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Re: [Amps] Alpha 77 start up

To: "Jan Ditzian" <>
Subject: Re: [Amps] Alpha 77 start up
From: "Paul Christensen" <>
Date: Sun, 20 Feb 2011 20:33:01 -0500
List-post: <">>
The CW/LOW light should only come on when depressed after the 3-minute timer 
activation.  The light cannot activate without the 3-minute timer working. 
Also, it should not immediately come on when depressed if the amp is off --  
only after the 3-minute wait.

Check to ensure that the "READY" lamp is good and hasn't burned out.   It 
sounds like the 24V supply is fine.  I would next check with Glenn at Alpha 
concerning information on the CB-2A schematic.  It's probably not too 
different than the prior version.

Paul, W9AC

----- Original Message ----- 
From: "Jan Ditzian" <>
To: "Paul Christensen" <>
Cc: <>
Sent: Sunday, February 20, 2011 7:39 PM
Subject: Re: [Amps] Alpha 77 start up

> Paul,
> I note that the light on the CW/Low button came on when I pressed that 
> button.  Also, one of the meters is lit.   If I am reading things right, 
> all bulbs are 28 VDC, so I expect that the 24 volt supply is OK.
> I looked over the original Operating and Technical Manual, and there is a 
> handwritten note on Fig 21, the CB2 board, that this unit has the CB-2A 
> board.  There are other cryptic notes, but there is no specific change to 
> the schematic.  I have no idea where to find a CB-2A schematic.
> I will see if I can contact my friend with the test bench and a 24-volt 
> supply.
> Thank you,
> Jan, KX2A
> On 02/19/2011 02:29 PM, Paul Christensen wrote:
>> Jan,
>> The problem appears to be isolated to the three-minute warm-up timer. 
>> You're seeing 2600V which is correct while the three-minute  timer is 
>> activating.
>> First, measure the +24 VDC supply voltage.  It should be fine since you 
>> don't seem to be blowing the step-start fuse.  That would render the amp 
>> completely dead after the step-start resistors finally blew and threw 
>> shrapnel all over the inside of the amp.
>> The timer circuit is on circuit board CB-2 and is very simple in 
>> operation. Upon sensing +24VDC, C207 (22 uF) begins charging through R222 
>> (10 meg). This in turn activates SCR Q207, which simultaneously switches 
>> a more robust SCR Q208.  Q208 fire and pulls in relay K202.  Once K202's 
>> contacts close, +24VDC is supplied to the "READY" lamp (and other amp 
>> circuits) and the amp is ready to make power.
>> CB-2 unplugs from an edge-card connector so you can safely do some 
>> troubleshooting outside of the amp -- If you have an adjustable +24VDC 
>> bench supply, use it for testing.  Otherwise, be extremely careful when 
>> testing components in the amp.  CB-2 is not far from the HV contact 
>> points.
>> As W8JI once said, he's never had to troubleshoot an amp with AC power 
>> applied.  He's right.  It may take longer, but it's a much safer way to 
>> diagnose a root problem.  If you've ever diagnosed an amp problem by 
>> yourself, now is not the time top learn on your own.  Get on-site help if 
>> you cannot work on CB-2 outside the amp.
>> Paul, W9AC.
>> .
>> ----- Original Message ----- From: "Jan Ditzian" <>
>> To: <>
>> Sent: Friday, February 18, 2011 10:59 AM
>> Subject: [Amps] Alpha 77 start up
>>> I just received an Alpha 77 Dx, modified as a two-holer, as a gift (I
>>> have very understanding friends).  However, it came with a problem--it
>>> does not work. The startup light does not come on.  The previous owner
>>> sent a board back to Alpha to fix this problem, and their paperwork
>>> shows that they repaired it and then tested it in an Alpha 77Sx, which
>>> is equivalent to the two-hole modified Dx, and it worked.  However,
>>> after putting the board into this rig, the problem remains.  Since I am
>>> new to this amp, and did not have it integrated into my station, I did
>>> the following checks:
>>> I set up the amp with no exciter, but with power, and the fan comes on
>>> and the voltage goes to about 2600 volts. I followed the regular startup
>>> procedure and, sure enough, the light does not come on after six minutes
>>> (it is supposed to take about 3minutes).  I then put a cable into the
>>> relay jack on the back, repeated the above process, went ahead and put
>>> the amp into CW/low power mode after a six-minute wait, and then shorted
>>> the relay cable.  I did not hear a relay click--nothing happened.
>>> Can someone help me to isolate the problem with this amp?  Until this
>>> happened, the previous owner (the donor of the amp) was using it without
>>> a problem.  There was no cataclysmic event that preceded the failure to
>>> start up.
>>> I can imagine problems like bad contacts on the board connector, or
>>> perhaps the failure of another relay somewhere.
>>> Thank you,
>>> Jan, KX2A
>>> _______________________________________________
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