[Amps] Alpha 78 Problem

[K8MLM at aol.com]

Properly adjusted the electronic bias works fine... no chop, no  splatter.  
I installed a pot to fine tune adjust mine.
 
Bob
K8MLM
 
 
In a message dated 12/29/2009 5:51:22 P.M. Eastern Standard Time,  
km1h at jeremy.mv.com writes:

When the  77 was still in regular use it was easy to spot one by the 
splatter 
caused  by the electronic bias spike. There has been a lot written about a  
fix.

Carl
KM1H


----- Original Message ----- 
From:  "Jim Barber" <audioguy at charter.net>
Cc:  <amps at contesting.com>
Sent: Tuesday, December 29, 2009 5:15  PM
Subject: Re: [Amps] Alpha 78 Problem


> Apologies for  hijacking the thread, but speaking of the Alpha 77 bias,
> is there a  preferred method for defeating the "active" part? I remember
> seeing  somewhere that some revs had a pot for adjusting it that could be
> put  at an extreme to continuously enable bias, but I don't believe
> either  of my 77's has that pot.
>
> Why do it? Probably not a good  reason, but I've been asked maybe 2000
> times "Are you running VOX?" -  I get tired of explaining how the active
> bias circuit in my amplifier  would make it seem so. Unless the cooling
> system is otherwise  inadequate, (and I don't believe it is) I'd rather
> just be done with  it.
>
> Thanks,
> Jim, N7CXI
>
> k8mlm at aol.com  wrote:
>> Isao,
>>
>> The normal warm up time for  the Alpha 78 is 3 minutes.  However, dur to 
>> the age of the  caps and/or carbom comp resistors in the timer circuit 
the 
>> timer  may not work or take a long tome to turn on.
>>
>> I have an  old Alpha 77 and have to overhaul (replace caps anr 
resistors) 
>> on  the turn-on timer and active bias control boards to keep it 
operating  
>> properly.
>>
>> Bob
>>  K8MLM
>>
>>
>> -----Original  Message-----
>> From: isaonuma  <isaonuma at cablenet.ne.jp>
>> To:  amps at contesting.com
>> Sent: Tue, Dec 29, 2009 6:08 am
>>  Subject: [Amps] Alpha 78 Problem
>>
>>
>> Hello  all,
>>  I have recently bought Alpha 78 and it's faily clean. I  checked inside 
>> and
>> eemed OK. So I connected 220V line  and swithed on it. High voltage shows
>> 500V+ at CW, 2000V+ at SSB  mode. Air flow is OK and getting warmer 
little
>> y little. But, not  as mentioned in the manual there is no illumination 
of
>>  ale
>> ed or amber. I waited for 45-90 seconds, but there is any  change of 
light
>> or
>> ny click sound of relays. Maybe  there's some failure on 28VDC line. 
>> 'Cause
>>   didn't hear any sound from K2-Step start relay.
>> ny comments,  suggestions are appreciated.
>> 73, Isao JH1ROJ/KG8XV near Tokyo,  Japan
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