You can alternatively use AutoHotKey with this script. This isn't exactly a quiet way but it works. The shortcuts are Ctrl+Alt+= to increase the size, and Ctrl+Alt+- to decrease the size. If you want Ctrl +/- keys, just remove exclamation marks.
ChangeFontSize(Direction="Down") {
nIndex := 15;
WinGet, hWnd, ID, ahk_class PuTTY
hSysMenu := DllCall("GetSystemMenu", "UInt", hWnd, "UInt", False)
nID := DllCall("GetMenuItemID", "UInt", hSysMenu, "UInt", nIndex)
PostMessage, 0x112, nID, 0, , ahk_id %hWnd%
SendInput {Shift Down}{Tab}{Shift Up}a{LAlt Down}n{LAlt Up}{LAlt Down}s{LAlt Up}{%Direction%}{Enter}{LAlt Down}a{LAlt Up}
}
#IfWinActive ahk_class PuTTY
^!=::
ChangeFontSize()
return
#IfWinActive ahk_class PuTTY
^!-::
ChangeFontSize("Up")
return
This was tested only on Windows 8.1 using PuTTY 0.62 (the vanilla one from the primary website). You may have to adjust nIndex value, which is 0-based and includes dividers, if your system menu looks different from what I have. If you're using a different version of PuTTY or a derivative then you may also have change the sequence of shortcut keys in the script. Make it work and enjoy.
This is what my PuTTY system menu looks like: PuTTY system menu on Windows 8.1
You can do this in the default Cygwin terminal (mintty), which incidentally is based on bits of PuTTY. – ak2 – 2012-06-28T14:22:14.497