#27 Font \tt is more condensed in PDF than in PS

[HoHonza]

When I compile the following file on machine A (with
Linux Fedora Core 3: tetex-2.0.2-21,
tetex-dvips-2.0.2-21, ghostscript-7.07-33) I get extra
space after swiss, ababa in PDF. In PostScript it is
OK. The space is caused by moving letters closer when
transforming it to PDF. Wrong font selection for \tt in
prosper.cls?

When I compile the same file on machine B (with Linux
Fedora Core 2: tetex-2.0.2-13, tetex-dvips-2.0.2-13,
ghostscript-7.07-25) it works OK in both PDF and PS.

The error is PDF displayer independent. How should I
avoid the error?

\documentclass[pdf,default,slideBW,colorBG]{prosper}
% latex prosper-verb.tex
% dvips -Ppdf prosper-verb
% ps2pdf prosper-verb.ps
\begin{document}

\begin{slide}{Verb/Verbatim}

\verb|swiss|ccc

\verb*|swiss ab|ccc

\texttt{ababa}, $L=1$

\end{slide}

\end{document}