[Milsurplus] [ARC5] Addenndum: TU-4 vs. B-29 Radio Sets

[Mike Morrow]

Meir wrote:

> The extra tube in the US-9 is an octal VR type tube (Russian tube nomenclature
> SG-2S, 72 V firing voltage) for regulating the local oscillator voltage. A much
> better solution than the 991 neon bulb...

The early US-9 is electrically and mechanically essentially identical to the
BC-248-H/K/L/R model.  It is pictured inside and out, with schematic, in my Tu-4
Radio Installation book of 1950.  There is definitely a 991, but it is shown in
the book as "Neon stabilizer type MN-7" (from the Russian text).

Ray wrote:

> The Russian US-9 also has a front panel mounted fuse and two different style
> headphone jacks to accommodate the ¼ inch western style connector or the two
> pin jack that most Russian radios used up to the seventies.

This is not true for the early US-9.  There is no panel-mounted fuse, nor is
there any audio connection for phone other than two jacks *identical* to those
on the BC-348-*.

I have found no electrical differences in the schematic of this early US-9
and the BC-348-H/K/L/R, except for the AF output tube.  For the BC-348-H/K/L/R
that is a 6K6.  My US-9 schematic shows this tube to be (in Cyrillic!) a 6V6,
which is odd because V is not Cyrillic.  Apparently a western-type 6V6 is used
in the output, and it hasn't been assigned the expected Cyrillic 6B6 designation.
Also, as a result of the greater 6V6 filament drain compared to a 6K6, the
value of the shunt resistor in the rest of the filament chain is lowered 
from 190 to 125 ohms.

So, to see a schematic of the early US-9, find a schematic of the BC-348-H/K/L/R
and make the two changes described in the paragraph above.

73,
Mike / KK5F