32A as well has the capability. In the HW-32A scheme the antenna relay takes the signal at the antenna and routes it through a set of relay contacts and then on to a separate winding on L3 that has the main winding in the plate circuit of the 12BY7A Driver tube.
The connection point for the external receiver is AFTER the relay contact. So, if you connected an antenna at that RCA jack versus the external receiver you would be applying the antenna directly to the winding on L3. This is a test. Suppose the antenna relay contacts are bad then you would get little signal into the winding. But the test showed the same signal level with the antenna properly connected to the Coax connector or to the external receiver port. Scratch the Relay off the list as the issue.
Another noted anomaly and perhaps a 1st area to fully evaluate. At Power ON the S Meter pins and as the tubes warm up the S Meer drifts down to less than S1 as the atmospheric noise drives the low-level S Meter reading.
I see the same action with my Collins KWM-2. So that is a normal response. Now as you advance the VOLUME control the signal gets louder but then you hit a point where the background sound is loud, but the signal disappears, and the S Meter gets pinned like at Turn ON. Let's look at that portion of the schematic (Think AGC).
A 6EB8 is used as the Audio Pre-amp and Audio Amp stage. Pin 3 on the Triode section connects to the top end of the Volume control through a capacitor, a 5000pF (.005 Ufd). Also, off Pin 3 is a 220K Resistor in series with a 0.02 Ufd (20,000pF) Cap feeding the AGC circuit (the two diodes). The Caps and Resistors in the AGC circuitry set the attack time and decay times. The output of the AGC circuit goes to only one place --- The Receiver RF Amp Tube direct into the Grid of V8A, Pin 2.
Let's digest that for a moment. If we have an extremely strong signal that passes through the receiver system when it hits the triode section of the 6EB8 that signal (an AC type signal) it is rectified by the AGC to produce a NEGATIVE voltage whose level is proportional to the input. That negative voltage goes into V8A Pin 2 and reduces the RF amp stage gain.
Under normal circumstances this works pretty well. But the low recovered signal levels and the pinning of the S Meter when you full open the Volume control signals that the AGC is very much reducing the RF stage gain at low signals levels which it shouldn't to completely cutting off the RF amp tube and pinning the S Meter.
Well at least that is a starting place to wit if the 5000pF cap at Pin 3 to the volume control is shorted that certainly would impact what happens to the other components connected to Pin 3. The immediate argument contra to a shorted cap would be that DC is being pumped into Pin 7. But look closely as there is a 0.02Ufd cap off of the center wiper on the Volume control that would block the DC and the audio amp would still work.
This is the last posting on the HW-32A as we have hit the #3 gag level, and most blog readers are yawning at this point. But if you look deeply into the blog posting it is not about vacuum tubes but a trouble shooting process.
A brute force action on my part is to replace many of the components on the 6EB8 circuitry including the AGC part. This may not fully resolve the problem but certainly we can then scratch that off the list as possible issues just like the antenna relay.
I am hooked (more like an obsession now) on proceeding with the HW32A re-invention and so future blog postings will be more than a little light as I spend time on the rejuvenation.
Them that know can make things go.
Pope Leo for POTUS 48! Wow that would certainly rancor the separation of Church and State advocates. Just like letting the lions loose in the Colosseum, a real spectator sport.
73's
Pete N6QW