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Well, the VFO rebuild did not work!

After putting all back together, the VFO was inoperative. But now it is working, and the fix will astound you or should I say the implementation will give you cause to say," I'll be damned!"

First, we must acknowledge something about Germanium transistors, like the 2N2092, which is that it is 65 years old. These class of transistors are prone to failure especially one which has a 4th wire ground lead that is internally connected to the transistor substrate.


2N2092 and 2N2093 are Equivalent PNP Devices
 L to R: Collector, Shield, Base and Emitter




I asked Copilot AI "What's up with Germanium Transistors" that fail?

 Common Failure Mechanisms

  • Tin Whisker Growth Tiny conductive filaments called tin whiskers can grow inside the transistor casing, especially if the interior is tin-coated. These whiskers can cause internal shorts between the transistor terminals, leading to erratic behavior or complete failure.

  • Internal Shorting Some vintage germanium transistors—especially those with built-in substrate grounds—are known to suffer from internal shorting over time. This is often due to poor sealing or contamination during manufacturing.

  • Thermal Sensitivity Germanium is more sensitive to temperature fluctuations than silicon. Heat stress or rapid thermal cycling can degrade the junctions, especially if the substrate ground doesn’t provide adequate thermal dissipation.

  • Voltage Spikes & Breakdown Without proper input/output protection, transient voltage spikes can damage the base-emitter junction. Substrate-grounded designs may lack sufficient isolation, making them more vulnerable to such stress.

  • Aging & Shelf Life Many germanium transistors are decades old. Even unused ones can degrade due to oxidation, moisture ingress, or breakdown of internal seals. Substrate-grounded types are particularly susceptible if the grounding path allows leakage currents or corrosion.

The Internal Shorting and Aging/Shelf Life are the main two culprits. Essentially, this time I saw no voltage on the collector because internally the innards of the 2N2092 were shorted to ground.

Others who are working with the same Project X rig told me about this solution and based on prior work, I felt it would work.

Recall that I tested the pulled 2N2092 in a transistor tester and then plugged it into a working radio. It passed both tests. But in those two cases I only used the Emitter, Base and Collector leads and ignored the substrate Ground Shield. There it was right before me... the answer.
 
I was able to get my nippers down into the VFO chassis and simply cut the ground lead on the 2N2092. Boom we have oscillation.

Them that know can make things go.

So now you know several pieces of critical information. Avoid vintage Germanium transistors especially those with 4 leads. When servicing an old boat anchor with 4 lead Germanium transistors try cutting the shield lead and see if that fixes the issue. Finally, a significant warning to me personally... Stop buying boat anchors!

73's
Pete N6QW


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