[Drake] L7 and L4 PSU

[W4AWM@aol.com]

<<When running an L7 amp (with L-7 PSU)=A0 in the "SSB" position there's a
*very* loud BUZZZZ from the transformer after about 20 minutes or so.>>

Hi Steve,

As far as I can tell, the power supplies are identical and I have both units=
=20
here.

Since there is no problem with the L-4 PS, that eliminates any problem in th=
e=20
amplifier.

I believe what you are experiencing is loose laminations in the transformer.=
=20
When the transformer heats up, the heat generated causes the laminations to=20
expand and the hum disappears since everything is nice and snug. You might t=
ry=20
tightening up the hardware on the tranny frames. That may solve the problem.=
 =20
If you haven't checked the filters lately, now is a good time to do that whi=
le=20
everything is apart.

SAFETY FIRST:  Be sure to disconnect the power supply from the AC line and=20
discharge the caps before getting in there with your bare hands.

Good luck and please post your findings so that all may learn from your=20
experience.

73,

John,  W4AWM


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