From: Bendzh on
I did think of the transformer, but wouldn't the sound be coming from
there rather than the head in that case? Or maybe the fluctuating
current induces buzzing in the head?

From: Tony Polson on
On 25 Feb 2007 11:50:21 -0800, "Bendzh" <d.a.milligan(a)sms.ed.ac.uk>
wrote:
>I did think of the transformer, but wouldn't the sound be coming from
>there rather than the head in that case? Or maybe the fluctuating
>current induces buzzing in the head?


The current to the bulb is 12V AC (alternating current) so it is
capable of causing buzzing at 50Hz.


From: Richard Knoppow on

"Bendzh" <d.a.milligan(a)sms.ed.ac.uk> wrote in message
news:1172432799.822711.315660(a)h3g2000cwc.googlegroups.com...
> Slapping the head does nothing, and I have the lamp holder
> screwed in
> tight. The buzzing's continuous but gets softer and louder
> as the bulb
> is brighter and weaker.
>
Check the lamp itself and the condition of the contacts
in the holder. If the lamp socket or lamp base are corroded
they may have developed intermittant high resistance which
may also cause the buzzing. Of course, also check the
wiring.
A voltmeter will also be helpful in discovering if the
output of the transformer is varying around.
The source of the buzzing may be difficult to localize. A
makeshift stethescope will help. This can be no more than a
stick of wood or even a long pencil. Hold one end against
you ear and poke the other around where you think the sound
is coming from. Sometimes this will locate the source. Its
an old auto mechanic's trick.
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.


--
---
Richard Knoppow
Los Angeles, CA, USA
dickburk(a)ix.netcom.com



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From: Tony Polson on
On Sun, 25 Feb 2007 18:39:16 -0800, "Richard Knoppow"
<dickburk(a)ix.netcom.com> 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.php?products_Current=7&cat=228

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