[R-390] Motorboating on R-390A

[Bob Camp]

Hi

Does the calibrator work correctly when it is switched on?

Does the problem go away when you pull out the first RF amplifier tube?

If the calibrator is working properly then this isn't the 
multi-vibrator in the calibrator circuit getting goofed up.

If the is still there with the RF tube gone then it is coming from 
inside the radio. Otherwise this sounds a lot like a problem external 
to the radio.

	Take Care!

		Bob Camp
		KB8TQ


On Jan 22, 2005, at 11:34 AM, R390rcvr at aol.com wrote:

> Good day all:
>
> Nice weather here in Michigan, about 12" of snow, and soon to be 30 mph
> winds!
>
> I just put a Motorola R-390A up on my bench for the first time. The 
> first
> sympton that popped up was   motorboating on all bands.   It occurs 
> every 70-75
> KC, like clockwork. In some cases, it is louder with the BFO on. It 
> disappears
> with the antenna disconnected. The motorboating is 5-7KC wide, with a 
> slight
> peak in strength centrally. I have subbed every tube except the 
> rectifiers,
> 3TF7 and OA2 without any effect. If there is a very strong signal, it 
> isn't very
> noticeable, but in quieter areas of the band, its is quite loud. I 
> haven't
> found any switch settings that effect it at all, except, not present 
> in Calibrate
> setting.
>
> I would appreciate any thoughts you might have.
>
> Thanks. I will be out shoveling for a while!
>
> Randy Stout
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