Is the transformer firmly and securely mounted and grounded? Perhaps adding
MOV's to the primary.
73, Roger
W7TZ
CN83ia
Grid Busters
w7tz.webs.com
On Mon, Sep 4, 2017 at 3:27 PM, Ron Youvan <ka4inm@gmail.com> wrote:
> Roger VE3ZI Parsons via Amps wrote:
>
> I recently 'completed' a new amplifier. Everything seemed fine and I was
>> quite happy. But I was only checking the transmit functions.
>>
>
> However: I now find that when I power on the HV I get rf noise in the
>> receiver - sounds and spectrum are just like power line arcing. But it's
>> not.
>>
>
> Obviously the first suspect was the high voltage circuitry. I disconnected
>> the wiring to the tube, followed by the capacitor bank and bleeder
>> resistors, followed by the rectifier diodes. No difference.
>>
>
> So it seemed I was left with the power transformer. With AC power on the
>> primary and nothing on the secondary I get the noise. I tried an RFI filter
>> in series and it fixed it completely. However, I am not very keen on
>> leaving that in circuit because it seems to be covering the real fault. I
>> then tried connecting the power transformer primary directly to the circuit
>> breaker (no secondary load). No noise. I then connected the power
>> transformer directly to the circuit breaker (again no secondary load), but
>> reconnected the soft start, etc (That wiring going nowhere). No noise. (I
>> can't connect the primary of the HV transformer directly to the circuit
>> breaker with a secondary load as I need the soft start in that condition.)
>>
>
> (The HV transformer is new and very well impregnated. It does not get hot
>> or let smoke out. I find it difficult to believe that there is something
>> like a shorted turn causing the noise, but I suppose it is possible.)
>>
>
> OK, I thought. Perhaps it's a bad contact in the soft start relay or the
>> HV relay. Cleaned the contacts up (they actually looked fine before anyway)
>> and no difference to the noise. Bypassed everything I could find. No
>> difference.
>>
>
> Last thing. The noise only happens when the transformer has AC power. Once
>> the power is off, the noise disappers even before the capacitor bank has
>> discharged.
>>
>
> Obviously I'm missing something! Any ideas what?
>>
>
> This sounds (pin intended) like you are hearing the tubes (idling)
> electron flow, check your T/R switch and it's connections.
> --
> Ron KA4INM - Youvan's corollary:
> Every action results in unwanted side effects.
>
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>
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