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[AMPS] Alpha 76PA

To: <amps@contesting.com>
Subject: [AMPS] Alpha 76PA
From: measures@vc.net (Rich Measures)
Date: Fri, 23 Jan 98 01:34:26 -0800
>Hello all;
>
>I am in the process of repairing an Alpha 76PA for a friend. 
>
>From initial inspection, I have found the 2 resistors in the step-start (R1,
>R2) burned and the Plate choke burned in half. The owner states that the amp
>worked fine, took off the top cover to do some dust cleaning inside, and the
>dummy powered it up by holding the AC interlock switch on, failing to notice
>the high-voltage intelock mechanical switch !!!
>
>I would think (by studying the schematic) that the choke would not be affected
>by this act of stupidity, 
agreed.  
>but  i can understand the inrush ckt resistors
>going.  My conclusion is that he fried the plate choke befofe hand, then
>opened it up for inspection and then screwed up the step start ckt by failing
>to obvserve the hv safety mechanism. 
makes some sense
>Does anyone know if the plate choke is still available from Alpha, 
easy to rewind with wire from electric motor shops.  Bring ur own empty 
spool.  
> as well as
>a good source for the 10ohm/12w chassis-mountable reisistors ??
>
>My next thought is to check the 3 8874 tubes for a short. Any suggestions ??
 Over half of the kaput 8874s I see have gold sputtering damage.  Test 
with a high-pot. set to 2x the rated anode/plate v:   2.5kV*2= 5kV.  The 
leakage should be under 10uA. Perform the Funderberg gold-sputtering 
test.  Loose gold can damage the hv-rfc.   A small amount of loose gold 
can be resettled. 
 [see 'Amplifiers' at < www.vcnet.com/measures >]
cheers, Eric

R. L. Measures, 805-386-3734, AG6K   


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