Russian SI-180G (СИ-180Г) tube

I know this thread is a few months old but I thought I would do some digging on this. Turns out there is very little info out there for this tube, even on the Russian sites. I have looked over both suppliers of this tube and some Russian forums (with the help of google) and below are the only snippets of info I could find. I have put the findings from each result in a separate quote box.
It appears that this tube is beta sensitive, so not sure how that would pan out as a gamma background monitor. The last bit of info shows what someone calculated as a conversion factor by using the known conversion factors of other tubes. From what I understand of quite a lengthy Russian forum post this was calculated for background counts only and no actual isotope source was used, so take this as you will.

Technical characteristics
Geiger-Muller SI-180G (SI180G, SI-180-D, SI 180 F, SI180-T, T SI180, SI 180g)
Geiger-Muller SR-180g is designed for measurement of soft beta-radiation for wide application in the field of radiation control.

Russian military NOS Geiger Tube SI180G for ionizing radiation detection. Can detect gamma radiation. The tube has good sensitivity for natural background. 
Working Voltage: 380V-480V
Capacitance: 10pF

SI-180G - Very sensitive to background (84 CPM) but less to other sources. This might be the best tube I have for background. (I like the way it looks too.) However it's similar to the SI-29G on the other samples. A user (Justin) said that a CPM to uSv/h rate of 321 gave a similar uSv/h as his GammaScout. (I solder the wires to it like this.) 10/12/21 - Another user found  a conversion factor of 575 was closer to a calibrated measurement..

This GM counter tube offers about 2-3 times better sensitivity than the SBM-20 due to its larger diameter.

Specification:
Operating voltage: 360 - 420V
Initial voltage: 290 - 330V
Plateau length: 100V
Plateau slope: 0.1% / 1V
Capacitance between the electrodes: 10pF
Resistance at load: 5 - 10 MOhms
Operating temperature range: -500 +700
Length: 100mm
Diameter: 18mm

1) For those who are interested in the interpretation of the values, the following table is used for the calculation. (Jin highlighted my version.)

Tube values ​​imp/min in µSv/h:
SBM-20 0.0057
SBM-19 0.0021
SI-29BG 0.0082
SI-180G 0.0031
LND-712 0.0081
SBT11-A 0.0031
SBT-9 0.0117

And that is about all I could find on the internet regarding this tube. Quite a mystery. I would have thought there be some old datasheet out there, even is just a picture of it or something, but apparently not. One thing that came up a couple of times in Russian forums was the need for a large value anode resistor. 22M ohm came up a couple of times and using less than 3M ohm was detrimental to the use.
At some point I may try and get my hands on one of these and try and calculate the conversion factor based on different tubes and different isotopes. I think I have enough different sources now to be able to accomplish this with at least some accuracy and after exhausting the information out there, I think this may be the only way.