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[AMPS] that Alpha 77 is now working.

To: <>
Subject: [AMPS] that Alpha 77 is now working.
From: (2)
Date: Wed, 25 Jul 2001 03:26:16 -0700
>Some of you might remember my post about the 
>Alpha amplifier with the oddball tune-up problem. 
>Bill reports back in with the answer and the 
>problem found. 
>[cut and paste] 
To: <>
>Date: Wed, 11 Jul 2001 15:13:40 -0400
>From: Bob Sullivan 
>Subject: RE: Alpha 77 
>This was the A77 that had very low power out on all bands with a very
>shallow plate dip. So, for example, at 30w drive with 150ma grid current
>plate might dip to 750ma with power out around 100-150w. All bands tuned
>right on the money per the manual (tune and load) in a dummy load. There
>were LOTS of suggestions - bad relays, bad metering circuits, bad input
>circuit, bad bias, bad tuning network (miswired), bad torroids, bad
>caps, etc. 
>Many suggestions didn't make sense based on the "correct" tuning
>points. I carefully checked bias voltage and the output network and
>bandswitch for wiring errors, bypassed the output vacuum relay, replaced
>coupling caps, monitored bias during operation - all this checked good. I
>never suspected the vacuum variable tuning cap since the amp "tuned"
>So the capacitance must have been correct. Finally - in desperation 
>I replaced the vac variable (no small task) and, voila!, everything
>works. I
>have NO idea what is wrong with the capacitor except to note that
>you can "see" through them but this one is completely opaque with a color
>you see when a tube getter is flashed.
>Regards and 73,
>Bob W0YVA

/\  This is why folks who repair amplifiers need a high-potential 
breakdown tester a.k.a. "hi-pot".  I've tested new, unused, in the 
factory box units that broke down at low voltages.  Slight imperfections 
in the seal only show up with the passage of time. 


-  R. L. Measures, 805.386.3734,AG6K,  

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