[jshorva65]

With regard to hiding an SBE "Orange Drop" or Mallory "150-series" cap in the old paper shell, I don't recommend it unless a material other than wax but with similar appearance and superior sealing properties is used to "pot" the thing. Remember that a less-severe form of the same problem that "killed" the wax caps will eventually return if wax is used as potting material for the new caps. What happens is that the wax absorbs moisture from the surrounding air and any impurities that the water vapor may contain. Eventually, that moisture-laden wax (even in a "stuffed" cap, it's still touching the leads) begins to act as a resistance in parallel with the capacitor inside. The elimination of the paper dielectric limits how low the leakage resistance can go for the "stuffed" cap, but even a megohm of unwanted DC resistance across a capacitor can change its behavior in the circuit enough to impair overall performance.

Although I doubt that a "stuffed" cap is likely to short and "pop" as some (particularly AC line or screen grid bypass) paper caps were known to do, leaky coupling caps in a video amplifier make for an awfully crummy picture and may cause tubes to wear more quickly than normal due to running at a higher bias point. The change in the slope of the circuits' "DC Load Lines" from what the engineers had intended them to be can cause anything from distortion of signal waveforms to reduction of tubes' life expectancies.

Consider a two-stage RC-coupled amplifier using cathode-resistor bias. Normally, the coupling capacitor should pass the AC component of the signal while isolating the vastly-dissimilar DC levels of plate and grid circuits. If we introduce unwanted DC resistance into the model in parallel with the coupling cap, we now have a voltage divider fed by B+ through the preceding stage's plate load and the capacitor's leakage resistance with its "output" dropped across the grid resistor of the following stage. The result will be that the grid will be biased to a potential more positive than normal and the tube will draw more cathode current than under normal conditions.

For two halves of a 6SL7, 6EU7, 12AX7 or similar high-mu triodes as V1 and V2 in a two-stage audio amp, let's assume B+ as 300V, plate loads of 100K, grid resistors of 470K, cathode bias resistors of 1.5K, quiescent plate currents of 1.5mA, quiescent plate dissipations of 225mW and 0.022uF coupling capacitors (a very common circuit in guitar amps, but also a great generic two-stage RC-coupled amplifier circuit example). All voltages referenced to "ground" or B-. Grid voltages should normally be 0V, and we would observe about +150V at each plate and +2.25V at each cathode. If interstage coupling capacitor C2 developed a leakage resistance of 1M, things would change slightly in the first stage, but drastically in the second. The leakage and the second-stage grid resistor would become a DC voltage divider so the DC level of the grid of the second stage would become 1/3 the voltage at the plate of the first stage (150V*0.5M/1.5M=+50V). The second triode would wear very quickly and the plate and cathode resistors will almost certainly overheat and drift in value. For this example, the effect on the first stage of the 1M resistance of C2's leakage in series with R4 as an additional 1.5M DC load resistance is less than 10%. The effect on the circuit of V2, however, would be significant even if C2's leakage resistance were 10 times greater (10M). For this condition, we find that the grid voltage for V2 becomes 150V(0.5M/10.5M)=+7V.