[Amps] Alpha 78 Problem

[Carl]

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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