On Sun, 25 Feb 2007 18:39:16 -0800, "Richard Knoppow"
wrote:

It is possible for the lamp itself to be producing the
buzz. Lamps sometimes do this when near the end of their
lives. That might also account for the variation in
brightness.


True.

To the OP:

If there is a variation in brightness, there will also be a
significant variation in colour temperature, which could significantly
affect results.

A new bulb may well effect a cure. Philips 13139, or 6604 if you have
the earlier bulb holder. The 6604 is hard to find and expensive.

Most Focomat V35 enlargers have been converted to take the later
Philips 13139 bulb, which is much easier to find and reasonably
priced, for example GBP 11.55 from:

http://www.bltdirect.com/products.ph...rent=7&cat=228

If you remove the protective plate over the rear of the enlarger head,
you will find the bulb type clearly marked.