Hmm, 60 Hz, sounds lika bad tube. Perhaps a filament to grid or other tube
elements short? Try replacing the tube if cost permits.
Aloha, and Good Luck,
Ed Pagaduan
----- Original Message -----
From: John Hill <jhill@visi.com>
To: <amps@contesting.com>
Cc: <henry@contesting.com>
Sent: Wednesday, July 12, 2000 6:07 PM
Subject: [AMPS] Re: Power Supply problem
>
> Greetings again;
>
> Thanks to the multitudes who responded to my post. I learned
> a few things and appreciated the anecdotal as well as the
> technical feedback.
>
> In retrospect, I believe something else is contributing to my
> transmitted signal having what appears to be AC components
> on it. I say this because, as I mentioned, there is about 180
> volts of AC on the B+ of 3800V when idling at 100ma. That's
> 4.7% ripple. This is where it gets interesting. At 250 ma of
> plate current (drive applied) the ripple stays the same. At
> 500 ma of plate current, ditto. If a component were failing,
> I'd expect the ripple to increase as the current increased.
>
> Now, my curiousity has increased. I dug out my trusty
> Tektronix 454 oscilloscope and looked at the component
> using the metering take-off from the B+. Lo and behold,
> this is 60 Hz with some minor commutation in it. Why
> 60 Hz? This power supply is a full wave bridge, or at
> least it's supposed to be. It only gets odder from here.
> This AC component was only 50mv p-p through the
> metering divider network. Given the division factor
> of the network, that equates to 44VAC of ripple, or
> approximately 1.2% ripple on a 3800V line.
>
> The only means I have to evaluate the two rectifier
> arrays was to take a 30V power supply with a
> current limiting resistor and look at the voltage
> drop across each leg. They were 14.5V, 14.4V,
> 14.53V and 14.36V. Not even a junction difference
> between any of them assuming they're not Schotky
> devices. Allowing for silicon, they must have 20
> or so junctions in each leg.
>
> Several people asked similar questions. The exciter,
> an FT-1000D is clean by itself. The hum is there
> on CW with a continuous carrier. The final filter
> cap checked at 16uf (per spec) and almost no
> leakage on the Sencore. The B+ drops from a
> resting value of 4040V to 3820V under load. It
> does not drop much more than that from 100ma
> up to 800ma. The bleeder resistors (4x20k ohm)
> all get hot, so I assume they are working.
>
> I am seriously thinking along the lines of an AC
> loop somewhere.
>
> Thanks again to all of you.
> John, NJ0M
>
> Sent to amps and henry@contesting.com
>
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