[Boatanchors] VC radio tube questions

[J. Forster]

Some time ago Bill Howard was asking some questions about reproducing a captured
VC radio. Since then, we've been working together on reverse engineering the set
he has. There is some question about whether the set has the correct tubes in it
now.

A brief set description:  The set is basically a 5 tube superhet. The first tube
is a pentagrid converter. There is no RF amplifier preceding it. The LO is uses
a three winding air core coil. The primary is bifilar wound in the filament
circuit, the secondary is parallel tuned tank (tuned by a section of the main
tuning capacitor). The RF input is from a 1:4 step-up air core transformer, the
secondary of which is another parallel tank, tuned by the other section of the
main tuning capacitor.

The IF is composed of two 1L4 tubes and three double tuned circuits. Each IF
tuned circuit is composed of two cored coils, each resonated by an external
capacitor. Coupling is via a small capacitor, bridging the input tank to the
output tank. The result is an IF coupling network of LC - C - LC.

The output of the last IF goes to the diode plate of a 1S5, the other part of
which acts as a gain stage. The audio output is capacitively coupled to a
pentode output stage and a filament (most likely) transformer used as an output
transformer. The final tube is either a BFO or some variety of noise blanker,
but the circuit is unclear at the moment.

The questions:

In the first stage, the tube appears to be a 1R5, except that a 1R5 has pin 5
internally tied to pin 1. In the circuit, pin 5 is tied to a decoupled b+
through a 15K resistor and a 0.2 MFD bypass capacitor to ground. Does anyone
know of another tube, similar in most respects to a 1R5, but which would likely
use a decoupled B+ to pin 5?

The next question is similar, but concerns the output stage. It is clearly
supposed to be a pentode, with the screen on pin 4, connected to B+ through a 22
K resistor. So, does anyone know of a tube like a 1L4, but with the following
pinout:

1 & 5 tied, Filament
2  Plate
3  G1
4  Screen
6  G2 ??
7  Filament

It IS possible that the correct tubes may NOT be US types. They could be Chinese
or Russian  or their variants of US types.

Thanks,
-John