In the US, there are no exemptions that I am aware of for Tow Planes.
14CFR 91.215 applies. It is rather extensive.
91.215 (b) All aircraft in airspace described in (b)(1) through (b)(5) must
have Mode 3A, C or Mode S.
(b)(1) All aircraft in Class A, B or C
(b)(2) All aircraft within 30nm of Appdx D airports .. (Mode C Veil) up to
10,000MSL
(b)(3) starts the exemptions..
(b)(4) above the ceiling of Class B, Class C up to 10,000MSL
(b)(5) All aircraft (except gliders, balloons, no electrical power).. etc
(b)(5)(I) above 10,000MSL

Bottom line, any aircraft , outside of 30nm from a "Class B airport" and
below 10,000MSL (or 2500AGL if higher) would not need a transponder.
A tow plane is not exempt just because it is towing.

If any aircraft flying more than 30nm from a Class B airport and outside of
Class C airspace, and stays below 10K, no transponder required.

"Andy" wrote in message
...
Worldwide, what exemptions from transponder equipage apply to glider
tow planes (assuming built and certified with an electrical system)?.

How typical is it that tow planes are not equipped with a mode C or
mode S transponder?

Andy