[Engineer]

choobs wrote:
Pulled the amp from an old phono player. It was intended to be mounted
with the tubes horizontally. I want to situate it vertically. When I
do so I get a lot of hum. If I turn it upright, the way they intended,
it's much quieter. Can someone explain why this might be? Can I unbolt
the power transformer and rotate it 90 degrees? Thanks to all.

This may have no relevance to your problem but I once had a pre-amp (a
WA-P2) on the bench (out if it's box) that hummed at 120 Hz in some
positions and not in others. I chased all sorts of filter connections
and inductive sources to no avail, then realized that it only hummed
when the high gain tube was illuminated by the flourescent lamp over
the bench! Problem solved - put on the tube shield (which I'd left
off) and put it back in it's box.
Cheers,
Roger

[Bob H.]

Mabye a filament lead has sagged inside of one of the tubes over time,
and righting it has produced the hum. Tried pulling the tubes, etc?

Bob H.


choobs wrote:
On 6 Aug 2006 15:41:41 -0700, "Engineer"
wrote:


choobs wrote:
Pulled the amp from an old phono player. It was intended to be mounted
with the tubes horizontally. I want to situate it vertically. When I
do so I get a lot of hum. If I turn it upright, the way they intended,
it's much quieter. Can someone explain why this might be? Can I unbolt
the power transformer and rotate it 90 degrees? Thanks to all.

This may have no relevance to your problem but I once had a pre-amp (a
WA-P2) on the bench (out if it's box) that hummed at 120 Hz in some
positions and not in others. I chased all sorts of filter connections
and inductive sources to no avail, then realized that it only hummed
when the high gain tube was illuminated by the flourescent lamp over
the bench! Problem solved - put on the tube shield (which I'd left
off) and put it back in it's box.
Cheers,
Roger

No, it's not the bench light but that got me thinking. I did change to
a stand-off approach to the heater string and that got rid of 90% hum
in the manufacturers intended position- like they had it mounted in a
giant piece of furniture- the actual unit is about 5x7x2 inches max.
It still hums like crazy if I stand it normally on a table top.
I will hook up just a turntable instead of a CD player and see if the
input impedance (not sure what that is really but it sounds important)
is part of the problem.
Also, the only speakers I have are 8 ohm and I wonder if the console
had 4 ohm speakers.
Thanks, everyone and keep tinkering.