[Amps] Alpha 76a

[Jeff Blaine]

I just replaced my caps in a 76pa.  HV slid down over the last month and I was busy on other things and had not noticed it till it 
was time to rock and roll.

Upon visual, the caps "looked" fine as well.

On the meter, 4 showed roughly 210 uF.  1 showed 50 uF and 1 showed no indication on the meter.  I did not test further.

Replaced the caps and it's back in fine action.

73, Jeff ACØC
www.ac0c.com

-----Original Message----- 
From: ROBERT HARMON
Sent: Monday, September 12, 2011 6:20 PM
To: amps at contesting.com
Subject: Re: [Amps] Alpha 76a

Colin,

I didn't check the caps in my 76, I didn't see any evidence of swelling or leaking when I visually inspected them
but since they were original I thought it would be prudent to replace them.
HV electrolytics have a life span of between 15-20yrs.  They quit producing the Alpha 76 series in 1985 so the original
76 series HV filter caps are at least 26 years old.
They probably would have lasted longer before failing but I felt it was good preventive maintenance.
Replacing the cap bank is pretty easy.  RF Parts has the original replacements.

Another PM item worth doing is lubing the fan.  The 76 fan has a sleeve bearing and a little lube will extend the life
and prevent the fan from getting noisy and needing replacement down the road.  (The original fans are no longer available.)
Remove the motor end cover and do several repeated applications of fine machine oil like 3 in one oil.  The shaft bearing is
a porous bronze alloy and will soak up a substantial amount of oil.  The motor end cover has an o-ring seal to prevent any oil from
leaking out.

Bob
K6UJ




On Sep 12, 2011, at 1:43 PM, Colin Lamb wrote:

> "One thing you might consider if you haven't already is replacing the power supply HV filter caps.  They are more than ready One 
> thing you might consider if you haven't already is replacing the power supply HV filter caps."
>
> Two weeks ago, I had my Alpha 76A apart and decided to check out the electrolytics and bleeder resistors.  I removed each 
> capacitor and checked them with a capacitance meter and and ESR meter.  I also measured the leakage current under load.  The amp 
> had not been used for years, but after forming for a few minutes, the leakage current dropped to almost nothing.  Measured 
> capacitance was within a couple percent.
>
> These caps are high quality original caps and did not need replacement.  Although I have found other amps that needed replacement 
> caps, the Alphas have held up well.  Worthwhile to try them before replacement.
>
> 73,  Colin  K7FM
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