[Amps] Ameritron AL-1200

[TexasRF at aol.com]

Sounds like eight new capacitors and eight new bleeder resistors would take  
care of the immediate problem. After multiple failures there is a likelihood  
that the remaining capacitors have been stressed enough that their days are  
numbered.
 
73,
Gerald K5GW
 
 
In a message dated 10/30/2007 1:00:43 P.M. Central Daylight Time,  
km1h at jeremy.mv.com writes:

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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