[Hammarlund] vibrating hum on sp600?

[Roy Morgan]

At 12:03 PM 3/31/2005, you wrote:
>Hello all,
>
>Just received my GenRad 1001A rf generator and have been starting to learn 
>about how radios work and how to use test equipment with them.  Had a question.
>
>When I turn on my sp600 with the rf and af gain set to "0" I can hear an 
>audible hum coming from either the big transformer or the shorter one 
>right next to it,

Eugene,

You *may* have an obscure problem with the filter choke. Normally these 
transofrmers don't hum much.

If the insulation in the filter choke is leaking electrically there will be 
a heavy load on the power transformer and rectifier.. To test for this, 
pull the rectifier tube out and see if the hum goes away.

One very ill-advised "fix" for this is to insulate the choke from the 
chassis..DO NOT DO THIS.. it is very dangerous to you and other folks who 
may own the radio after you do.

Also, the transformer has a higher voltage tap that you should use to 
reduce the B+ and filament voltages in the radio.  Check the schematic.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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