[Amps] Ameritron AL-1200

[jeremy-ca]

There are those who would have you believe that Ameritron used a special 
capacitor not available to us common folk. I have no idea if it is true but 
I suggest that you call Ameritron and dont rest until you are put in touch 
with someone who is in the position to answer.

Carl
KM1H



----- Original Message ----- 
From: <n9bx at mchsi.com>
To: <Amps at contesting.com>
Sent: Tuesday, October 30, 2007 1:03 PM
Subject: [Amps] Ameritron AL-1200


> Hi:  I have a perculiar problem with the high voltage power supply on the 
> AL-1200.  Here is the sequence of events.
>
> I had the Amplifier on and it was idling and all of a sudden it crackled, 
> stopped and about 15 minutes later did this again.  High Voltage stayed 
> the same ,(meter Indicates 3600-3700 VDC,  The whole time.  Well I shut it 
> down and after the HV was alowed to bleed off I started checking the 
> filter cpacitors.  this amp used 210 MFD at 450 VDC and Had eight of them. 
> Yes I know that 8X450 =3600 Volts, and that's about what my voltage reads 
> on the meter but I figured the designers of this Amp knew what they were 
> doing and there was an adequate safety margin built in.
>
> Well One of the Capacitors was Bad.  In fact the little white Dot that is 
> on the Capacitor was bubled up and the Capacitor did not charge or 
> discharge.  I then checked all of the 50K ohms 7 watt resistors across the 
> Caps and sure enough two of them read open.  These were the ones that were 
> across this Cap and the one Adjesent to it.
>
> So I replaced the Resistors, This Time with 75K OHM Flame proof Resistors, 
> all Eight of them with the same wattage and replaced all Eight 
> Electrolotyic Capacitors, all I had were 220MFD at 450VDC so Hey A little 
> bit more voltage regulation key down but not that much.
>
> Turned the unit back on  Everything was fine.  Made one QSO, Voltage was 
> above 3600 VDC again as before and I thought the Amp was back in Business. 
> Well after sitting with no load on it two hours it started crackling 
> Again, and one again it does this at about the 15 minute interval.
>
> I am almost sure that I will find the same Bad components agin, but What 
> is causing the Capacitors, Or more likely the equalizing resistors to fail 
> which causes the Caps to Fail.
>
> Sorry for the Bandwidth but this amp has been in service for 12 Years with 
> not a hint of Problems before This Started to Happen.
>
> 73 Bruce N9BX
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