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[Amps] Apparent Arcing

To: Amps <>
Subject: [Amps] Apparent Arcing
From: Roger Parsons via Amps <>
Reply-to: Roger Parsons <>
Date: Mon, 4 Sep 2017 20:25:19 +0000 (UTC)
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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?


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